You've probably heard it before, but I'll say it again:
The best single book on electronics (as practiced by folks
like us) is The Art of Electronics, by Paul Horowitz
and Winfield Hill. I've read a lot of books on electronics
and designed a lot of products, and this covers most
everything in enough detail to get you going.
The Art of Electronics
Horowitz & Hill
Cambridge University Press
ISBN 0-521-37095-7
This book begins with "What's a resistor", progresses through
capacitors and inductors, transistors, ICs, etc......and by
the end there's state machines, CPUs, micropower design, sensor
interfacing and the like. There's a bare minimum of heavy math,
replaced instead by good *intuitive* descriptions of what the
parts are doing. It even covers power-on-reset circuits! :-)
GO to the bookstore.
BUY the book.
SET it on the toilet tank.
READ a chapter on each visit.
You'll be an electronics guru in thirty days. Or maybe less,
depending on your diet. :-)
> GO to the bookstore.
> BUY the book.
> SET it on the toilet tank.
> READ a chapter on each visit.
>
> You'll be an electronics guru in thirty days. Or maybe less,
> depending on your diet. :-)
>Can anyone recommend a readily available power MOSFET with low on
>resistance (<0.03 ohm) when directly driven from a PIC output (5 volt
>supply). I ordered what looked like a promising device from Digi-key,
>only to find out that it was "vapor-ware". Current capacity required
>is modest, but must have low Ron. Thanks
>
>jk
If you can get +12V somewhere you can switch MOSFETS with the PIC. Just
connect the PIC output pin to the MOSFET gate and pull the gate to 12V with
a 10k or so resistor, larger means slower response when turning on. You
may want to put a small, 500 ohms or so, between the PIC and MOSFET gate.
This is to limit the short current spikes that may occur when discharging
the gate capacitance of the MOSFET. Now you can turn the MOSFET on my
making the PIC pin an INPUT, this should put the pin into a high impedance
state, letting the MOSFET gate be pulled high by the 10k resistor. To turn
the MOSFET off, just make the pin an output and drive it low, pulling the
MOSFET gate to ground.
>>Can anyone recommend a readily available power MOSFET with low on
>>resistance (<0.03 ohm) when directly driven from a PIC output (5 volt
>>supply). I ordered what looked like a promising device from Digi-key,
>>only to find out that it was "vapor-ware". Current capacity required
>>is modest, but must have low Ron. Thanks
>>
>>jk
>
>If you can get +12V somewhere you can switch MOSFETS with the PIC. Just
>connect the PIC output pin to the MOSFET gate and pull the gate to 12V
with a
>10k or so resistor, larger means slower response when turning on. You may
want
>to put a small, 500 ohms or so, between the PIC and MOSFET gate. This is
to
>limit the short current spikes that may occur when discharging the gate
>capacitance of the MOSFET. Now you can turn the MOSFET on my making the
PIC
>pin an INPUT, this should put the pin into a high impedance state, letting
the
>MOSFET gate be pulled high by the 10k resistor. To turn the MOSFET off,
just
>make the pin an output and drive it low, pulling the MOSFET gate to
ground.
>
>Hope this help,
>-shane
You might have a problem with this. Every i/o pin on a pic has protection
diodes
to both VSS and VDD. This limits the pin voltage to about 5.6 volts (if
vdd=5v).
I suppose you could get around this with yet another diode, but now it's
getting
a bit more complicated then the original request.
later .......
carl
Henry Carl Ott N2RVQ carlspam_OUTpipeline.com
------------------------------------------------
No wife, no horse, no spell checker.
------------------------------------------------
I've used a BUK553-100B logic level power mosfet manufactured by Philips
Semiconductors for switching from PICs - however its Rds(on) is about
0.22 ohms - higher than requested.
You could drive these via a 470R resistor from a PIC port pin. The resistor
should protect the PIC from any capactively coupled spikes on the gate
when switching large currents.
Unfortunately, as you want an Rds(on) < 0.03 ohms the Id capability tends
to be large and consequently the gate capacitance is also large. This means
the turn on will be very 'leisurely'.
The BUK106 might be useful as it is temperature & overload protected and
has an output pin to flag a fault condition.
Hope this is useful,
Sean Hagan
---------------------------------------
BIME
(Bath Institute of Medical Engineering) @spam@bimeKILLspambath.ac.uk
---------------------------------------
"John S. Kallend" <KILLspamMETMKALLENDKILLspamMINNA.ACC.IIT.EDU> wrote on
>Subject: power MOSFET that can be switched by PIC
>
>Can anyone recommend a readily available power MOSFET with low on
>resistance (<0.03 ohm) when directly driven from a PIC output (5 volt
>supply). I ordered what looked like a promising device from Digi-key,
>only to find out that it was "vapor-ware". Current capacity required
>is modest, but must have low Ron. Thanks
Hi John,
Harris makes N-Channel Logic Level Power FETs (MegaFETs). Their device
RFP50N05L has rDS(ON)= 0.027 Ohms at VGS=4V. Is that short enough for your
circuit?
Kind regards, Volkmar
---
Volkmar Gross, Softwork Telematica, Bremen, Germany (Fone&Phax: +49 421 74434)
>>>-----------------------------------------------------------------------------
>
Planck's quantum is the calorimetric equivalent of a Baud (Max Demon)
I recently bought some IRLZ44's from Digikey. They have an Rds of .028 ohms.
and are "logic level". They were in stock and arrived in three days. What
were you looking for?
--Chuck
>I am using a windowed PIC16C56 with a 32kHz oscillator. The power
>drawn when the window is open is a nice 15uA, but when I put a piece of
>black electrical tape over the window, the current consumption rises by
>a factor of 20. Does anyone have any idea why this is happening? All
>unused pins are grounded or pulled high.
Darwin:
Aaron had a good suggestion -- it's likely that you've failed to
initialize some registers, so your code isn't behaving properly when the
window's covered -- but the code he showed was for the 16C57. For your
16C56, use the following:
USEFSR EQU 0
FSR EQU 4
PORTA EQU 5
MOVLW PORTA ;PREPARE TO ZERO ALL REGISTERS EXCEPT
MOVWF FSR ;THE FSR, RTCC, PC, AND PROCESSOR STATUS
;REGISTERS.
CLRRAM CLRF USEFSR ;ZERO A REGISTER.
INCFSZ FSR ;HAVE WE DONE THEM ALL?
GOTO ZEROEM ;IF NOT, LOOP BACK AND ZERO ANOTHER.
>
> On Tue, 14 Mar 1995, Andy Hill wrote:
>
> > Darwin Hawes <TakeThisOuThawesEraseMEspam_OUTPHYSICS.UBC.CA> writes:
> > > On Fri, 10 Mar 1995, Andy Hill wrote:
> > > > If the problem is worse when the window is covered, I'd agree with
> > > > the "uninitialized register/port" crowd.
> > >
> > > That would have been my guess, except that the power consumption rises if
> > > I put on the cover on a running processor, so it is not an uninitialized
> > > port on power up. The processor seems to function both with and without
> > > the cover.
> > >
> > OK, and you stated earlier that the power consumption rises over a
> > period of seconds after you cover the processor window. Do you have
> > enough data to tell if the rise is linear or more of an exponential
> > (RC-time-constant) sort of progression? Do you have any tri-state
> > busses that aren't being driven for long periods of time? Any ports
> > that are in input-mode that aren't being driven or pulled-up?
>
> The rise seems to be non linear, but in the opposite sense as an RC time
> constant. It starts slowly, then increases rapidly, then stops. There
> were a few inputs that were not being driven, but changing these did not
> have any effect. I tried the same experiment with another 56, and a
> brand new '61. The other '56 worked better than the first, only rising
> to 0.1mA. The '61 had low power consumption with or without light. From
> this I would guess it was some sort of damage from the UV erasing that
> caused the problem.
>
>
What we have here is the photovoltaic effect. Small but with CMOS it doesn't
take much. The chip is acting like a solar cell and appling a small but
significant charge in the gate of a lot of the transistors. Not much, but
enough for them to leak a little bit each. Multiply by god knows how many
thousands and it becomes significant. The delay is due to the input capcitance
of the gate, it's real small, but then again the chip is silicon just not
optimized for the effect. The reason it doesn't build up enough to send
you off into the weeds is that you basicly have a no load solar cell that
has a max voltage just high enough to be noticeable, i.e. it barely gets
you into the linear region, but it can't switch the other half of the totem
pole.
Further some readings about several microcontroller lines, I've decided to use
the PIC serie of my applications. I just got my PICSTART16B development board
and hope to have my first hands-on experiences very soon (so you may say I'm a
novice). There're still few points I'd like to clarify; any help would greatly
be appreciated.
1) The 16C84 is an EEPROM device. Am I correct to assume that the program
memory can be erased? If so, how? With the PICSTART board?
2) Power consumption is minimal (~15uA) in the LP mode. Will it be about the
same in RC mode running at about 32kHz?
3) The options (clock mode, etc.) are selected with what is refered to as
<fuses>. On the erasable parts, are they burned permanently or are they
erased along with the program memory?
4) With the clock running in RC mode, substantial variations in frequency is
expected due to parts-to-parts variations (R, C, PIC itself, Vcc, etc.). For
given parts and conditions, what about the short term stability? For instance,
if the 60Hz is used as the primary clock, with the PIC keeping track of the
interval between cycles; is the RC clock stable enough to be used for backup
clock for let say few hours?
------------------------------------------------------------------------------
Marc Dion Defence Research Establishment Ottawa
Tel: (613) 998-2611 Fax: 990-9087 3701 Carling Ave, Ottawa, Ontario
Internet: RemoveMEmarc.dionTakeThisOuTdreo.dnd.ca Canada K1A 0Z4
Q1 Yes, Program memory can programmed/erased with the pickstart board for
erasable parts.
Q3. Yes, the fuses can be re-programmed with the programmer. Obviously if the
code protect fuse was blown then un-blowing it doesn't make the code
unproteced.
Q4. Don't know, but if time keeping is critical why not use a 32kHz watch
crystal as the low frequency might still keep power consumption low enough.
-Karl
--------------------------------------
Date: 3/21/95 6:03
To: Karl Grabe
From: pic microcontroller discussion
Further some readings about several microcontroller lines, I've decided to use
the PIC serie of my applications. I just got my PICSTART16B development board
and hope to have my first hands-on experiences very soon (so you may say I'm a
novice). There're still few points I'd like to clarify; any help would greatly
be appreciated.
1) The 16C84 is an EEPROM device. Am I correct to assume that the program
memory can be erased? If so, how? With the PICSTART board?
2) Power consumption is minimal (~15uA) in the LP mode. Will it be about the
same in RC mode running at about 32kHz?
3) The options (clock mode, etc.) are selected with what is refered to as
<fuses>. On the erasable parts, are they burned permanently or are they
erased along with the program memory?
4) With the clock running in RC mode, substantial variations in frequency is
expected due to parts-to-parts variations (R, C, PIC itself, Vcc, etc.). For
given parts and conditions, what about the short term stability? For
instance,
if the 60Hz is used as the primary clock, with the PIC keeping track of the
interval between cycles; is the RC clock stable enough to be used for backup
clock for let say few hours?
------------------------------------------------------------------------------
Marc Dion Defence Research Establishment Ottawa
On Jun 24, 11:07pm, "Kevin P. Fleming" wrote:
|Subject: Simple, cheap power supply
| Some time ago (maybe as much as 12 months) I saw an app. note and/or project
| desciption, probably in {Electronic Design} that used a Maxim part to create
| a small, low-current (50 ma or so) 5V DC power supply directly from the 120V
| AC line. There were very few other parts, possibly only a bridge rectifier.
|
| Does this ring any bells with anyone? Any points to an on-line presence for
| Maxim would be most welcome as well. Thanks in advance.
|-- End of excerpt from "Kevin P. Fleming"
Harris makes such a part. If you can't find any info, email me.
>On Jun 24, 11:07pm, "Kevin P. Fleming" wrote:
>|Subject: Simple, cheap power supply
>| Some time ago (maybe as much as 12 months) I saw an app. note and/or project
>| desciption, probably in {Electronic Design} that used a Maxim part to create
>| a small, low-current (50 ma or so) 5V DC power supply directly from the 120V
>| AC line. There were very few other parts, possibly only a bridge rectifier.
>|
>| Does this ring any bells with anyone? Any points to an on-line presence for
>| Maxim would be most welcome as well. Thanks in advance.
>|-- End of excerpt from "Kevin P. Fleming"
>
>Harris makes such a part. If you can't find any info, email me.
I think Linear Technology also makes a similar part. These circuits rectify
the 120V power then use a linear or sometimes switching regulator to reduce
it to 5 V. It is a nice demonstartion of IC fabrication capabilities to
make an IC that can handle 120 V. However, for the typical PIC project
where power consumption is only a few mA, usually the cheapest approach is
with discrete parts, and a conventional linear regulator.
It is very important to remember that with an offline supply like this, your
whole circuit will be at line potential. You can't count on any of the
wires in a "house current" circuit to be at a safe potential, other than the
ground wire of course, which isn't connected to any active parts of the
circuit. So all the inputs and outputs of the project will be "live,"
unless isolation devices are fitted. (If isolation devices are required, it
may be cheaper to use a conventional transformer-type power supply).
Switches and controls, if any, need to have apropriate safety approvals for
AC line potential use. The case must be designed so the customer has no
access to the conductors inside, even the "Vss" connected ones.
Customer-replaceable batteries can be a particular problem. In many
applications, these constraints are acceptable, for example if the circuit
is connected only to power-line devices, or if the input or output is by
radio (careful with external antennas) or IR light, etc. For safety, a
fuse, either a formal fuse or a fusible resistor, must be included in series
with the AC input. Fuses are not drawn in the diagrams below.
This is not the type of supply you want to use for piddling around with PICs
on the workbench. It is for production designs that are powered by AC to
begin with, meet the constraints of isolated I/O, and simpicity and cost
dominate.
During development and testing of such a device, a 1:1 ratio "Isolation
Transformer" must be used to prevent disasterous current flow from the
"return" side of the circuit thru line-powered meters, oscilloscopes,
engineers, programmers, and other test equipment, even then there will
always be parts of the circuit that are dangerous to touch.
With the safety issues understood, the simplest way to do it is:
(Probably the ASCII diagrams won't come out very well due to proportional
spacing)
AC HI -/\/\/--->|-------REG----- +5V
| | |
== | ==
| | |
AC LO--------------------|-------- VSS
This is a simple approach: the input of a conventional linear regulator is
fed with a half-wave rectified AC supply, with the current, and therefore
the rectified voltage, limited by a resistor. The resistor is chosen
experimentally to keep the input to the regulator in range, 8 to 35 V for a
78L05 type, over all possible line voltages. Typically it is in the range of
5K to 30K, and rated for several Watts. Of course, there must be a formula
for the resistor value, but I haven't derived it. If the power consumption
of the circuit varies a lot, then it may be necessary to fit a Zener diode
at the input of the regulator to keep the voltage there from soaring when
the 5V circuit isn't using much power. An obvious, often cheaper, variation
is to use only the Zener as a shunt regulator, eliminating the linear
regulator. It may be necessary to either- (1) increase the size of the
filter capacitor or (2) use a 2-stage filter before the zener - to reduce
ripple. The shunt regulator is probably best for really low-current
applications, where some ripple is tolerable.
Two-stage filter, mentioned in (2) above:
AC HI --/\/\/\---->|-----/\/\/\/------------- 5V
| | |
== == ~ (5.1 V Zener)
| | ^
| | |
AC LO------------------------------------VSS
For the 2-stage regulator, the second resistor is generally less resistance
(and less power) than the first one. Ripple voltage primarily appears on
the first capacitor, the low AC impedance of the second capacitor and the
Zener cause the second resistor to attenuate most of the ripple.
Efficiency (power dissipation in the resistors) is best if the DC voltage
on the first capacitor is kept low. Designing the 5V circuit to use a
relatively constant power makes the supply easier to do in any case.
The problem with resistive circuits is that a lot of power is wasted in the
resistor, requiring a fairly large resistor and provisions for keeping it
cool. An advanced (more expensive) technique is to use an inductor or
capacitor to absorb the excessive AC voltage in its reactance. Inductors
are generally not practical, but I mention them for completeness. The
capacitor circuit does have widespread application:
*?*
AC HI -/\/\/\--||---->|------REG------5V.
| | | |
~ == | ==
^ | | |
| | | |
AC LO--------------------------------- Vss
You may recognize the input to this circuit as a voltage doubler, indeed it
is, if a conventional diode were substituted for the Zener as the shunt
diode. However, by making the series capacitor small (approx 1 uF), the
output impedance of the doubled voltage is increased. The input capacitor
must be a bipolar film type, rated for at least the peak AC line voltage.
Electrolytic capacitors will not work here! The Zener acts as a shunt
regulator as well as a rectifier. The peak voltage on the first filter
capacitor is 0.7V lower than the Zener voltage due to the series diode, and
of course it may ripple below that as well. As with the dropping-resistor
version, the 3-terminal regulator may be replaced with a Zener shunt regulator.
The resistor marked *?* in the diagram above is so small (10-50 ohms) that
it is not a factor in normal operation. A 1/4 or 1/2 Watt unit will do, and
it shouldn't get hot. It's purpose is to attenuate spikes on the power line
that could couple through the capacitor and blow out the diodes. It is also
an opportunity to use a fusible resistor and kill two birds with one stone.
This circuit is used in a Radio Shack product (without the resistor, of
course), and I had the opportunity to get a returned unit from the bargain
bin, which had the Zener diode burned out. Radio Shack products are
sometimes a good buy at 10% of list price, but some re-engineering by the
customer may be required...
Again, caution is necessary when working with any circuit like these which
is directly connected to the power line!
Both ATT Microelectronics and Harris make chips that provide non-
isolated 5v power directly from the line. I think that Unitrode and Burr-
Brown may also. The Harris part number is 2405 -- but good luck trying
to get one! This seems like a part they prefer not to sell.
>Some time ago (maybe as much as 12 months) I saw an app. note and/or project
>desciption, probably in {Electronic Design} that used a Maxim part to create
>a small, low-current (50 ma or so) 5V DC power supply directly from the 120V
>AC line. There were very few other parts, possibly only a bridge rectifier.
>
>Does this ring any bells with anyone? Any points to an on-line presence for
>Maxim would be most welcome as well. Thanks in advance.
>
>
Harris HV-2405E World-Wide Single Chip Power Supply
- Data Sheet from October 1992 (14 pages)
App Note AN9217: High Current Off Line Power Supply
- App Note from January 1993 (11 pages)
It just happened that I ordered PCBs for the RS-232 Powered PIC16C84 programmer.
PCB can be assembled with either 78L05 or 5V6 Zener.
Anybody interested?
Both plain PCBs as fully mounted and tested kits will be available next week.
Plain PCB: 6 USD (including postage to any location world wide).
Full kits will also be available at close to manufacturing cost prices.
Qty discounts start at qty 2!
Complete ordering info will be on our WWW pages within few days.
antti
----------------------------------------------------------
-- Antti Lukats Silicon Studio --
-- EraseMEsisrasi.lr.ttu.ee PO Box 3500 --
-- ftp://rasi.lr.ttu.ee/pub/sis Tallinn EE0001 --
-- http://rasi.lr.ttu.ee/~sis Estonia --
----------------------------------------------------------
Does anyone have any hints or tips on powering a PIC from a phone
line (yes I know, one would have to get type aproval to sell them).
Does one just use the same sort of diode chain clamp that is found in
IC telephone circuits.
I seem to recall someone asked about a similar problem but am not sure
if it was to do with phone lines.
Some of the applications I have in mind are dialtone checker, ring-counter
and perhaps even a call metering device. Power is available in
large quantities when off hook (10 V at 50-60mA) but for the ring
counter I would like to load the line as little as possible, Is there
a 10-48V to 5V switching converter IC from maxim or the like that is
used.
Cheers Kalle
--
Kalle Pihlajasaari RemoveMEkalleEraseMEEraseMEdata.co.za
Interface Products Box 15775, Doornfontein, 2028, South Africa
+27 (11) 402-7750 Fax: +27 (11) 402-7751
>Hi,
>
>Does anyone have any hints or tips on powering a PIC from a phone
>line (yes I know, one would have to get type aproval to sell them).
>
>Does one just use the same sort of diode chain clamp that is found in
>IC telephone circuits.
>
>I seem to recall someone asked about a similar problem but am not sure
>if it was to do with phone lines.
>
>Some of the applications I have in mind are dialtone checker, ring-counter
>and perhaps even a call metering device. Power is available in
>large quantities when off hook (10 V at 50-60mA) but for the ring
>counter I would like to load the line as little as possible, Is there
>a 10-48V to 5V switching converter IC from maxim or the like that is
>used.
If such a project will eventually be offered for sale, the first step would
be to research the FCC or other regulations to see how much power you're
allowed to draw from the phone lines. Most phones seem to use a 10 M
resistor to keep the RAM alive while on-hook, that is only 4.8 uA, but a PIC
in standby mode could survive on that. I don't think the switching
converter would justify its complexity, and is likely to couple switching
noise out to the phone line that could cause trouble with certification. If
you need more than a few uA continously while in standby a battery is
probably going to be required.
Plan on SLEEPing the PIC a lot, and supplying brief bursts of power to it
from a large capacitor when it is actually running. It may also be feasible
to use a really slow RC oscillator, which is speeded up by switching in a
smaller resistor from a port pin when more computing power is required. A
simple Zener shunt should do, unless the device is to take over the line
completely. The "line in use" detector could include a bypass of the
resistor to boost available current while the line is in use. When the
phone rings, it is also permissible to draw a relatively large amount of
power. This can be accomodated by AC-coupling the line to another rectifier.
Phone lines can be an excellent source of surges, so sending the raw line
inputs through small value resistors then a shunt MOV is a real good idea to
protect the circuit.
I am just starting to use pic devices. I have just designed a PCB using a
PIC16c55 as a logic controller for a system controling three phase contacors.
The PCB opperates correctly on the bench, but once connected in it's real
situation, it starts to reset almost every time one of the coils for the
contactors comes in.
I am not sure, but I think my problem may lie in the way I have connected
the periferal components to the PIC. For example I am not sure of values
for a reliable power on reset circuit. It is hard for me to know exactly
what is causing my PCB to reset, but an interesting point I noted was
that a 'Power-On' LED connected directly to the 5v suppy flickers sometimes
when the coils in the system power down, but if I remove the PIC from the
board it no longer flickers with the coils. It's almost as if the PIC is
somehow having an extream loading effect on the power supply (but only when
there are voltage transients around).
Could anyone give me any tips as to the configuration of a reliable set of
components external to the PIC.
Or, could anyone point me in the direction of information (diagrams) to
let me know what a good setup is.
>I am just starting to use pic devices. I have just designed a PCB using a
>PIC16c55 as a logic controller for a system controling three phase contacors.
>The PCB opperates correctly on the bench, but once connected in it's real
>situation, it starts to reset almost every time one of the coils for the
>contactors comes in.
>
>I am not sure, but I think my problem may lie in the way I have connected
>the periferal components to the PIC. For example I am not sure of values
>for a reliable power on reset circuit. It is hard for me to know exactly
>what is causing my PCB to reset, but an interesting point I noted was
>that a 'Power-On' LED connected directly to the 5v suppy flickers sometimes
>when the coils in the system power down, but if I remove the PIC from the
>board it no longer flickers with the coils. It's almost as if the PIC is
>somehow having an extream loading effect on the power supply (but only when
>there are voltage transients around).
>
>Could anyone give me any tips as to the configuration of a reliable set of
>components external to the PIC.
>
>Or, could anyone point me in the direction of information (diagrams) to
>let me know what a good setup is.
>
>Any assistance would be greatly appreciated,
>
>Thanks,
>
>Wayne G Boyd.
Sounds like inductive kickback from the coils. Have this problem at work
all the time. Common solutions are to put a diode across the coil, and add
an RC circuit. I've also had luck using an opto-isolator or
solid-state-relay between the offending device and digital controller. (Had
a lot of problems once with a solenoid resetting a 8255 everytime it turned
off. The software "engineer" wanted to "solve" the problem by just
re-configuring the 8255 each time the solenoid turned off)
Chris
----------------------------------------------------------------------------
|Check out my WWW page at http://www.access.digex.net/~cps/ for scientific |
|software for the Mac, Free Radio, Shortwave Radio, and Spy Numbers Stations |
|information. |
|Finger me (RemoveMEcpsspam_OUTKILLspamaccess.digex.net) for my PGP Public Key |
----------------------------------------------------------------------------
"Those who would sacrifice liberty for security deserve neither."
-Ben Franklin
Depending on the type and size of contactors being using, not only do
they generate a large inrush of current (most spec inrush current
as well as holding current), they can generate large amounts of EMI.
I found that I had to remove the controller assembly from the motor
starter cabinet to completly solve the problem (prior to redesigning it
to use a PIC). I have yet to put it back in the same box, as it works
out cheaper to use seperate cabinets. These are 460 VAC 3 phase motor
controls.
I have a few questions concerning power on reset of a PIC (specifically
the PIC16c54/56). My chip is RC osc configured to run really slow
(probably 5hz)
If I have the watchdog timer set, is it active if the chip doesn't power
up reset properly?
Right now I do not have the watchdog timer set up, but
when the power droops and then comes back up, the PIC is hung. Will a
WDT help in this case? Would an off chip power on reset circuitry
prevent this? I am not looking to maintain the current program, I just
want to reliably reset the PIC.
I don't have oscilloscope measurements yet to see how low the line
droops. The droop is just caused by myself trying to torture test my
final circuit (remove power and reapply before the filter cap
discharges).
Is part of the reason for this my very slow clock speed?
>I have a few questions concerning power on reset of a PIC (specifically
>the PIC16c54/56). My chip is RC osc configured to run really slow
>(probably 5hz)
>
>If I have the watchdog timer set, is it active if the chip doesn't power
>up reset properly?
>
>Right now I do not have the watchdog timer set up, but
>when the power droops and then comes back up, the PIC is hung. Will a
>WDT help in this case? Would an off chip power on reset circuitry
>prevent this? I am not looking to maintain the current program, I just
>want to reliably reset the PIC.
>
> I don't have oscilloscope measurements yet to see how low the line
>droops. The droop is just caused by myself trying to torture test my
>final circuit (remove power and reapply before the filter cap
>discharges).
The built in power-on reset circuit is not guaranteed to work unless Vdd
starts at 0V and rises at least 0.05 V/ms. So it will not always reset
after a "brownout". Using the WDT should help, it's always a good idea in
any application unless extremely low power is required. However, even with
the prescaler engaged at a rate of 128, the WDT may cause a reset every (9ms
* 128) = 1150 ms = 0.86 Hz. Since your X1 clock is only 5 Hz, the
instruction rate is 1.25 Hz, less than twice the rate than the WDT expires.
So there'd be no way to execute enough CLRWDT instructions to stave off a
reset if the WDT in your chip was the worst case of 9 ms. (well you could,
but every instruction in the program would have to be CLRWDT, not any time
to do anything else.)
Best bet would be to use an external voltage detector such as the MN13811
ones sold by Digi-Key to pull the reset pin low when the voltage drops. The
Microchip data book shows a few voltage detectors that can be built with
discrete components but an integrated one is probably < $0.50 in quantity
and requires only one TO-92 unit and a pull-up resistor.
----------
>>I have a few questions concerning power on reset of a PIC (specifically
>>the PIC16c54/56). My chip is RC osc configured to run really slow
>>(probably 5hz)
>>
>>If I have the watchdog timer set, is it active if the chip doesn't power
>>up reset properly?
>>
================ reply ---------
I found that on a 16C71, the 'external power on reset circuit'
16C5X fig 13.1.1 was needed to keep it from hanging up.
---------
Bill Cornutt EraseMEbillcornspamspamBeGoneinfoserv.com
Located in Ione California USA.
A small town in Northern California.
Sitting against the foothills of the Mother Lode.
----------------------------------------------------
Anyone know the current consumption of a `c71 during A/D conversion at
3.3v using the internal RC osc? I'm building a battery monitor/charger
where current drain is critical.
I am making a project that uses a PIC to control a high power ultrasonic
wave. I want to take a gas (very small amount) and comxress it in a closed
space with an ultrasonic wave (like a tiny air compressor). The only problem
is I am having a hard time finding information on building a high power
ultrasonic wave generator. I looked at some small ultrasonic transducers but
they don't seem to be strong enough to do anything. If anyone has any ideas
I would be very interested to here them. Thanks in advance.
Hi PICers,
I blew up the power supply of my PICStart board. The truth
is i didn't do anything weird. I connected it to my PICstart board
and a few minutes later it blew up with a loud 'BAAAMMM". I should point
out that this happened after i opened my brand new PICStart board.
I looks like a "bell curve" fault. The board works OK.
The problem is the following:
I wanna repair the power supply (Microchip distributor here didn't
have spare items) because it's so damn beautiful. Very delicate
constuction. The thing that blew up seems to be a resistor.
A part of it is missing :-) What puzzles me is the connection of that
resistor.
MAINS
O------+--fuse--+--resistor-+---+one end of the transformer coil
PLUG |
O------+------------------------+other end of the transf. coil
Is this supposed to be like that? What the heck the resistor does there?
Consumes energy for nothing?
The resistor must be a 10 Ohm one (brown, black, black).
I would like to hear from you on this as well as any other ideas you may
have on what all these ICs, coils and stuff are doing there. (Don't tell
me they do voltage regulation, 'cause i'm not buing it :-) )
>Hi PICers,
>I blew up the power supply of my PICStart board. The truth
>is i didn't do anything weird. I connected it to my PICstart board
>and a few minutes later it blew up with a loud 'BAAAMMM". I should point
>out that this happened after i opened my brand new PICStart board.
>I looks like a "bell curve" fault. The board works OK.
>The problem is the following:
>I wanna repair the power supply (Microchip distributor here didn't
>have spare items) because it's so damn beautiful. Very delicate
>constuction. The thing that blew up seems to be a resistor.
>A part of it is missing :-) What puzzles me is the connection of that
>resistor.
> MAINS
>O------+--fuse--+--resistor-+---+one end of the transformer coil
> PLUG |
>O------+------------------------+other end of the transf. coil
>
>Is this supposed to be like that? What the heck the resistor does there?
>Consumes energy for nothing?
>The resistor must be a 10 Ohm one (brown, black, black).
>
>I would like to hear from you on this as well as any other ideas you may
>have on what all these ICs, coils and stuff are doing there. (Don't tell
>me they do voltage regulation, 'cause i'm not buing it :-) )
>
>
>Spiros Papageorgiou
>
I'm sorry for your incident. With that resistor link directly to the main
supply through fuse, the current passing through that resistor is almost
220v/10=22 A. That's too much already. No wonder that resistor blown up.
You should contact your dealer about it. You are right, that resistor
shouldn't be there. Must be construction error. Try bypass that resistor by
linking the fuse directly to the input of the transformer.
>At 06:36 PM 10/17/95 +0200, you wrote:
>>Hi PICers,
>>I blew up the power supply of my PICStart board. The truth
>>is i didn't do anything weird. I connected it to my PICstart board
>>and a few minutes later it blew up with a loud 'BAAAMMM". I should point
>>out that this happened after i opened my brand new PICStart board.
>>I looks like a "bell curve" fault. The board works OK.
>>The problem is the following:
>>I wanna repair the power supply (Microchip distributor here didn't
>>have spare items) because it's so damn beautiful. Very delicate
>>constuction. The thing that blew up seems to be a resistor.
>>A part of it is missing :-) What puzzles me is the connection of that
>>resistor.
>> MAINS
>>O------+--fuse--+--resistor-+---+one end of the transformer coil
>> PLUG |
>>O------+------------------------+other end of the transf. coil
>>
>>Is this supposed to be like that? What the heck the resistor does there?
>>Consumes energy for nothing?
>>The resistor must be a 10 Ohm one (brown, black, black).
>>
>>I would like to hear from you on this as well as any other ideas you may
>>have on what all these ICs, coils and stuff are doing there. (Don't tell
>>me they do voltage regulation, 'cause i'm not buing it :-) )
>>
>>
>>Spiros Papageorgiou
>>
>I'm sorry for your incident. With that resistor link directly to the main
>supply through fuse, the current passing through that resistor is almost
>220v/10=22 A. That's too much already. No wonder that resistor blown up.
>You should contact your dealer about it. You are right, that resistor
>shouldn't be there. Must be construction error. Try bypass that resistor by
>linking the fuse directly to the input of the transformer.
Just picking up the mail after a few days off. So I hope you have not tried
to make the power supply work without the resistor. Because then it will
really blow!
The resistor is there to provide current limiting. The 220/10 current only
applies for less than a 1/10 of a second. After that the impedance of the
tranformer becomes quite significant. The resistor is there to limit the
inrush overvoltage spike on the transformer output that otherwise would be
created. That it blew up tells you that the transformer was drawing too much
current. Two possible reasons for that: Shorted output, or shorted primary
winding. Since it's brand new and you did not say you had it plugged in, the
fault is most likely a 'turn to turn' short in the winding (thats a
manufacturing defect). Very hard to fix, because you have to take the core
appart to unravel the winding, and the wire will likely get damaged as you
unravel it.
Hope I didn't overdo it, but this is the first thing I've read that I really
understand something about. See, I'm just learning about PIC's.
Hugo
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Hugo Ahrens, IAI Industrial Automation Inc.
e-mail --> spamBeGonehahrensSTOPspamEraseMEdirect.ca
fax --> 604-576-9516
phone --> 604-576-6717
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I've just started using PIC devices (in fact, I'm almost entirely green
at any sort of electronics). Having done "flashing LED" and "buzzing
speaker", I'm ready to build something a little more useful, a digital
metronome.
Does anybody know how to produce a reasonably loud "click" from a
3V battery powered circuit? I tried sending a square pulse to a
teensy weensy miniature speaker, but it's very quiet.
Programmer Software for Free
============================
I built the 16C84 in-circuit programmer
from the application note AN589 -- it worked perfectly first time. I
have built a rudimentary software user interface for the PC in Turbo C
(using Analog Design Specialists low level code). With this I can
download .hex files from MPASM directly into the device. The code
only overwrites locations which require changing, to reduce eeprom
cycles during development.
I'd be happy to release my source code (although it still has some
very rough edges!) if there is demand.
Cheers
Andrew Kay
Sharp Labs Europe Ltd, Oxford Science Park, Oxford UK, OX4 4GA KILLspamAndrew.KayspamBeGonesharp.co.uk Tel:+44 1865 747711 FAX:+44 1865 747717
I've just started using PIC devices (in fact, I'm almost entirely green
at any sort of electronics). Having done "flashing LED" and "buzzing
speaker", I'm ready to build something a little more useful, a digital
metronome.
Does anybody know how to produce a reasonably loud "click" from a
3V battery powered circuit? I tried sending a square pulse to a
teensy weensy miniature speaker, but it's very quiet.
Programmer Software for Free
============================
I built the 16C84 in-circuit programmer
from the application note AN589 -- it worked perfectly first time. I
have built a rudimentary software user interface for the PC in Turbo C
(using Analog Design Specialists low level code). With this I can
download .hex files from MPASM directly into the device. The code
only overwrites locations which require changing, to reduce eeprom
cycles during development.
I'd be happy to release my source code (although it still has some
very rough edges!) if there is demand.
Cheers
Andrew Kay
Sharp Labs Europe Ltd, Oxford Science Park, Oxford UK, OX4 4GA EraseMEAndrew.KayEraseMEsharp.co.uk Tel:+44 1865 747711 FAX:+44 1865 747717
> Does anybody know how to produce a reasonably loud "click" from a
> 3V battery powered circuit? I tried sending a square pulse to a
> teensy weensy miniature speaker, but it's very quiet.
The emitter follower pair can drive the low-impedance speaker much
better than the PIC port pin. The decoupling capacitor makes sure the speaker
sees an AC signal. IF this is not enough noise, duplicate the emitter
follower, and connect to the other side of the speaker, then drive from
another port pin in anti-phase with the first pin. This will swing twice
the supply voltage across the speaker, peak-to-peak. That should get you about
6dB more noise. If you do that, the capacitor may not be required (but I'd
probably leave it there. Be sure to set both port pins high or low when no
noise is required, to avoid reverse polarizing the capacitor, in this case.)
Also, to maximise the noise from the speaker, try baffling it, or even clamping
it directly onto a hard surface - at some frequencies a small speaker will
radiate better from the back of the speaker than the front. Just sitting in
free air is bad. Also, the larger the speaker the better - small speakers
are inefficient.
On low voltages, the base-emitter voltage drop of the emitter follower is
significant
so you might want to use some other circuit where the load is in the collector
side, but driving the transistors is harder - you can't just connect the bases
together
as in this circuit.
I've tested the above circuit on 5V, and it makes an impressive sound from a 1"
speaker at about 1000Hz - a double-ended version on 3V should be slightly
better.
Happy metrognoming. Where do the best gnomes go to school? The London
School of Eco-gnomics!
--
Clyde Smith-Stubbs | HI-TECH Software, | Voice: +61 7 3300 5011 @spam@clyde@spam@spam_OUThitech.com.au | P.O. Box 103, Alderley, | Fax: +61 7 3300 5246 http://www.hitech.com.au | QLD, 4051, AUSTRALIA. | BBS: +61 7 3300 5235
----------------------------------------------------------------------------
FREE! Download our shareware (FREE for noncommercial use) MS-DOS C Compiler!
Point your Web browser at http://www.hitech.com.au/
> Does anybody know how to produce a reasonably loud "click" from a
> 3V battery powered circuit? I tried sending a square pulse to a
> teensy weensy miniature speaker, but it's very quiet.
The emitter follower pair can drive the low-impedance speaker much
better than the PIC port pin. The decoupling capacitor makes sure the speaker
sees an AC signal. IF this is not enough noise, duplicate the emitter
follower, and connect to the other side of the speaker, then drive from
another port pin in anti-phase with the first pin. This will swing twice
the supply voltage across the speaker, peak-to-peak. That should get you about
6dB more noise. If you do that, the capacitor may not be required (but I'd
probably leave it there. Be sure to set both port pins high or low when no
noise is required, to avoid reverse polarizing the capacitor, in this case.)
Also, to maximise the noise from the speaker, try baffling it, or even clamping
it directly onto a hard surface - at some frequencies a small speaker will
radiate better from the back of the speaker than the front. Just sitting in
free air is bad. Also, the larger the speaker the better - small speakers
are inefficient.
On low voltages, the base-emitter voltage drop of the emitter follower is
significant
so you might want to use some other circuit where the load is in the collector
side, but driving the transistors is harder - you can't just connect the bases
together
as in this circuit.
I've tested the above circuit on 5V, and it makes an impressive sound from a 1"
speaker at about 1000Hz - a double-ended version on 3V should be slightly
better.
Happy metrognoming. Where do the best gnomes go to school? The London
School of Eco-gnomics!
--
Clyde Smith-Stubbs | HI-TECH Software, | Voice: +61 7 3300 5011 spamBeGoneclydeKILLspamhitech.com.au | P.O. Box 103, Alderley, | Fax: +61 7 3300 5246 http://www.hitech.com.au | QLD, 4051, AUSTRALIA. | BBS: +61 7 3300 5235
----------------------------------------------------------------------------
FREE! Download our shareware (FREE for noncommercial use) MS-DOS C Compiler!
Point your Web browser at http://www.hitech.com.au/
At 09:46 AM 20/12/95 GMT, you wrote:
>I've just started using PIC devices (in fact, I'm almost entirely green
>at any sort of electronics). Having done "flashing LED" and "buzzing
>speaker", I'm ready to build something a little more useful, a digital
>metronome.
>
>Does anybody know how to produce a reasonably loud "click" from a
>3V battery powered circuit? I tried sending a square pulse to a
>teensy weensy miniature speaker, but it's very quiet.
>
Instead of a click, try getting a very short beep - just a few cycles worth.
If the 3V is not enough you could use an H bridge to drive it. Two LM 386s
or something similar should do it.
Prashant
+----------------+ -------------------------------------------------
| | Prashant Bhandary
| +---+ | Spatial Information Systems Section
| | | | Roads and Traffic Authority
| | | | Rosebery NSW 2018, AUSTRALIA
| | | | Tel: +61-2-662 5299
| | +----+ | Fax: +61-2-662 5348
| | | | Email: .....prashbspam_OUTrta.oz.au
| +--------+ |
| Still a newbie | "2b|!2b" - William Shakespeare
+----------------+ -------------------------------------------------
> >Does anybody know how to produce a reasonably loud "click" from a
> >3V battery powered circuit? I tried sending a square pulse to a
> >teensy weensy miniature speaker, but it's very quiet.
> >
>
> Instead of a click, try getting a very short beep - just a few cycles worth.
> If the 3V is not enough you could use an H bridge to drive it. Two LM 386s
> or something similar should do it.
Actually, I'd suggest sending it a short burst of "random" pulses. Metronomes
that beep with a definite pitch can be a bother musically if their output is
off-key. If you use random pulses, the resulting sound would be white or pink
noise, and thus less likely to be bothersome.
Also, for output you could tie one leg of the speaker to a port pin, and
the other to a port pin via a cap. If both port pins switch simultaneously
in opposite directions you could get +/- 6 volts on the speaker which should
give it a louder drive than merely using a single port pin.
> Programmer Software for Free
> ============================
> I built the 16C84 in-circuit programmer
> from the application note AN589 -- it worked perfectly first time. I
> have built a rudimentary software user interface for the PC in Turbo C
> (using Analog Design Specialists low level code). With this I can
> download .hex files from MPASM directly into the device. The code
> only overwrites locations which require changing, to reduce eeprom
> cycles during development.
>
> I'd be happy to release my source code (although it still has some
> very rough edges!) if there is demand.
I homebrewed two PIC program softwares myself [one in TC, one in QuickBasic
when I accidentally left the TC one at home]. What do you use for printer
port pins? I used to use 1=Strobe=D7, 2=Data0=Clock 3=Data1=/MCLR 4=+VPP
[high turns it on] but unfortunately on Toshiba laptops pin 1 is not open-
collector, and pin 14 [my second choice] is open-collector but its readback
register shows the latched value rather than its physical state. Thus, I
strap 14 and 15, both of which go to D7 on the PIC; 14 is the output, 15 the
readback. How do you work things?
> Also, for output you could tie one leg of the speaker to a port pin, and
> the other to a port pin via a cap. If both port pins switch simultaneously
The trouble with this is that the output impedance of the port pins is
too high to effectively drive a low-impedance speaker. Either use an
amplifier, an emitter-follower setup like I previously described, or
a higher-impedance speaker. Telephone earpieces work quite well. They
produce a surprising amount of noise.
The random noise approach is good, but if you're outputting a click
consisting of a few cycles, then the actual pitch of the tone is
not going to make much difference, and if there is too much variance
between clicks that would not be good.
--
Clyde Smith-Stubbs | HI-TECH Software, | Voice: +61 7 3300 5011 TakeThisOuTclyde.....TakeThisOuThitech.com.au | P.O. Box 103, Alderley, | Fax: +61 7 3300 5246 http://www.hitech.com.au | QLD, 4051, AUSTRALIA. | BBS: +61 7 3300 5235
----------------------------------------------------------------------------
FREE! Download our shareware (FREE for noncommercial use) MS-DOS C Compiler!
Point your Web browser at http://www.hitech.com.au/
Andew asked:
> > >Does anybody know how to produce a reasonably loud "click" from a
> > >3V battery powered circuit? I tried sending a square pulse to a
> > >teensy weensy miniature speaker, but it's very quiet.
Someone answered:
> > Instead of a click, try getting a very short beep - just a few cycles worth.
> > If the 3V is not enough you could use an H bridge to drive it. Two LM 386s
> > or something similar should do it.
John replied:
> Actually, I'd suggest sending it a short burst of "random" pulses.
good idea!
>
> Also, for output you could tie one leg of the speaker to a port pin, and
> the other to a port pin via a cap. If both port pins switch simultaneously
> in opposite directions you could get +/- 6 volts on the speaker which should
> give it a louder drive than merely using a single port pin.
But why do I have to tie one leg of the speaker to a PIC pin _via a cap_?
It _is_ the advantage of a bridge speaker driver not to need any cap!
For example, have a look at the data sheet of a TDA7052 audio amplifier
(from Philips). The data sheet proudly claims that no external components
are needed (well, except for 1 resistor and 1 big cap for Vdd).
I think this IC could be used as a single-chip solution for the speaker-driver
problem, although it might not be the cheapest way.
> > Also, for output you could tie one leg of the speaker to a port pin, and
> > the other to a port pin via a cap. If both port pins switch simultaneously
> > in opposite directions you could get +/- 6 volts on the speaker which should
> > give it a louder drive than merely using a single port pin.
> But why do I have to tie one leg of the speaker to a PIC pin _via a cap_?
> It _is_ the advantage of a bridge speaker driver not to need any cap!
True it's nice to avoid a cap, but you'll almost certainly need either a cap
or a resistor to limit current, and if you use a cap it will allow a higher
peak current initially, and store current fed to it during one cycle for out-
put in the next. Thus, assuming an initial steady state with the cap's port
pin high and the other one low, we have [all voltages relative to ground]:
PIN CAP CAP [SPKR] PIN
3.0 3.0 0.0 0.0
If we switch the high/low on the port pins we then have
0.0 0.0 -3.0 3.0
[six volts one polarity on the speaker--twice Vdd]
After a little while, the cap will equilibrate to
0.0 0.0 3.0 3.0
which after another click becomes
3.0 0.0 6.0 0.0
[six volts other polarity on the speaker--twice Vdd]
So the effect of the cap is to double your peak voltage, though at the
expense of horrendously distorting your frequency response (not an issue
for a metronome producing "clicks")
>Does anybody know how to produce a reasonably loud "click" from a
>3V battery powered circuit? I tried sending a square pulse to a
>teensy weensy miniature speaker, but it's very quiet.
>
Try using a piezo speaker, and hitting it with a train of pulses, say 10
milli-seconds of a 4 KHz (250 uS period) square wave. If its too short to
sound like a tone, it will sound like a click. Drive the speaker with two
port lines (complemented, 180 phase) with an appropriate inductor in
parallel with the piezo, around 100mH, to get a louder signal, or use an
audio step-up transformer. Common piezo's are around .001uF.
>Programmer Software for Free
>============================
...
>I'd be happy to release my source code (although it still has some
>very rough edges!) if there is demand.
Hi all,
In some e-mails about home automation I saw something about hybrid modules
for transmitting data on power line.would you please say me more information
about them and where can i buy them?I need them very much and thanks for all
replies before.
Ashkan Marami
E-mail: TakeThisOuTMaramiKILLspamspamrose.ipm.ac.ir
Such a device is the TW523 X10 transceiver which is available from companies
that sell X10 devices. This unit looks like a wall charger with a LED on it
that is normally on all the time and flickers when X10 signals are
received.
The TW523 connects to the world via a RJ11 telephone modular-style cable,
but you want to be darn sure that whatever cable you use is a straight-through
cable or you at least know how it is configured as many telephone cables
have a twist so to speak in them which reverses the polarity of the two pairs
at the other end.
All the connections on the TW523 are opto-isolated. There is a common
pin, a 60 or 50HZ square-wave open-collector signal for zero-crossing
detection, data in, and data out.
The TW523 has a tiny bit of intelligence in that it will only
relay valid X10 signals to the data-out pin. I am told that this has the
side-effect of eating every other "Dim" packet when somebody uses a X10
controller to dim a light.
If you want to transmit X10 signals, you must format and time them
properly before sending them to the TW523 Data-in pin. I seem to recall that
you are sending to the LED of an opto isolator so you must provide proper
current limiting on the output device you are using.
There are even versions of this device designed for the 230-volt 50HZ power
systems.
I hope this helps.
Martin McCormick WB5AGZ Stillwater, OK 36.7N97.4W
OSU Center for Computing and Information Services Data Communications Group
In message <.....m0tTU8V-0000nZCRemoveMEdc.cis.okstate.edu>, Ali Marami writes:
>Hi all,
>In some e-mails about home automation I saw something about hybrid modules
>for transmitting data on power line.would you please say me more information
>about them and where can i buy them?I need them very much and thanks for all
>replies before.
>Ashkan Marami
>E-mail: RemoveMEMaramispamBeGonerose.ipm.ac.ir
Here's a brain buster.
We have a stand alone CO gas monitor (safety equipment) that uses a
PIC16C74.
If the power supply is momentarily shorted (milliseconds), the PIC does
not recover, but locks up in random modes.
We have the Watchdog timer ON and CLRWDT is only given one time in the
main program loop.
Any ideas? I was massacred today in an engineering meeting as this
instrument was on the verge of its first major shipment.
Thanks.
--
Regards, James Musselman, President
Radix/Cobalt Instruments, Inc.
PO Box 897
Clovis, CA 93613 USA
tel 209-297-9000
fax 209-297-9400
On Apr 3, 11:02am, James Musselman wrote: {Quote hidden}
> Subject: Power Brown Outs
> Here's a brain buster.
> We have a stand alone CO gas monitor (safety equipment) that uses a
> PIC16C74.
> If the power supply is momentarily shorted (milliseconds), the PIC does
> not recover, but locks up in random modes.
> We have the Watchdog timer ON and CLRWDT is only given one time in the
> main program loop.
> Any ideas? I was massacred today in an engineering meeting as this
> instrument was on the verge of its first major shipment.
> Thanks.
>
> --
> Regards, James Musselman, President
>
> Radix/Cobalt Instruments, Inc.
> PO Box 897
> Clovis, CA 93613 USA
> tel 209-297-9000
> fax 209-297-9400
>
> Check out my home page http://rdx.com
>-- End of excerpt from James Musselman
Sounds like a tough day at the office!
You could try enough bulk capacitance on your board to ride through the short.
Or add circuitry to hold the PIC in reset until the supply voltage recovers.
Motorola makes a part for micro-processor resets.
Regards,
Brad Morrow
--
-
--------------------------------------------------------------------------
Brad Morrow Advanced Systems Division
Product Design e-mail: spamBeGonemorrow@spam@spam_OUTasd.sgi.com
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2011 N. Shoreline Blvd. fax: (415)961-9075
Mountain View, CA 94039-7311
--------------------------------------------------------------------------
I had the same problem, but fortunately my product was in the
early prototype stage at the time. The PIC's main CPU and
oscillator sections start up at a lower voltage than does the
memory, thus locking the chip up upon brown-out or power-up
when the supply doesn't ramp up quick enough.
The watchdog timer will only protect you against software
lock-up, not against the CPU core itself going off into the
twilight zone, which is what it sounds like you have here.
Without getting into too much detail on the various power-up
requirement specs, the internal power-up timer (PWRT) and
oscillator start-up timer (OST) specs, you can simply enable
the PWRT if your power supply will always ramp up in less than
28ms AND the supply shuts off at low voltage instead of going
into un-regulation mode.
If your power supply can't do that, then simply toss a Motorola
MC34064 onto the /MCLR (active low RESET) pin, along with a cap
and resistor or two if you like. This is a little 3 pin
undervoltage sensing IC, and will hold the '74 in reset unless
the voltage is above 4.6 V. It comes in many different
flavours like wider temperature ranges, different cutoff
voltage like 4.3 or 2.7 volts, TO-92 or SO-8 packages, etc.
Similiar devices are available from many other manufacturers.
Oh, and they cost way less than $1 U.S. each in low quantities.
The microchip databook shows some other cheap alternative
brown-out protection circuits.
Of course, Microchip has realized this deficiency in the
standard '74 as well, and have introduced the '74A as a result.
As far as I can tell (note the subtle disclaimer) the only
difference is the addition of a brown-out reset circuit (BOR).
When enabled via the BODEN bit (love those acronyms) the BOR
will hold the device in reset once VDD falls below about 4V,
and will keep it in reset until VDD has remained above 4V for
more than 28 to 132ms (72ms nominal).
For the BOR to kick in and reset the chip, VDD must remain
below 4V for at least 100usec. I assume that Microchip in
their wisdom has made this delay less than the time is takes
the chip lock up, though I could find no indication or
guarantee of this in the databook.
So basically you have three choices: Improve your power
supply, add in something like a MC34064 (happy rework & PCB
changes), or go for the 74A's and save your '74 stock for a
future project. Now get in there and call another meeting to
say you've got a fix. Ok, maybe test it first.
-Ed VanderPloeg.
______________________________ Reply Separator _________________________________
Subject: Power Brown Outs
Author: pic microcontroller discussion list <TakeThisOuTPICLISTspamMITVMA.MIT.EDU> at
InterNet
Date: 4/3/96 7:34 PM
Here's a brain buster.
We have a stand alone CO gas monitor (safety equipment) that uses a
PIC16C74.
If the power supply is momentarily shorted (milliseconds), the PIC does
not recover, but locks up in random modes.
We have the Watchdog timer ON and CLRWDT is only given one time in the
main program loop.
Any ideas? I was massacred today in an engineering meeting as this
instrument was on the verge of its first major shipment.
Thanks.
--
Regards, James Musselman, President
Radix/Cobalt Instruments, Inc.
PO Box 897
Clovis, CA 93613 USA
tel 209-297-9000
fax 209-297-9400
A possible answer to:
>Here's a brain buster.
>We have a stand alone CO gas monitor (safety equipment) that uses a
>PIC16C74.
>If the power supply is momentarily shorted (milliseconds), the PIC does
>not recover, but locks up in random modes.
>We have the Watchdog timer ON and CLRWDT is only given one time in the
>main program loop.
>Any ideas? I was massacred today in an engineering meeting as this
>instrument was on the verge of its first major shipment.
James:
What type of oscillator are you using? TTL clock,crystal,etc. Is it still
oscillating after the power glitch? I mention this because if the program
counter (instruction pointer) is being loaded with garbage that is outside
your program loop, the watchdog timer should fire and reset the PIC unless
the clock/oscillator has stopped.
Any more info on what state it is locking up in? How long do you have to
power down to reset the processor? What value of bypass capacitors are on
the PIC?
Good luck,
Todd Peterson
===========================================================
*** Developers of the PICPlus(TM) Microcontroller Board ***
E-Mail Now for Your Free PICPlus(TM) Information Packet!
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===========================================================
> Here's a brain buster.
> We have a stand alone CO gas monitor (safety equipment) that uses a
> PIC16C74.
> If the power supply is momentarily shorted (milliseconds), the PIC does
> not recover, but locks up in random modes.
> We have the Watchdog timer ON and CLRWDT is only given one time in the
> main program loop.
> Any ideas? I was massacred today in an engineering meeting as this
> instrument was on the verge of its first major shipment.
> Thanks.
I think the biggest issue to watch for is the possibility that a power
glitch might have 'bizarre' effects on the PIC's registers without trashing
it totally. For example, if you set the TRIS registers on startup and never
again, they may get glitched without the program knowing it. If an input
becomes an output, the program could become "blind" to the true state of that
input; if an output becomes an input the program would, without knowing it,
become ineffectual at writing that pin.
This problem can be mitigated for some registers (like TRISA, TRISB, etc.)
by simply reloading the registers periodically. For other registers, things
may be a little harder. Your best bet is probably to have the program--just
after the CLRWDT--check the state of the system to ensure that it makes
sense. If you have some bytes to spare, it may be helpful to have a "second
order" software watchdog. If the software is supposed to do certain things in
response to certain events, you could create software counters/timers to
monitor such things. For example, if the system contains a modem which can
only answer the phone when not conducting a measurement (measurements should
normally take 5-15 seconds), a simple software watchdog could periodically
check the state of the phone ring signal. If the phone has rung five times
within a 45-second period, odds are really good that SOMETHING is going wrong
in the measurement routine.
Note that even with well-programmed software watchdogs, and a hardware watch-
dog to check for extreme conditions, power glitches can still cause system
problems. If your software can't deal acceptable with registers that get
garbled, you could consider a brownout-reset circuit. This will be much more
reliable than a watchdog at detecting errors resulting from glitches. It
won't, however, detect faults due to code glitches so a watchdog is still a
good idea.
> You could also write a macro at the end of your program
> which fills empty EEPROM with reset vectors.
Mike:
Bad idea.
First, it's unnecessary; the "empty" code-space is ALREADY filled
with instructions that won't affect program flow. The PC will just
increment through them until it wraps around to 0000 and hits the
reset vector.
Second, what will those "reset vectors" look like? Just a bunch of
GOTOs? How's that going to work on a processor whose code-space is
paged? Even if you're a little clever about this, it's unlikely that
your "solution" would be more reliable than simply leaving the unused
space in its erased state.
> >PIC16C74. If the power supply is momentarily shorted
> >(milliseconds), the PIC does not recover, but locks up in random
> >modes. We have the Watchdog timer ON and CLRWDT is only given one
> >time in the main program loop. Any ideas?
>
> if the program counter (instruction pointer) is being loaded with
> garbage that is outside your program loop, the watchdog timer
> should fire and reset the PIC unless the clock/oscillator has
> stopped.
Todd:
Wrong on both counts:
1. If the PIC's Vdd line drops below the operational threshold (3V
or so), but DOESN"T fall below 0.7V, the PIC will latch up when
power is restored, and the watchdog timer will NOT reset it.
2. Under normal circumstances, the watchdog timer works EVEN IF the
clock is stopped.
> 1. If the PIC's Vdd line drops below the operational threshold (3V
> or so), but DOESN"T fall below 0.7V, the PIC will latch up when
> power is restored, and the watchdog timer will NOT reset it.
By this, do you mean by the term "latchup", the "pseudo-SCR" latchup that
hits CMOS devices when their substrate junctions get biased into conduction?
If so, would using an LVI chip prevent it, or is it necessary to ensure that
power dips are always taken down to zero? I do know I once had a 16C84 chip
latch up on me (don't know why, but the chip was getting warm and drawing
150mA; powering the chip down and back again fixed it).
> > 1. If the PIC's Vdd line drops below the operational threshold
> > (3V or so), but DOESN"T fall below 0.7V, the PIC will latch up
> > when power is restored, and the watchdog timer will NOT reset it.
>
> By this, do you mean by the term "latchup", the "pseudo-SCR" latchup
> that hits CMOS devices when their substrate junctions get biased
> into conduction? If so, would using an LVI chip prevent it, or is it
> necessary to ensure that power dips are always taken down to zero?
John:
The "CMOS Latchup" problem you're describing DOES occasionally happen
(especially to the microprocessors on the PIC-Master emulator
probes), but it's unrelated to the specific problem I was discussing.
The "Brownout latchup" problem, as far as I know, is simply a symptom
of the PIC's logic circuitry starting to function at a lower voltage
than its RAM and EPROM circuitry. Those Motorola/Ricoh/Maxim
low-voltage-reset chips solve the problem nicely.
>First, it's unnecessary; the "empty" code-space is ALREADY filled
>with instructions that won't affect program flow.
Yes, but your program has to wait for the time it takes to
execute the number of (ADDLW ?) instructions, or the WDT timeout
if it is still responding, before the wrap-around. My
application involves the control of a high power system and
needs to respond immediately to a 'glitch' in the program
counter. We have brown-out and reset circuitry on-board, as
well as implementation of the WDT, but.... you never know.
>Second, what will those "reset vectors" look like? Just a bunch of
>GOTOs?
Yes, that's exactly what they are.
> How's that going to work on a
> processor whose code-space is paged?
Yes, you have a point, but it's a red-herring in the scope of
an already out-of control situtation. That is, your wrap-around will
only produce the same page result. If you have the macro loop detect
the first address in an empty page and put in a bit of code
to set the PCLATH register with the appropriate bits; The
GOTO which immediately follows would then vector off to the
appropriate reset address. Not perfect, but it gives you a
better statistical advantage of quickly regaining some
control over the application.
> >First, it's unnecessary; the "empty" code-space is ALREADY filled
> >with instructions that won't affect program flow.
>
> Yes, but your program has to wait for the time it takes to execute
> the number of (ADDLW ?) instructions, or the WDT timeout if it is
> still responding, before the wrap-around. My application ....
> needs to respond immediately to a 'glitch' in the program counter.
Mike:
We're talking about a couple of milliseconds. Surely that's
fast enough, especially considering the fact that the program's
out of control anyway.
> >Second, what will those "reset vectors" look like? Just a bunch of
> >GOTOs?
>
> Yes, that's exactly what they are.
>
> > How's that going to work on a processor whose code-space is paged?
>
> Yes, you have a point, but it's a red-herring in the scope of
> an already out-of control situtation. That is, your wrap-around will
> only produce the same page result.
Maybe I'm misunderstanding what you mean here, but I don't think
so. If the PC is allowed to execute all the instructions in the
"unused" space, it'll eventually wrap around to address 0000, on
page 0.
> If you have the macro loop detect the first address in an empty
> page and put in a bit of code to set the PCLATH register with the
> appropriate bits; The GOTO which immediately follows would then
> vector off to the appropriate reset address. Not perfect, but it
> gives you a better statistical advantage of quickly regaining some
> control over the application.
Better than what? Again, maybe I'm misunderstanding, but this
method would seem to work only if you could put the page-setting
instructions at the first location in EVERY page, including
those which are completely or partially used by your program.
If you were to do that, it would work just fine, but it's not
exactly the "use a macro to fill empty space with reset vectors"
solution that you originally proposed. Am I missing something,
or are you proposing a NEW solution?
> We're talking about a couple of milliseconds. Surely that's
> fast enough, especially considering the fact that the program's
> out of control anyway.
A couple of milliseconds at line frequencies, involving power
devices which are switching over 800W of power is quite
significant.
> Maybe I'm misunderstanding what you mean here, but I don't think
> so. If the PC is allowed to execute all the instructions in the
> "unused" space, it'll eventually wrap around to address 0000, on
> page 0.
Again, the issue is the time it takes to wrap-around. The following
program is an example of the macro (Which can be assembled, and tested
with MPSIM). The maximum time till the program delivers a reset
condition is only a few instructions. Forgive the previous post
which implied the "detection of page change". You have to manually
insert the few lines of code for the PCLATH modification to each page.
Regards,
Mike
----------------------------------------------------------------------
TITLE "Reset test program"
;
;
Processor 16C73
Radix HEX
EXPAND
;
PCLATH equ 0x0A
;
; Status register bits
;
CRY equ 0
DCRY equ 1
Z equ 2
PD equ 3
TO equ 4
RP0 equ 5
ORG 0x00
Start: nop
;
;
;*** Test Fault ****
bsf PCLATH,3
goto 0x900
;*******************
;
; your first page code goes here
;
fill (goto Start),0x800-$
;
;
ORG 0x800
bcf PCLATH,3
goto 0x00
;
; Any routines you want to add to this page go here
;
fill (goto 0x800),0x1000-$
END
Hi, a late reply that no one else seems to have directly suggested.
> We have a stand alone CO gas monitor (safety equipment) that uses a
> PIC16C74.
> If the power supply is momentarily shorted (milliseconds), the PIC does
> not recover, but locks up in random modes.
> We have the Watchdog timer ON and CLRWDT is only given one time in the
> main program loop.
Try to make the PIC get power before the attachments, so that you do not
have a Vin > VCC as this may cause some of the pins to possibly latch
up (speculation but also a requirement), this seems to be the only
mode that occurs from a power glitch instead of a normal power up from
cold. Your PIC may be working, just unable to talk.
Cheers
--
Kalle Pihlajasaari RemoveMEkallespamBeGonedata.co.za
Interface Products Box 15775, Doornfontein, 2028, South Africa
+27 (11) 402-7750 Fax: +27 (11) 402-7751
I've got an importante question to ask you all.
Is it possible to accelerate the init time of the power-on of the pics?
(pic 16c54 for exemple) I need an init time less than 1 ms.
I'm at the beginning of a new project, which involves controlling
of high power motors (+200W) to open/close train doors.
Most drivers seen (DC, brushless motors) are PWM-controlled.
Trying to use a PIC as the brain of the controller, I'd like
to hear from you what is the best option to choose.
What PIC would you select?
Perhaps some of you know about another type of drivers more
suitable to be used with microcontrollers.
What do you think all about? Are the PIC a reasonable choice?
I hope so.
Best regards,
Paco.
==================================================================
Francisco Rodriguez Ballester e-mail: spamBeGoneprodrigKILLspam@spam@aii.upv.es
Dept. DISCA, tlf: +(34)6 387 75 78
Univ. Politecnica de Valencia fax: +(34)6 387 95 79
c/Camino de Vera s/n, E-46071, VALENCIA (SPAIN)
==================================================================
> I've got an importante question to ask you all.
> Is it possible to accelerate the init time of the power-on of the pics?
> (pic 16c54 for exemple) I need an init time less than 1 ms.
If you use an RC oscillator, you can get a very fast reset time. Power-on
will still be limitted, but may still be better than with a crystal or
ceramic resonator.
On Fri, 26 Apr 1996 14:29:00, Francisco Rodriguez Ballester wrote:
>I'm at the beginning of a new project, which involves controlling
>of high power motors (+200W) to open/close train doors.
>What PIC would you select?
>Perhaps some of you know about another type of drivers more
>suitable to be used with microcontrollers.
There is no problem choosing a PIC to drive DC motor, I'm doing same with
other thing like: controlling DC motor in a R/C electrical plane.
The choice depend what you want to do. I think the best way is to choose a
PIC with INTERRUPT capabilities. You can also control current with a feed
back resistor and A/D converter. In my mind the best choice is a PIC16C71.
You can drive 200W DC motor with 4 or 6 Hi-Power MOS-FET and a speciallized
mos-fet driver.
>There is no problem choosing a PIC to drive DC motor, I'm doing same with
>other thing like: controlling DC motor in a R/C electrical plane.
>The choice depend what you want to do. I think the best way is to choose a
>PIC with INTERRUPT capabilities. You can also control current with a feed
>back resistor and A/D converter. In my mind the best choice is a PIC16C71.
>You can drive 200W DC motor with 4 or 6 Hi-Power MOS-FET and a speciallized
>mos-fet driver.
>
>Best regards,
> Philippe.
>
Hi Philippe,
Very interested to hear about the PIC being used for the speed
controller or perhaps soft start. I am very interested in electric flight,
I was even at the 94 F5B world champs and saw Tal Nizri fly, really
something to see. I think he is still flying and selling the CLASH, a real
nice plane.
Do you have any info on the circuit for a PIC based unit or is it the
British one. I have only seen ads for the British one, the author doesn't
seem to be interested in sharing the design.
Re the PIC based unit, myself and a friend (who is a bit of a PIC whiz) have
kicked the idea around of making a multiconfigurable unit but any help you
could give would be most appreciated.
Thanks Kim Turner.
> Very interested to hear about the PIC being used for the speed
>controller or perhaps soft start. I am very interested in electric flight,
>I was even at the 94 F5B world champs and saw Tal Nizri fly, really
>something to see. I think he is still flying and selling the CLASH, a real
>nice plane.
>Do you have any info on the circuit for a PIC based unit or is it the
>British one. I have only seen ads for the British one, the author doesn't
>seem to be interested in sharing the design.
>Re the PIC based unit, myself and a friend (who is a bit of a PIC whiz) have
>kicked the idea around of making a multiconfigurable unit but any help you
>could give would be most appreciated.
>Thanks Kim Turner.
As I'm always working ... I don't have so much time to do something else ...
I build glider, developp some programs ... and electronics cards ...
My last research on the "DC motor control subject" shows there are'nt
difficulties to build an electronic unit to drive motor.
I don't know if we talk about the same British PIC based unit, I saw the Ken
HEWITT schematic.
Anyway, I have done some experience with a SPEED600 (DC MOTOR for R/C
plane), a 7 elements battery pack and 3 MOSFET STP60N06. No problem for
thermal dissipation, loose voltage on MOS-FET is low, less than 0,2V, DC
current is about 12A.
STP60N06 have the following characteristic:
RDS_on = 0,02 OHM
ID (at 25degree) = 60 A
ID Max (pulse) = 240 A
Max POWER dissipation at 25 degree = 150W
VDS Max = 60V
This MOS-FET is available from: Radio Spare Componnent or FARNELL Components
in FRANCE.
If you decide to use another, there is no problem. You must be carrefull
about the RDS_ON parameter wich is the most important.
- To avoid reverse voltage, you must connect a fast diode, like TV Diode:
BYT xxxx or something else.
- to drive MOS-FET as fast as possible, it's necessary to use a MOS-FET
driver like:
EL 7242 or EL 7252 from ELANTEC (available from Radio-Spare Components)
or EL 7202 or EL 7212 from ELANTEC (available from Radio-Spare Components)
These drivers have TTL/MOS interface and needs only 5V to run.
- If you want to use this controller for a plane, it's better to put a break
circuit inside: means to put a MOS-FET directly on the motor to stop-it when
there is no more power. This seems to be a little bit dangerous, because you
must avoid to have at the same time:
- the power MOS-FET ON
- the break MOS-FET ON
In that case you risk a lot of smoke !!!
- PWM frequency to make a soft start seems to be around 2KHz as some
measurement on commercial unit shows it.
- In addition, you can make a PWM regulation of power to drive the motor, I
mean:
- MOTOR can be drove only at 7,2V for example (SPEED600 case)
- Battery voltage is 14 x 1,2V = 16,8V
To double the POWER time (normally a SPEED600 with 7 elements pack is about
3 minutes), and not destroy the motor by to high voltage and current, it's
possible to make a PWM regulation.
- getting and separate R/C signal is easy with interrupt possibilities (use
PIC16C71)
I already wrote code for 16C57 to get R/C signal.
Such a design seems to be not so hard to do, just a little bit long to
experiment. As I tell you, I don't have so much time and prefer to spend a
lot of money to buy a ready-to-plug unit (to put inside a glider). In
addition a little computation shows the commercial cost is lower than the
do-it-yourself cost, but making electronics board is not to earn money ...
only to have fun!
I was going through the Maplin Catalogue and came across a Single Chip Power
Supply. This may be an alternative to your transformer-less power supply unless
you want mains isolation. The chip is used together with a current limiting
resistor and can be connected to any AC supply from 28V to 264V and will give a
regulated output of 5V to 28V DC at up to 50mA. There are very few other
external components. The chip is made by Harris HV3-2405-5
I know the output current isn't much but it may solve some application problems.
In a an automotive powered circuit I am designing. I am concerned about
interfacing a switched positive power rail to an I/O port. For example.
When a stereo system provides a switched 12vdc rail, I want the PIC
to sense this, a very easy task. I assume I could simply use a
2 resistor-zener diode circuit to bring the 12v to 5v. Would such a simple
circuit provide the spike protection required to protect the pic?
I would appreciate any advice on interfacing such a power rail
to an I/O port. Thanks.
Seeking career in Instrumentation and Digital System Design
San Jose, California August 1996
www.acsu.buffalo.edu/~gandler/resume.html
______________________________________________________________________________
In a PIC controlled circuit, I would like to provide an auto reset
mode for the PIC during an undervoltage power supply situation, in order to
provide for a fail safe mode. The data books provide such a brownout
protection circuit. They also provide a circuit that compensates
for slow ramp up power supplies. My confusion is, how does one know if
their supply has a slow ramp up. There is no circuit listed that provides
slow ramp up compensation and brownout protection. Also, I know I have
seen inexpensive simple ICs that automatically activate an external
reset with a brownout condition, anyone know offhand of a chip #.
Seeking career in Instrumentation and Digital System Design
San Jose, California August 1996
www.acsu.buffalo.edu/~gandler/resume.html
______________________________________________________________________________
From:Neil Gandler
>Also, I know I have seen inexpensive simple ICs that automatically
>activate an external reset with a brownout condition,
>anyone know offhand of a chip #.
NEIL GANDLER wrote:
>
> In a an automotive powered circuit I am designing. I am concerned about
> interfacing a switched positive power rail to an I/O port. For example.
> When a stereo system provides a switched 12vdc rail, I want the PIC
> to sense this, a very easy task. I assume I could simply use a
> 2 resistor-zener diode circuit to bring the 12v to 5v. Would such a simple
> circuit provide the spike protection required to protect the pic?
> I would appreciate any advice on interfacing such a power rail
> to an I/O port. Thanks.
You don't need a Zener diode, a large resistor is sufficient. The port-pins
of the PICs have protection diodes to Gnd and Vcc. You only have to ensure,
that the current is lower than (I am not sure) 100 Micro-Amps. There
is an application note by Microchip, that tells something about that.
They even connect the PIC to 120 VAC.
>reset with a brownout condition, anyone know offhand of a chip #.
>
National Semiconductor LP2951 takes 0-30VDC input, regulates it to 5VDC @
100ma with a reset for your micro when 5V goes out of a 5% window.
8-pin DIP; less than a buck in quantity.
On your crystal question, with a conventional crystal or a ceramic
resonator, I typically use Zero ohms for series resistors. OTOH, I ALWAYS
use a 1 meg in parallel with the crystal or resonator for reliable startup.
If you're using a LF timing crystal like 32KHz, though, that's an entirely
different kind of animal.
.....................Reg Neale.....................
"Ignorance is a renewable resource" P.J. O'Rourke
For undervoltage reset, reset delay timer, watchdog timer, and battery backup
you can't beat the Maxxim MAX693, MAX800 and company.
For undervoltage reset with a delay timer and a watchdog (no battery backup),
the Dallas or Linear Tech DS1232 are tops. I have 68000 based stuff with the
DS1232. You can drag a screwdriver across the bottom of the PCB and it will
come right back up.
For undervoltage only, no watchdog, I like the Dallas DS1233 family in a TO-92
or SOT. They come in 3.3 and 5V. Motorola makes one, too, I think it is
MC34??? but I really don't remember. The Motorola is a simple comparator. It
doesn't have the time delay that the others have.
You might think an external watchdog has no value for the PIC since it has one
internally. Not so! The PIC watchdog is really only good for trapping errant
firmware or soft errors in the PC, etc. Also, I have had trouble with the PIC
locking up, including the watchdog, on brownouts. An external watchdog can cure
this ruggedly. You can even switch the power of the PIC with the watchdog and
recover from latch-up but that's getting carried away.
>You don't need a Zener diode, a large resistor is sufficient. The port-pins
>of the PICs have protection diodes to Gnd and Vcc. You only have to ensure,
>that the current is lower than (I am not sure) 100 Micro-Amps. There
>is an application note by Microchip, that tells something about that.
>They even connect the PIC to 120 VAC.
It's 500uA. I also use this technique to receive RS232 levels.
Good automotive practice is to expect up to 60V (from load dump) on the +12V
rail and gracefully handle down to 6V (cold crank). You can also see negative
voltages when someone hooks up the jumper cables backwards.
One other questions, I've been trying to get a MAXIM 770 Step up Power
Converter running from two "AA" Cells to +5V without much success. I've
tried to follow the datasheet for the "bootstrap" mode device.
I originally wanted to use the 756 device because it could be used to drive
the reset line of the PIC (and use the PWRTE), but I haven't had any luck
finding the devices. Does anybody know of any sources? Digi-Key doesn't
stock them and I can't find any local (Toronto) Sources.
Thanx,
Myke
Myke
"We're Starfleet officers, weird is part of the job."
I looked in mouser 1(800) 346-6873, they have dc-dc converters. I did
not spot a 3 to 5 v converter though. A call to them would surely get you
one though. I have asked for all sorts of stuff from them, and they seem
to always drag one up from somewhere.
>I've been trying to get a MAXIM 770 Step up
>Power Converter running from two "AA" Cells to +5V without
>much success.
Myke,
We here at Vicor have been trying to get MAXIM parts
in general with little success. You may try for a couple
of free samples, if you only need one or two. Linear
Technology, however, does have stock in most of their stuff.
You may want to try an LT1107, or something similar,
instead.
Mike Riendeau wrote:
>
> myke predko wrote:
>
> >I've been trying to get a MAXIM 770 Step up
> >Power Converter running from two "AA" Cells to +5V without
> >much success.
>
> Myke,
> We here at Vicor have been trying to get MAXIM parts
> in general with little success. You may try for a couple
> of free samples, if you only need one or two. Linear
> Technology, however, does have stock in most of their stuff.
> You may want to try an LT1107, or something similar,
> instead.
>
> MikeLinear offers a Nice software kit to
Calculate all kinds of power
supplies and automatically pics the best Regulator for the purpose and
Voltage and Current ratings. Its offered free of charge here so I assume
it will be for free everywhere.
Jattie van der Linde wrote
>Linear offers a Nice software kit to
>Calculate all kinds of power
>supplies and automatically pics the best Regulator for the purpose
>and Voltage and Current ratings. Its offered free of charge
>here so I assume it will be for free everywhere.
Yeah, I forgot to mention this. The program is called "SwitcherCAD".
It's DOS based and it's free.
Linear Technology
1630 McCarthy Blvd.
Milpitas, CA 95035-7487
(408) 432-1900
They may have a Web site with the software, but I don't know where
it is offhand.
Mike
MAXIM parts are extremely hard to get. I think I've called just about every
distributor on the continent.
Instead, I'm going with the Linear LT1111 5 Volt Regulator. It actually
requires fewer support components and is *much* easier to get (I've ordered
a bunch from Digi-Key).
Thanx for all the help and suggestions! They really got me out of a jam.
>Mike Riendeau wrote:
>>
>> myke predko wrote:
>>
>> >I've been trying to get a MAXIM 770 Step up
>> >Power Converter running from two "AA" Cells to +5V without
>> >much success.
>>
>> Myke,
>> We here at Vicor have been trying to get MAXIM parts
>> in general with little success. You may try for a couple
>> of free samples, if you only need one or two. Linear
>> Technology, however, does have stock in most of their stuff.
>> You may want to try an LT1107, or something similar,
>> instead.
>>
>> MikeLinear offers a Nice software kit to
> Calculate all kinds of power
>supplies and automatically pics the best Regulator for the purpose and
>Voltage and Current ratings. Its offered free of charge here so I assume
>it will be for free everywhere.
>
>Jattie.
>
>
Myke
"We're Starfleet officers, weird is part of the job."
> Hi Folks,
>
> One other questions, I've been trying to get a MAXIM 770 Step up Power
> Converter running from two "AA" Cells to +5V without much success. I've
> tried to follow the datasheet for the "bootstrap" mode device.
As Myke has bring up the topic of "Step Up Power Converter", I'd like to
know if any of you have use something that can boost maybe 4 AA ->
9V/12V... or 6 AA -> 12V.... etc...
LEUNG LAUREN KWAN-KIT wrote:
>
> Hi,
>
> On Tue, 11 Jun 1996, myke predko wrote:
>
> > Hi Folks,
> >
> > One other questions, I've been trying to get a MAXIM 770 Step up Power
> > Converter running from two "AA" Cells to +5V without much success. I've
> > tried to follow the datasheet for the "bootstrap" mode device.
>
> As Myke has bring up the topic of "Step Up Power Converter", I'd like to
> know if any of you have use something that can boost maybe 4 AA ->
> 9V/12V... or 6 AA -> 12V.... etc...
>
> - LaurenU can use the Linear Technology range.
> As Myke has bring up the topic of "Step Up Power Converter", I'd like to
> know if any of you have use something that can boost maybe 4 AA ->
> 9V/12V... or 6 AA -> 12V.... etc...
>
Hi,
It isn't too tough for small currents, a 7660, available from several
manufacturers, will give a nominal 9 volts from 4 cells and a nominal 12
volts from 6 cells. You will need to add two capacitors and probably a diode
too.
Voltage multipliers can get rather power hungry so if you have a spare PIC
output it's worth turning it off when you aren't using it.
For larger currents Astec offer a range of converter modules up to 6W which
offer 80% efficiency and convert 4.5-5.5 volts into 12V, 15V, +/- 12V or +/-
15V. I would expect several other manufacturers to offer similar modules
but these are available from Radiospares who probably have a subsidiary in
your area too.
Hope this is some help,
Keith.
==========================================================
Keith Dowsett "Variables won't; constants aren't."
> Jattie van der Linde wrote
> >Linear offers a Nice software kit to
> >Calculate all kinds of power
> >supplies and automatically pics the best Regulator for the purpose
> >and Voltage and Current ratings. Its offered free of charge
> >here so I assume it will be for free everywhere.
>
> Yeah, I forgot to mention this. The program is called "SwitcherCAD".
> It's DOS based and it's free.
>
> Linear Technology
> 1630 McCarthy Blvd.
> Milpitas, CA 95035-7487
> (408) 432-1900
>
> They may have a Web site with the software, but I don't know where
> it is offhand.
> Mike
>
Linear Tech. web site is at: http://www.linear-tech.com/
Eyal Oppenheimer
E-mail: eyalo@spam@aks.com
R&D
Aladdin Knowledge Systems Ltd.
Tel: +972-3-636-2222
Fax: +972-3-537-5796
WWW Home Page: http://www.aks.com
I'm having a bit of trouble with a program I am writing; I'm trying to wake
up from "sleep" with some inline code.
The sleep code I am using is simply:
clrwdt ; Use WDT for Wake Up
sleep
nop ; Make sure nothing potentiall unknown is
; Executed after "sleep"
When the WDT times out, or the interrupt executes, I seem to go back to
Address 0 with T0 PD both set (I verify this through the use of two LEDs
which show the value for these two bits).
The real purpose of this code is to be have a button press wake up the PIC.
I have just enabled the RB0/INT Pin (without setting the "GIE" bit) and this
does wake up the PIC from sleep, but also seems to reset the PIC.
As well, I tried setting a number of registers to a known value when the PIC
is active (before going to sleep) and then checking these values upon PIC
Reset (Execution at Address 0). These values seem to be randomized each
time the PIC goes to sleep.
Does anybody have any idea of what I'm doing wrong? I am expecting (and the
Data Sheet confirms this) that upon wake-up, I will continue executing from
the current PC (with PC+1 being the next address executed after Sleep), but
this is not happening. I'm also confused as to why the file Registers are
changing (because they seem to stay static, even if _MCLR is pulled low for
some time).
Thanx!
Myke
Do you ever feel like an XT Clone caught in the Pentium Pro Zone?
On Thu, 27 Jun 1996, myke predko wrote:
[...]
> The sleep code I am using is simply:
>
> clrwdt ; Use WDT for Wake Up
> sleep
> nop ; Make sure nothing potentiall unknown is
> ; Executed after "sleep"
>
> When the WDT times out, or the interrupt executes, I seem to go back to
> Address 0 with T0 PD both set (I verify this through the use of two LEDs
> which show the value for these two bits).
>
> The real purpose of this code is to be have a button press wake up the PIC.
> I have just enabled the RB0/INT Pin (without setting the "GIE" bit) and this
> does wake up the PIC from sleep, but also seems to reset the PIC.
>
> As well, I tried setting a number of registers to a known value when the PIC
> is active (before going to sleep) and then checking these values upon PIC
> Reset (Execution at Address 0). These values seem to be randomized each
> time the PIC goes to sleep.
First of all, the "clrwdt" instruction isn't necessary since entering
the power-down mode via the "sleep" instruction automatically clears
the watchdog timer.
If your watchdog timer times out, the PIC should reset... not continue.
That might explain why it's going to its reset vector (0x0000). Maybe
you should check what your watchdog's pre-scalar is?
You may also wish to read Microchip's "Errata Sheet" for whatever
type of PIC you're using. I know that I can't rely on the "PD" bit
of the PIC16C65 I'm using because the errata sheet says it may not
work right.
What seemed to be missing was some instruction to *clear* the RBIF
flag before going to sleep... For that matter, you'd better make
sure that *any* interrupt flags which are enabled have been cleared
before executing the "sleep" instruction.
> If your watchdog timer times out, the PIC should reset... not continue.
No, not necessarily. This is true for the 12 bit PICs, but not for the
14 bitters. Myke did not say what chip he is using, but if my guess
is right, he is using a 14 bit chip. The 14 bit chips have two different
behaviours for WDT timeout - in sleep mode it just wakes the chip up
and it resumes execution. In non-sleep mode it resets.
Myke, perhaps you are getting a WDT timeout _after_ the sleep has
"returned", and this is causing the reset? How do you handle a WDT
timeout when the key is *not* pressed?
In the seminar, we had some discussions on this. Rick Miller is correct in
that when you put it to sleep, the WDT will awake it and RESET it, just like
the WDT always does. There is one class of processors (don't remember if it
was just the high end) that if it gets an interupt, it will wake up and
continue on from where it goes to sleep. I would bet that you never wake up
from the interupt, but its always the WDT. Try disabling it when you reburn
the part and see if it executes correctly on the interupt. You have to
remember that the WDT is pretty fast (and it should be) to protect from going
into and executing bad code. If you are sitting around waiting for the button
to be pushed, and you are using the WDT, then you should probably put the
routine
at the reset org, look for the input and then go back to sleep.
As I said in my previous note, I set the Prescaler to the WDT and then
loaded the values with 0b0111 (which seems to give me the 2.3 sec delay that
it should according to 18 msec x 128). So, I don't think that I am getting
another reset with the WDT, but could the OPTION Register be reset (turning
back the WDT delay to 18msecs)?
Actually, thinking about it, this may be very possible because I have not
looked very closely at what is happening when the button is pressed (Yet
another case where I wished I had a scope at home). Componding the problem
is that I display the contents of STATUS and the button/WDT using LEDs, with
a looping delay before going back to sleep. Maybe the program is working
correctly, but the WDT is timing it back out and I can't see what's
happening. Although I did try turning off the WDT from the programmer,
maybe something else is happening (and something else for me to try).
>Rick Miller <RemoveMErickspam_OUTDigalogSys.com> wrote:
>
>> If your watchdog timer times out, the PIC should reset... not continue.
>
>No, not necessarily. This is true for the 12 bit PICs, but not for the
>14 bitters. Myke did not say what chip he is using, but if my guess
>is right, he is using a 14 bit chip. The 14 bit chips have two different
>behaviours for WDT timeout - in sleep mode it just wakes the chip up
>and it resumes execution. In non-sleep mode it resets.
>
>Myke, perhaps you are getting a WDT timeout _after_ the sleep has
>"returned", and this is causing the reset? How do you handle a WDT
>timeout when the key is *not* pressed?
>
>Clyde
>
>--
>Clyde Smith-Stubbs | HI-TECH Software, | Voice: +61 7 3300 5011
>clydespamhitech.com.au | P.O. Box 103, Alderley, | Fax: +61 7 3300 5246
>http://www.hitech.com.au | QLD, 4051, AUSTRALIA. | BBS: +61 7 3300 5235
>----------------------------------------------------------------------------
>For info on the World's best C cross compilers for embedded systems, point
>your WWW browser at http://www.hitech.com.au, or email spam_OUTinfospam_OUTspam_OUThitech.com.au
>
>
Do you ever feel like an XT Clone caught in the Pentium Pro Zone?
>
> How much current is feasible from a quad op-amp? Is high-voltage (24v) low-
> current easier than lower-voltage (5v) higher current?
>
You can get power op amps that will do about 15 amps - about 35 uk pounds.
There are quite a few companies selling opamps which can do about 2A that
have thermal shutdown etc etc for a lot less money. These are aimed at the
VCR type application of small motors.
Cheers,
David
--
===============================================================================
David Eastlake | dj-eastlspam_OUTuwe.ac.uk
InFACT Group | Extn: 2892 1D5
UWE | Tel: +44 117 9763861
Bristol | Fax: +44 117 9763852
BS16 1QY | zen.btc.uwe.ac.uk/Public/infact/david.html
UK | Robotics, Electronics and Sailing
===============================================================================
> I would like to develop a device to determine when someone walks into an
> area, the direction and speed of this person and possible the size of the
> person.
>
> What I am thinking of, which may be impossible, is to perform some crude
> image
> processing of an infrared image using a PIC or other
> microcontroller/processor. And passing this info to a PC.
There is a range of ideas promoted by the Lawrence Livermore national
laborotories in California.
The MIR sensors can detect moving bodies within well defined spaces
and can work through walls at wery low power without detection.
Unforturnately I have not been able to find any company that has licenced
the technology (very expensive) for use in motion detectors even though
it looks like it would be the killer application for all alarm systems.
If anyone knows of a company selling detectors using the MIR technology
then please let me/the list know about it.
The LLNL have also got on one of their pages a design that will allow
for location of a VR headset or Robot in a room using radio from multiple
beacons. I recall there was a call for this a year or so ago on the list
and could not remember the site, well dig around at the LLNL site and
send them e-mail, they do answer but are a bit cryptic.
Cheers
--
Kalle Pihlajasaari RemoveMEkalleKILLspam@spam@data.co.za
Interface Products Box 15775, Doornfontein, 2028, South Africa
+27 (11) 402-7750 Fax: +27 (11) 402-7751
> The MIR sensors can detect moving bodies within well defined spaces
> and can work through walls at wery low power without detection.
>
> Unforturnately I have not been able to find any company that has licenced
> the technology (very expensive) for use in motion detectors even though
> it looks like it would be the killer application for all alarm systems.
>
> If anyone knows of a company selling detectors using the MIR technology
> then please let me/the list know about it.
>
> The LLNL have also got on one of their pages a design that will allow
> for location of a VR headset or Robot in a room using radio from multiple
> beacons. I recall there was a call for this a year or so ago on the list
> and could not remember the site, well dig around at the LLNL site and
> send them e-mail, they do answer but are a bit cryptic.
>
Not sure if it is MIR but our maintanence guy has a stud sensor that
has a bar graph for relative distance through objects. Opened it up
and it was a single IC circuit with a stripline antenna etched in the
PcBd. The chip is marked ZIRCON 50761.
Can anyone please point me to any FAQ or home pages which may have code to use
the above PIC with a
PIC16C57.
For any unfamiliar with the device (Powertip PC-1602F1) its an 8 bit data/3 bit
control device, and
should be a piece of cake for anyone with micro experience (which I lack).
TIA,
Ken P.
You may need quite a load on the +5V output to
make sure the power supply is in regulation.
Of course your mileage may vary.
- -Mark
>>> Lauw Lim Un Tung <KILLspamtung.....PETER.PETRA.AC.ID> 30
July 1996 1:44 am >>>
I have 200 Watt PC Powersupply... I need to know
how much current it can
supply for +5V, -5V, +12V, and -12V.
Hi Luis,
I think what you are looking for has been published in a UK magazine called
Everyday Practical Electronics which features a lot of PIC designs. They
published a full article including PCB layouts and also you can send for a disc
of the software as well as buy the blank boards for a few UKP. It works out the
power consumed and will even tell you the cost of it.
There was some postings to the list from me and one or two others regarding this
around April this year. I've not got them anymore but have a look around in the
Piclist Archive. The magazine articles you need are in February and March 1996
issues.
PS Please dont be tempted by non isolated designs - you only got one life - at
least for now!
Bob Minchin wrote:
> ......
> PS Please dont be tempted by non isolated designs - you only got one life - at
> least for now!
I agree that hobbyists should avoid non-isolated designs. However, if
you are designing products for quantity production and cost counts,
there are ways to design non-isolated products, and you may as well know
that there are millions of them out there. For that matter, a
transformer is only as good as its insulation.
--
At 08:01 30-07-96 -0400, you wrote:
> +5V -5V +12V -12v
> --- ---- ---- ----
>150W 15A 0.5A 5A 0.5A
>180W 18A 0.5A 7A 0.5A
>200W 20A 0.5A 8A 0.5A
>230W 23A 0.5A 9A 0.5A
>250W 25A 0.5A 10A 0.5A
>
>You may need quite a load on the +5V output to
>make sure the power supply is in regulation.
>
>Of course your mileage may vary.
>
>- -Mark
No doubt about it, an old PC power supply would be great to run some PIC
projects but how do you 'fake' the 'power good' input, in my experience the
power supplies won't run without this feedback (orange wire I think).
Thanks Kim Turner.
Brad Turnert <KILLspambturnerspamBeGoneenterprise.powerup.com.au> wrote:
> No doubt about it, an old PC power supply would be great to run some PIC
> projects but how do you 'fake' the 'power good' input, in my experience the
> power supplies won't run without this feedback (orange wire I think).
I think you'll find the "power good" line is an *output* from the power supply -
I've regularly used PC power supplies without this line connected. Two things
to note; switching supplies in general only regulate properly with a minimum
load - a PIC probably won't draw this minimum so a loading resistor might be
a good idea; and if you want to use the +12 supply be aware it is often not
independently regulated and fluctuates quite a bit with overall power supply
load - it's only intended to power motors etc. where accurate regulation and
low power supply noise are not important.
--
Clyde Smith-Stubbs | HI-TECH Software, | Voice: +61 7 3300 5011 clydespamhitech.com.au | P.O. Box 103, Alderley, | Fax: +61 7 3300 5246 http://www.hitech.com.au | QLD, 4051, AUSTRALIA. | BBS: +61 7 3300 5235
---------------------------------------------------------------------------
For info on the World's best C cross compilers for embedded systems, point
your WWW browser at http://www.hitech.com.au, or email RemoveMEinfospamBeGoneRemoveMEhitech.com.au
> > +5V -5V +12V -12v
> > --- ---- ---- ----
> >150W 15A 0.5A 5A 0.5A
> >180W 18A 0.5A 7A 0.5A
> >200W 20A 0.5A 8A 0.5A
> >230W 23A 0.5A 9A 0.5A
> >250W 25A 0.5A 10A 0.5A
> >
> >You may need quite a load on the +5V output to
> >make sure the power supply is in regulation.
> >
> >Of course your mileage may vary.
> >
> >- -Mark
> No doubt about it, an old PC power supply would be great to run some PIC
> projects but how do you 'fake' the 'power good' input, in my experience the
> power supplies won't run without this feedback (orange wire I think).
As mentioned the PowerGood line is an output from the PSU
It is infact a very nice active low reset signal BUT it has very
limited drive capability on many PC supplies, I would put a 10K
resistor in series with it before trying to use it but you can
leave it open.
Loading should as suggested be done on the 5V line and 10% of the
rated power is usually safe. For the 150W supply you would need
1.5A which is 7.5W of dissapation (a 10W 3.3Ohm resistor will
do the trick nicely and you can fit it inside the PSU to the air
vent holes with some small screws, WARNING a lot of the heatsinks
inside the PSU are at mains potential so when you decide on a place
to put your load resistor do not allow it to get NEAR the other
components) so you can wire it up with a spare floppy power
lead onto the red and black wires and cut the other black and yellow
wire short at the PCB. You can also preload the +12 V supply
to improve the regulation using 5% of the rated load, the internal
fan is usually connected to the 12 V output as well. With the
150 W supply again you can use 0.25A giving 3W and a 5W 47 Ohm
resistor will do the trick.
The PowerGood line is suitable for driving a PIC MCLR pin with just
a resistor and it will hold the device in reset until the power
is stabilised. The basic stamp may not co-exist with the Powergood
signal but it has already got a small measure of reset circuitry
on board so I would ignore the PowerGood signal.
Cheers
--
Kalle Pihlajasaari KILLspamkallespamBeGonedata.co.za
Interface Products Box 15775, Doornfontein, 2028, South Africa
+27 (11) 402-7750 Fax: +27 (11) 402-7751
This has nothing to do with PIC, I'm afraid. Does anyone know if it's
possible to turn a typical switching power supply (constant voltage) into
a more-or-less constant current supply instead? Ideally, I'd like to take
something like a 5V 20A power supply and end up with an 8A constant current
supply (or similar.)
>This has nothing to do with PIC, I'm afraid. Does anyone know if it's
>possible to turn a typical switching power supply (constant voltage) into
>a more-or-less constant current supply instead? Ideally, I'd like to take
>something like a 5V 20A power supply and end up with an 8A constant current
>supply (or similar.)
>
>Thanks
>bill W
The short answer is yes.
The long answer depends on the SMPS controller and details of the
circuit.
I have recently completed a pic based constant current 15A/~3V
source using a PIC16C74 PWM output directly driving the FET and
the ADC for measuring current and voltage to switch from constant
current mode to constant voltage mode. The control loop runs at
10Khz which for this application was fast enough, and the slew
rate was limited in software. Detection of open circuit and
short circuit conditions. Effectively the 16C74 makes a flexible
albeit slow SMPS controller!.
Power Good is a status/control line. It is pulled up internally to
the supply. The PC motherboard monitors that line and will go into
POR if the line goes low. In old PC's, I used to connect a pushbutton
switch between Power Good and ground to get a reset switch which didn't
show up as a factory item for a couple of years. I'm talking early AT
days here.
Well in the olden days when you bought one of them
new fangled really fast IBM 6Mhz AT computers but
didn't order one of them huge high tech 5 1/4"
20Mb full height hard drives with 80mS access, it
shipped with a big power resistor that plugged
into the disk drive power connector. This used
enough current to keep the supply in regulation
and warm the box up too.
> +5V -5V +12V -12v
> --- ---- ---- ----
>150W 15A 0.5A 5A 0.5A
>180W 18A 0.5A 7A 0.5A
>200W 20A 0.5A 8A 0.5A
>230W 23A 0.5A 9A 0.5A
>250W 25A 0.5A 10A 0.5A
>
>You may need quite a load on the +5V output to
>make sure the power supply is in regulation.
>
>Of course your mileage may vary.
>
>- -Mark
No doubt about it, an old PC power supply would be
great to run some PIC
projects but how do you 'fake' the 'power good'
input, in my experience the
power supplies won't run without this feedback
(orange wire I think).
Thanks Kim Turner.
What do you think would be the best way to design a very low power 3V supply
? I need something that will provide some miliamps to my PIC circuit but
won't steal more than some microamps...
mestra@u-netsys.com.br (Engenharia Mestra de Sistemas Sociedade Ltda) wrote:
> What do you think would be the best way to design a very low power 3V supply
> ? I need something that will provide some miliamps to my PIC circuit but
> won't steal more than some microamps...
If you figure it out, the world's electricity generating authorities will kill
you.
A perpetual motion machine springs to mind...
I have in fact absolutely nothing useful to contribute on this question, other
than weak humor. Actually, that's not quite true. Maxim have a range of
switching regulators that might be worth looking at. I'm assuming you have
either a higher supply voltage that you want to regulate down with efficiency
(which the Maxim devices will do) or a low duty cycle (in which case a large
capacitor might be important).
>> What do you think would be the best way to design a very low power 3V supply
>> ? I need something that will provide some miliamps to my PIC circuit but
>> won't steal more than some microamps...
>
That's right, I meant efficiency, not the perpetual motion machine...
Maxim, as Clyde suggested, is a really good source of what you're
looking for. If you are looking at high quantity production, you may
want to check their lead times. About 8 months ago I was looking at
some of their parts, and they quoted 32 week lead times!
Another good source for this type of part is Linear Technology
(408-432-1900). You definitely want some type of switching capacitor
converter. They typicaly have > 95% power conversion efficiency.
> What do you think would be the best way to design a very low power 3V supply
> ? I need something that will provide some miliamps to my PIC circuit but
> won't steal more than some microamps...
If you figure it out, the world's electricity generating authorities will kill
you.
A perpetual motion machine springs to mind...
I have in fact absolutely nothing useful to contribute on this question, other
than weak humor. Actually, that's not quite true. Maxim have a range of
switching regulators that might be worth looking at. I'm assuming you have
either a higher supply voltage that you want to regulate down with efficiency
(which the Maxim devices will do) or a low duty cycle (in which case a large
capacitor might be important).
----------
> From: Engenharia Mestra de Sistemas Sociedade Ltda
> To: Multiple recipients of list PICLIST
> Subject: Low power 3V supply
> Date: Tuesday, August 06, 1996 2:29 AM
>
> Hi, fellow PICers.
>
>
> What do you think would be the best way to design a very low power 3V
supply
> ? I need something that will provide some miliamps to my PIC circuit but
> won't steal more than some microamps...
>
> TIA,
>
>
> Pedro Drummond
>
>
I selected an Analog Devices ADP3367 linear regular for a simular
project which uses 4 AA alkaline batterys as power source
Look at : http://www.analog.com/
For data sheets.
>Pedro Drummond. wrote:
> What do you think would be the best way to design a very low power 3V supply
> ? I need something that will provide some miliamps to my PIC circuit but
> won't steal more than some microamps...
I always recommend the Seiko linear regulators.
They make one that has 1.2 micro amp quiescent current!
S812xx series.
Hope this helps,
Gary Skinner, Electronic Solutions Inc
Design of custom control circuits
Denver CO 303-469-9322
Hi out there, I have not posed a question to this respected forum for a while.
I hope someone out there has an answer for me.
I am doing low power development and have been using the 16C65/JW (Eprom
version)
configured in LP mode and running it at 3V and 200KHz, basically at the edges of
the
mode. I have now gone through 10 chips all with the same problem. They start off
working fine and then after about 2 weeks they will not work at 3V and I can
only use
them from 5V and XT setting. The chips (I am told by the local supplier) have a
life
of 20-30 erases and I never reached that limit. They seem to be dying on me
faster
than they should. In fact if they died it would be one thing but they work at a
higher voltage.
Has anyone developed under these conditions i.e. 3V 200KHz or heard of similar
problems.
>I am doing low power development and have been using the 16C65/JW (Eprom
>version configured in LP mode and running it at 3V and 200KHz, basically at
the >edges of the mode. I have now gone through 10 chips all with the same
problem. >They start off working fine and then after about 2 weeks they will
not work at >3V and I can only use them from 5V and XT setting. The chips (I
am told by the >local supplier) have a life of 20-30 erases and I never
reached that limit.
>
>Moshe
This sounds like a problem with your programmer.
What programmer are you using? Is it verifying the programmed chip
at the correct operational voltages? (please tell me you are not
programming the chip at 5V?)
>At 03:25 PM 21/08/96 +0300, you wrote:
>
>>I am doing low power development and have been using the 16C65/JW (Eprom
>>version configured in LP mode and running it at 3V and 200KHz, basically at
>the >edges of the mode. I have now gone through 10 chips all with the same
>problem. >They start off working fine and then after about 2 weeks they will
>not work at >3V and I can only use them from 5V and XT setting. The chips (I
>am told by the >local supplier) have a life of 20-30 erases and I never
>reached that limit.
>>
>>Moshe
>
> This sounds like a problem with your programmer.
>
> What programmer are you using? Is it verifying the programmed chip
> at the correct operational voltages? (please tell me you are not
> programming the chip at 5V?)
>
>___Bob
>
The problem here is not that the programmer is failing to program correctly.
If that were the case then his "programmed" 0's would slowly migrate and
become 1's This migration would appear first at 5V and not at 3V. The fact
that the chips continue to work at 5V means his "programming margins," and
therefore programmer, are ok.
The problem is that the devices are not being FULLY ERASED before
programming. A 5V only programmer will not pick that up as the VDD min is
required to check the "erase margin." This is the only real _practical_
failure of a 5V only programmer. They suck if you are using the windowed
chips at a lower voltages.
Solutions: (to be followed religiously!)
Erase the devices for a whole hour before programming. DON'T EVER rely on
your 5V only programmer to check erase margins if using the parts at lower
voltages.
Cover the window at all times other than when erasing. This will prevent
slow erasure caused by the ambient light.
Consider using 16LC65s as they are rated to work at 3V. The standard parts
are rated to only a 4V minimum and this may also cause problems.
At 08:08 AM 8/23/96 -0500, you wrote:
>... They start off working fine and then after about 2 weeks they will
>>not work at >3V
This reminds me of a situation I experienced many years ago, with the
venerable 2708 EPROM. We had cases in which they would check out on our
Data I/O programmer, but would work unreliably in-circuit.
Turned out to have two causes (which Jim Robertson's email reminded me of):
both caused by our misguided but well-meaning technician. First, he noted
that the EPROMs would verfify as "erased" on the programer after far less
time under the UV than we normally specified. Second, he noted that the
EPROMS would verify as "programmed" after only a few seconds in the
programmer. So, he "saved time" by erasing the devices for only a few
minutes, and then interrupting the programming cycle very early on.
Of course, neither case was valid: the devices were neother adequately
erased,nor were they fully porgrammed, causing unold problems until we
determined the cause! It was a case of misplaced ingenuity.
About a month ago there was thread about using PC power supplies as benchtop power supplies. Could someone send me some of that information or direct me to a source.
I'm working now on a project using PIC16C84, and I have some problems
with the power feeding.
A point in the problem specification is that in the case of power
failure the product has to be able to restore the previous status and to
continue his job. All seems to be simple: store the status in data EEPROM
and restore it on reset.
If the power failure is longer than aprox. 1 sec. everything is ok, but
my system die if the power failure is shorter! I'm using WDT, but it
seems to be ineffective for this situation.
Is there anybody who can give me some advice?
Thanks,
Dan
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dan-Victor RUSU Technical University of Cluj
Computer Science Department EraseMErdvRemoveMEutcluj.ro Baritiu, 26 Cluj-Napoca, ROMANIA http://www.utcluj.ro/~rdv Fax: (+40) 64 194491
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>I'm working now on a project using PIC16C84, and I have some problems
>with the power feeding.
>
>If the power failure is longer than aprox. 1 sec. everything is ok, but
>my system die if the power failure is shorter! I'm using WDT, but it
>seems to be ineffective for this situation.
This sounds like a brown-out problem.
If the reset pin doesn't go all the way to ground the
PIC will lock-up, and not recover until it sees a power
cycle.
You should try adding a hard reset circuit. A MAX701
is a simple and cheap place to start.
I have a prototype circuit that, about 75% of the time, does not do a
proper power-on reset. The power supply is a wall-wart transformer with a
10uF cap across the leads ffeding a 7805 regulator with a 100uF cap across
+5V and gnd. (The capacitor values were chosen by the scientific method of
looking into the junkbox and picking out what was in there)
Is there a small, cheap external circuit I can build to guarantee a
power-on reset?
Thanks,
-Matt
"DOS Computers manufactured by companies such as IBM, Compaq, Tandy, and
millions of others are by far the most popular, with about 70 million
machines in use wordwide. Macintosh fans, on the other hand, may note that
cockroaches are far more numerous than humans, and that numbers alone do
not denote a higher life form."
> I'm working now on a project using PIC16C84, and I have some
> problems with the power feeding.
>
> A point in the problem specification is that in the case of
> power failure the product has to be able to restore the
> previous status and to continue his job. All seems to be
> simple: store the status in data EEPROM and restore it on
> reset.
>
> If the power failure is longer than aprox. 1 sec. everything
> is ok, but my system die if the power failure is shorter!
Dan:
To my mind you use the simple RC to reset the PIC and your
capicitor does not discharging during the power failure.
Try to use a diode from reset (+) to power (-).
Or use a special chip - MAXIMs or Analog Devices.
Best Wishes, Alex Torres.
Kharkov, Ukraine, exUSSR.
E-Mail To : spamaltor.....spamcook.kharkov.ua via InterNet
or 2:461/28 via FidoNet
Matthew Mucker wrote:
>
> I have a prototype circuit that, about 75% of the time, does not do a
> proper power-on reset. The power supply is a wall-wart transformer with a
> 10uF cap across the leads ffeding a 7805 regulator with a 100uF cap across
> +5V and gnd. (The capacitor values were chosen by the scientific method of
> looking into the junkbox and picking out what was in there)
>
> Is there a small, cheap external circuit I can build to guarantee a
> power-on reset?
>
> Thanks,
> -Matt
The databooks contain a number of circuits, ranging from cheap to
effective.
--
Friendly Regards
Tjaart van der Walt
______________________________________________________________
| Another sun-deprived R&D Engineer slaving away in a dungeon |
|WASP International GSM vehicle tracking and datacomm solutions|
| +27-(0)11-622-8686 | http://wasp.co.za |
|______________________________________________________________|
> Is there a small, cheap external circuit I can build to guarantee a
> power-on reset?
Yes, but if you tell us what you have hanging off the /MCLR pin
right now, it might be easier to suggest what to do next. Also,
why not put the bigger (100uF) cap on the *input* to the 7805 and
the smaller one on the output? There's no reason why you should need
100uF on the 5V rail.
> > I'm working now on a project using PIC16C84, and I have some
> > problems with the power feeding.
> >
> > A point in the problem specification is that in the case of
> > power failure the product has to be able to restore the
> > previous status and to continue his job. All seems to be
> > simple: store the status in data EEPROM and restore it on
> > reset.
> >
> > If the power failure is longer than aprox. 1 sec. everything
> > is ok, but my system die if the power failure is shorter!
>
> Dan:
>
> To my mind you use the simple RC to reset the PIC and your
> capicitor does not discharging during the power failure.
> Try to use a diode from reset (+) to power (-).
> Or use a special chip - MAXIMs or Analog Devices.
>
I'm using the MCLR pin for in circuit programming. The power on reset is
performed by PIC16C84 internal power on reset circuit. I'm also using the
internal power on reset timer.
Matthew Mucker wrote:
>
> I have a prototype circuit that, about 75% of the time, does not do a
> proper power-on reset. The power supply is a wall-wart transformer with a
> 10uF cap across the leads ffeding a 7805 regulator with a 100uF cap across
> +5V and gnd. (The capacitor values were chosen by the scientific method of
> looking into the junkbox and picking out what was in there)
>
> Is there a small, cheap external circuit I can build to guarantee a
> power-on reset?
>
> Thanks,
> -Matt
There are lots of devices designed for doing just this. Some cheap, some
not so cheap.
Try the Panasonic MN1381-S. This is possibly the cheapest version in a
TO-92 package. It rates a mention in the Oct-96 edition of Nuts and
Volts, and basic data can be found in the current Digi-Key catalogue. A
3 wire cct. VCC, GND and reset. Forces a low reset if the voltage is
detected in a specified range.
EASY PIC'n Beginners Guide to using PIC 16/17 MicroChip products.
Picosaurus(tm) 40 pin FED Basic with 8 channels of A-D, and real Uart.
MEL PicBasic Compiler. Programmers from 15 USD. Pic-Axe(tm) A New Tool.
I've had similar problems with all of my pic projects, the hardware solution
is a Motorola part MC33064 reset chip, three leads in a transistor package.
This is fairly reliable, 98% of the time. Using the watchdog timer seems to be
the software solution and is reliable. The power supply is not the issue, I
use $200
Hammond power supplies and the problem still occurs. If the POR fails then the
watchdog will bring it up after the timeout.
>I have a prototype circuit that, about 75% of the time, does not do a
>proper power-on reset. The power supply is a wall-wart transformer with a
>10uF cap across the leads ffeding a 7805 regulator with a 100uF cap across
>+5V and gnd. (The capacitor values were chosen by the scientific method of
>looking into the junkbox and picking out what was in there)
>
>Is there a small, cheap external circuit I can build to guarantee a
>power-on reset?
>
>Thanks,
> -Matt
>
>
> "DOS Computers manufactured by companies such as IBM, Compaq, Tandy, and
>millions of others are by far the most popular, with about 70 million
>machines in use wordwide. Macintosh fans, on the other hand, may note that
>cockroaches are far more numerous than humans, and that numbers alone do
>not denote a higher life form."
>
>
The root cause of the failure to reset is that the 5V supply is not
decaying far enough to reset the chip.
With the 16C5x parts, the built-in POR circuit is guaranteed to work
only if the initial Vdd voltage is ZERO. From what I've found,
applying power when the supply has decayed to about 1.5 volts will
usually result in the processor coming up in a random state.
If short power outages are a problem, you should ensure that the Vdd
(or MCLR pin, if not connected to Vdd) is pulled down to virtually
zero when the power supply source turns off. Put shortly, add a
brown-out reset circuit.
I've done this on one circuit by connecting a P-channel JFET across
the 5V supply with the gate connected to the unregulated supply, which
is typically > 9V when on. The JFET chosen has a pinch-off threshold
of about 6-8 volts, so that the JFET remains off as long as the power
supply is active, but turns on when the unregulated supply falls below
the transistor threshold. When the JFET turns on, it quickly
discharges the 5V filter capacitance.
If adding a little more money isn't a problem, one of the suggested
external reset circuits would take care of your difficulty.
100uF is a lot of capacitance to have on the 5V supply. I also agree
that the 100uF should be on the unregulated supply and the 10uF on the
5V supply. This change alone may improve the reliability of reset.
>I have a prototype circuit that, about 75% of the time, does not do a
>proper power-on reset. The power supply is a wall-wart transformer with a
>10uF cap across the leads ffeding a 7805 regulator with a 100uF cap across
>+5V and gnd. (The capacitor values were chosen by the scientific method of
>looking into the junkbox and picking out what was in there)
>
>Is there a small, cheap external circuit I can build to guarantee a
>power-on reset?
>
>Thanks,
> -Matt
>
>Matthew Mucker <RemoveMEmmuckerKILLspamRemoveMEAIRMAIL.NET> wrote:
>
>> Is there a small, cheap external circuit I can build to guarantee a
>> power-on reset?
>
>Yes, but if you tell us what you have hanging off the /MCLR pin
>right now, it might be easier to suggest what to do next. Also,
>why not put the bigger (100uF) cap on the *input* to the 7805 and
>the smaller one on the output? There's no reason why you should need
>100uF on the 5V rail.
>
>Clyde
>
Matthew,
I typically use your type of circuit, without brownout protection, so the
problem is soluable.
I agree with Clyde, you should not have a 100 uF cap on your Vdd Rail - this
will slow down your power up, which will cause restart problems. I use 10
uF caps on both sides of the 7805.
As Clyde said, you should also check how _MCLR is connected. I usually
attach it to Vdd through a 4.7K resistor. This way, to reset the circuit, I
just have to short _MCLR and Vss (adjacent) pins with a screw driver.
Lastly, have you turned on the PWRTE Bit in the configuration file? This
will delay powerup by 70 ms (approx) for the Power to stabilize.
Avoiding precedents does not mean nothing should ever be done. It only
means that nothing should ever be done for the first time - Sir Humphrey
Appleby K.C.B.
>> Is there a small, cheap external circuit I can build to guarantee a
>> power-on reset?
>
>Yes, but if you tell us what you have hanging off the /MCLR pin
>right now, it might be easier to suggest what to do next. Also,
>why not put the bigger (100uF) cap on the *input* to the 7805 and
>the smaller one on the output? There's no reason why you should need
>100uF on the 5V rail.
!MCLR is tied to +5V. I only have the condensed data sheets that Parallax
sends with their stuff, so I don't really know all that I should here.
Obviously.
-Matt
"DOS Computers manufactured by companies such as IBM, Compaq, Tandy, and
millions of others are by far the most popular, with about 70 million
machines in use wordwide. Macintosh fans, on the other hand, may note that
cockroaches are far more numerous than humans, and that numbers alone do
not denote a higher life form."
> !MCLR is tied to +5V. I only have the condensed data sheets that Parallax
> sends with their stuff, so I don't really know all that I should here.
Ok, then all you probably need is to take a 100K resistor from VCC,
paralleled with a diode, connected to a 1uF tantalum cap to ground. Connect
/MCLR to the junction, e.g.
The diode can be a 1N914 or equivalent. You should find this will give a solid
power-on reset. It won't give total brownout protection, but it should be
quite good enough. The diode is reverse-biased while operating, but dischages
the cap quickly when power is removed.
Clyde
--
Clyde Smith-Stubbs | HI-TECH Software, | Voice: +61 7 3354 2411 spamclydehitech.com.au | P.O. Box 103, Alderley, | Fax: +61 7 3354 2422 http://www.hitech.com.au | QLD, 4051, AUSTRALIA. |
---------------------------------------------------------------------------
For info on the World's best C cross compilers for embedded systems, point
your WWW browser at http://www.hitech.com.au, or email infoSTOPspamhitech.com.au
>I have a prototype circuit that, about 75% of the time, does not do a
>proper power-on reset. The power supply is a wall-wart transformer with a
>10uF cap across the leads ffeding a 7805 regulator with a 100uF cap across
>+5V and gnd.
Just for fun, try putting a 220 ohm resistor accross the input filter cap.
PICs can lock up if the power supply voltsge does not collapse below 0.6 Vdc
or so. Your filter cap can hold at that voltage for days. Thanks to Andrew
Warren for helping me out with exactly that problem a couple of years ago.
I have a PIC project that I would like to use I2C to communincate between
several PIC's. I would like to keep the connections to three wires DATA
CLOCK and GND. I have heard that devices can be powered from the I2C bus.
What is the best way to do this with the PIC?
I need to measure a continuous frequency between 0 - 250 cycles/MINUTE,
and transmit it via RS-232 at 2400 baud in a message containing 6 bytes
once 5 seconds.
The PIC I plan to use is the low power 84 variant, running at 32 KHz,
if possible.
The two separate requirements are easy to implement on their own, it's
getting the PIC to implement them concurrently that I'm having trouble
with. I need to continue measuring the input frequency even while I am
transmitting the output message.
I'd appreciate it if anybody who has solved this type of problem, can
give me a few pointers as this type of task, measure an input and
transmit it must be quite common.
With the PIC running at 32KHz, it is only operating at 8K instructions
per second. Transmitting at 2400 baud, there is time for only 7
instructions per bit.
I been tossing ideas around for a number of months now with no real
solution comming forward. I could use 2 Pics, one to do the counting,
the other to do the transmitting, but then I might as well use a
faster crystal.
Are there other alternatives? I may be blinkered down a set path.
Any input would be great. Code fragments would be fantastic.
Thanks guys,
Peter.
--
_______________________________________________________________________
Peter Homann email: peterhSTOPspamKILLspamadacel.com.au Work : +61 3 9596-2991
Adacel Pty Ltd Fax : +61 3 9596-2960
250 Bay St, Brighton 3186, VIC, AUSTRALIA Mobile : 014 025-925
>I need to measure a continuous frequency between 0 - 250 cycles/MINUTE,
>and transmit it via RS-232 at 2400 baud in a message containing 6 bytes
>once 5 seconds.
Peter, what's the six-byte message you send?
(I want to get a handle on the processing required to
create the message string.)
>
> Hi,
>
> I need to measure a continuous frequency between 0 - 250 cycles/MINUTE,
> and transmit it via RS-232 at 2400 baud in a message containing 6 bytes
> once 5 seconds.
>
> The PIC I plan to use is the low power 84 variant, running at 32 KHz,
> if possible.
>
> The two separate requirements are easy to implement on their own, it's
> getting the PIC to implement them concurrently that I'm having trouble
> with. I need to continue measuring the input frequency even while I am
> transmitting the output message.
>
> I'd appreciate it if anybody who has solved this type of problem, can
> give me a few pointers as this type of task, measure an input and
> transmit it must be quite common.
>
> With the PIC running at 32KHz, it is only operating at 8K instructions
> per second. Transmitting at 2400 baud, there is time for only 7
> instructions per bit.
>
> I been tossing ideas around for a number of months now with no real
> solution comming forward. I could use 2 Pics, one to do the counting,
> the other to do the transmitting, but then I might as well use a
> faster crystal.
>
> Are there other alternatives? I may be blinkered down a set path.
>
> Any input would be great. Code fragments would be fantastic.
>
> Thanks guys,
>
> Peter.
> --
> _______________________________________________________________________
> Peter Homann email: @spam@peterh.....spamadacel.com.au Work : +61 3 9596-2991
> Adacel Pty Ltd Fax : +61 3 9596-2960
> 250 Bay St, Brighton 3186, VIC, AUSTRALIA Mobile : 014 025-925
Hi, I have been working on a system that counts pulses and pulse width
using the 84 .I use both the T0 clock and INT on portB0 to generate
ints.
If you set the ints up so that an int is generated on the rising edge of
portb0 and increment a counter every time an int is generated you can
count pulses. now if you also set the clock to generate an int at a set
duty cycle you can count the number of pulses on the portb0 pin within a
set time. all of this can be done in the background and due to the
nature of the ints it is also VERY presise.
>With the PIC running at 32KHz, it is only operating at 8K instructions
>per second. Transmitting at 2400 baud, there is time for only 7
>instructions per bit.
>I need to measure a continuous frequency between 0 - 250 cycles/MINUTE,
>and transmit it via RS-232 at 2400 baud in a message containing 6 bytes
>once 5 seconds.
>
>The PIC I plan to use is the low power 84 variant, running at 32 KHz,
>if possible.
Peter, you don't indicate the accuracy with which you need
to measure the frequency...
However, with a 32.768 kHz clock (which is 8192 instructions
per second) a variation of one instruction in detecting the
edge of a 250 rpm signal will cause an error in the calculated
instantaneous frequency of 0.2 rpm.
Assuming you don't want your measurement to be much less
accurate than this, you must measure the edges of the input
signal to within an instruction time.
You can do this by setting up TMR0 as a free running timer
with no prescale, configuring RB0 as an interrupt, and
connecting your input signal to RB0.
On each rising edge you get an interrupt, and in your ISR
you capture TMR0.
You must handle overflow of TMR0 in your main line code.
You are now measuring your signal period, and thus your
signal frequency, as accurately as it is possible.
Ok, now to the output side of the equation...
I can solve your problem if I can change your requirements :-)
Use 300 baud instead of 2400 baud (which is barely possible
anyway).
At 300 baud you have just over 27 instructions per bit. The
ISR to capture TMR0 should be six instructions. This interrupt
can never occur more than once per character (indeed, can never
occur more than once per six byte transmission). Stretching
a single bit time by 20% will _probably_ be ok...
Don't forget to handle TMR0 overflow between each byte.
Robert Lunn wrote:
>
> >I need to measure a continuous frequency between 0 - 250 cycles/MINUTE,
> >and transmit it via RS-232 at 2400 baud in a message containing 6 bytes
> >once 5 seconds.
>
> Peter, what's the six-byte message you send?
>
> (I want to get a handle on the processing required to
> create the message string.)
>
> ___Bob
Bob, you could try setting up an array of say 6 bytes in memory
where the first would be an STX byte the next four would be the ascii of
the 4 digit number and the last being EOT so a value 123 would be
<stx><0><1><2><3><eot> or in hex 033031323304 this way the stx will
indicate the start of the numeric string and the eot the end. the
receiving equipment would be able to take the val of the four digits
using an ascii to int conversion. if the interupt code updates the bytes
of the output string then all you have to do is just keep sending it out
every 5 seconds or so.
>>I need to measure a continuous frequency between 0 - 250 cycles/MINUTE,
>>and transmit it via RS-232 at 2400 baud in a message containing 6 bytes
>>once 5 seconds.
>>
>>The PIC I plan to use is the low power 84 variant, running at 32 KHz,
>>if possible.
>
> On each rising edge you get an interrupt, and in your ISR
> you capture TMR0.
>
> At 300 baud you have just over 27 instructions per bit. The
> ISR to capture TMR0 should be six instructions.
I was a bit quite of the mark. The ISR _is_ six instructions,
but it executes in _seven_ cycles (because of the RETFI). Also,
there are two cycles spent getting into the ISR.
That's a total of NINE cycles.
This is a 30% error in bit timing. At 300 baud I still think
this will work (hopeful grin). And because the bit timing is
27.3 instructions rather than 27, you do make up a couple of
cycles if the interrupt occurs early in the transmitted byte.
>
> Peter Homann wrote:
> >
> > Hi,
> >
> > I need to measure a continuous frequency between 0 - 250 cycles/MINUTE,
> > and transmit it via RS-232 at 2400 baud in a message containing 6 bytes
> > once 5 seconds.
> >
> > The PIC I plan to use is the low power 84 variant, running at 32 KHz,
> > if possible.
> >
> > The two separate requirements are easy to implement on their own, it's
> > getting the PIC to implement them concurrently that I'm having trouble
> > with. I need to continue measuring the input frequency even while I am
> > transmitting the output message.
> >
> > I'd appreciate it if anybody who has solved this type of problem, can
> > give me a few pointers as this type of task, measure an input and
> > transmit it must be quite common.
> >
> > With the PIC running at 32KHz, it is only operating at 8K instructions
> > per second. Transmitting at 2400 baud, there is time for only 7
> > instructions per bit.
> >
> > I been tossing ideas around for a number of months now with no real
> > solution comming forward. I could use 2 Pics, one to do the counting,
> > the other to do the transmitting, but then I might as well use a
> > faster crystal.
> >
> > Are there other alternatives? I may be blinkered down a set path.
> >
> > Any input would be great. Code fragments would be fantastic.
> >
> > Thanks guys,
> >
> > Peter.
> > --
> > _______________________________________________________________________> >
> > Adacel Pty Ltd Fax : +61 3 9596-2960
> > 250 Bay St, Brighton 3186, VIC, AUSTRALIA Mobile : 014 025-925
>
> Hi, I have been working on a system that counts pulses and pulse width
> using the 84 .I use both the T0 clock and INT on portB0 to generate
> ints.
> If you set the ints up so that an int is generated on the rising edge of
> portb0 and increment a counter every time an int is generated you can
> count pulses. now if you also set the clock to generate an int at a set
> duty cycle you can count the number of pulses on the portb0 pin within a
> set time. all of this can be done in the background and due to the
> nature of the ints it is also VERY presise.
>
> I hope this is of some use
>
> Peter........
I think Peter solution is good. In order to improve it you program the
interrupt to be generated in the rising edge and during the int you put
a timer running and program the int for the complementary edge (if it
was up edge turns to down edge and vice-versa), you can get know
information about dutty-cycle and frequency and you can estimate the
frequency with more precision.
Don't know why you need to use 32 kHz --- likely to save power.
One thought. You need a higher clock speed to transmit at 2400 baud. I
don't know if this would work, but you could have two external clocks
... one at 32 kHz and one at an appropriate higher rate for the 2400
baud stuff. Use a gate controlled by a pin on the PIC to switch clock
speeds to the higher one when you need to send the 6 bytes of data at
2400 baud, the switch back to the slower clock.
It would require some testing to see if the clock speed switch is
practicle or not.
>----------
>From: Peter Homann[SMTP:peterh.....ADACEL.COM.AU]
>Sent: Tuesday, November 05, 1996 7:20 PM
>To: Multiple recipients of list PICLIST
>Subject: Concurrency Problem on a low power PIC 84
>
>Hi,
>
>I need to measure a continuous frequency between 0 - 250 cycles/MINUTE,
>and transmit it via RS-232 at 2400 baud in a message containing 6 bytes
>once 5 seconds.
>
>The PIC I plan to use is the low power 84 variant, running at 32 KHz,
>if possible.
> (stuff deleted)
Robert Lunn wrote:
>
> >I need to measure a continuous frequency between 0 - 250 cycles/MINUTE,
> >and transmit it via RS-232 at 2400 baud in a message containing 6 bytes
> >once 5 seconds.
>
> Peter, what's the six-byte message you send?
>
> (I want to get a handle on the processing required to
> create the message string.)
Bob,
Sorry, but there are only five bytes and are as follows;
Byte Description
-----------------------------------------------------------------
1 Start of Message ID Constant
2-3 Unit Identification 15 bits constant (1 bit battery low)
4 Frequency Value Variable
5 Checksum Variable
Sorry for the delay in answering, and thanks for your interest.
Regards,
Peter
--
_______________________________________________________________________
Peter Homann email: KILLspampeterhspam_OUTadacel.com.au Work : +61 3 9596-2991
Adacel Pty Ltd Fax : +61 3 9596-2960
250 Bay St, Brighton 3186, VIC, AUSTRALIA Mobile : 014 025-925
Amberdrew Ltd wrote:
>
> Robert Lunn wrote:
> >
> > >I need to measure a continuous frequency between 0 - 250
cycles/MINUTE,
> > >and transmit it via RS-232 at 2400 baud in a message containing 6
bytes
> > >once 5 seconds.
> >
> > Peter, what's the six-byte message you send?
> >
> > (I want to get a handle on the processing required to
> > create the message string.)
> >
> > ___Bob
>
> Bob, you could try setting up an array of say 6 bytes in memory
> where the first would be an STX byte the next four would be the ascii
of
> the 4 digit number and the last being EOT so a value 123 would be
> <stx><0><1><2><3><eot> or in hex 033031323304 this way the stx will
> indicate the start of the numeric string and the eot the end. the
> receiving equipment would be able to take the val of the four digits
> using an ascii to int conversion. if the interupt code updates the
bytes
> of the output string then all you have to do is just keep sending it
out
> every 5 seconds or so.
>
> Peter .......
Peter,
Is not the problem with this method the fact that while the message
is being 'bit banged' out, the interrupt may occur, screwing up the
serial data stream?
Peter.
--
_______________________________________________________________________
Peter Homann email: spam_OUTpeterhTakeThisOuTadacel.com.au Work : +61 3 9596-2991
Adacel Pty Ltd Fax : +61 3 9596-2960
250 Bay St, Brighton 3186, VIC, AUSTRALIA Mobile : 014 025-925
Robert Lunn wrote:
>
> >With the PIC running at 32KHz, it is only operating at 8K instructions
> >per second. Transmitting at 2400 baud, there is time for only 7
> >instructions per bit.
>
> Ah, isn't that 3.4 instructions per bit?
>
> ___Bob
Yep, looks like the data rate will be slower, 1200 maybe.
Peter.
--
_______________________________________________________________________
Peter Homann email: .....peterh.....RemoveMEadacel.com.au Work : +61 3 9596-2991
Adacel Pty Ltd Fax : +61 3 9596-2960
250 Bay St, Brighton 3186, VIC, AUSTRALIA Mobile : 014 025-925
>
> Peter Homann wrote:
> >
> > Hi,
> >
> > I need to measure a continuous frequency between 0 - 250 cycles/MINUTE,
> > and transmit it via RS-232 at 2400 baud in a message containing 6 bytes
> > once 5 seconds.
> >
> > The PIC I plan to use is the low power 84 variant, running at 32 KHz,
> > if possible.
> >
> > The two separate requirements are easy to implement on their own, it's
> > getting the PIC to implement them concurrently that I'm having trouble
> > with. I need to continue measuring the input frequency even while I am
> > transmitting the output message.
> >
> > I'd appreciate it if anybody who has solved this type of problem, can
> > give me a few pointers as this type of task, measure an input and
> > transmit it must be quite common.
> >
> > With the PIC running at 32KHz, it is only operating at 8K instructions
> > per second. Transmitting at 2400 baud, there is time for only 7
> > instructions per bit.
> >
> > I been tossing ideas around for a number of months now with no real
> > solution comming forward. I could use 2 Pics, one to do the counting,
> > the other to do the transmitting, but then I might as well use a
> > faster crystal.
> >
> > Are there other alternatives? I may be blinkered down a set path.
> >
> > Any input would be great. Code fragments would be fantastic.
> >
> > Thanks guys,
> >
> > Peter.
> > --
> > _______________________________________________________________________
> > Peter Homann email: spam_OUTpeterhTakeThisOuTEraseMEadacel.com.au Work : +61 3 9596-2991
> > Adacel Pty Ltd Fax : +61 3 9596-2960
> > 250 Bay St, Brighton 3186, VIC, AUSTRALIA Mobile : 014 025-925
>
> Hi, I have been working on a system that counts pulses and pulse width
> using the 84 .I use both the T0 clock and INT on portB0 to generate
> ints.
> If you set the ints up so that an int is generated on the rising edge of
> portb0 and increment a counter every time an int is generated you can
> count pulses. now if you also set the clock to generate an int at a set
> duty cycle you can count the number of pulses on the portb0 pin within a
> set time. all of this can be done in the background and due to the
> nature of the ints it is also VERY presise.
>
> I hope this is of some use
>
> Peter........
I think the problem is that the output of serial data will be
corrupted by the interrupts.
Peter.
--
_______________________________________________________________________
Peter Homann email: EraseMEpeterhspamBeGoneKILLspamadacel.com.au Work : +61 3 9596-2991
Adacel Pty Ltd Fax : +61 3 9596-2960
250 Bay St, Brighton 3186, VIC, AUSTRALIA Mobile : 014 025-925
Robert Lunn wrote:
>
> >I need to measure a continuous frequency between 0 - 250 cycles/MINUTE,
> >and transmit it via RS-232 at 2400 baud in a message containing 6 bytes
> >once 5 seconds.
> >
> >The PIC I plan to use is the low power 84 variant, running at 32 KHz,
> >if possible.
>
> Peter, you don't indicate the accuracy with which you need
> to measure the frequency...
Bob,
I only need an accuracy of +/- 0.5 cycles/minute.
Peter
--
_______________________________________________________________________
Peter Homann email: RemoveMEpeterhspamBeGonespamadacel.com.au Work : +61 3 9596-2991
Adacel Pty Ltd Fax : +61 3 9596-2960
250 Bay St, Brighton 3186, VIC, AUSTRALIA Mobile : 014 025-925
Robert Lunn wrote:
>
> >I need to measure a continuous frequency between 0 - 250 cycles/MINUTE,
> >and transmit it via RS-232 at 2400 baud in a message containing 6 bytes
> >once 5 seconds.
> >
> >The PIC I plan to use is the low power 84 variant, running at 32 KHz,
> >if possible.
>
> Peter, you don't indicate the accuracy with which you need
> to measure the frequency...
>
> However, with a 32.768 kHz clock (which is 8192 instructions
> per second) a variation of one instruction in detecting the
> edge of a 250 rpm signal will cause an error in the calculated
> instantaneous frequency of 0.2 rpm.
>
> Assuming you don't want your measurement to be much less
> accurate than this, you must measure the edges of the input
> signal to within an instruction time.
>
> You can do this by setting up TMR0 as a free running timer
> with no prescale, configuring RB0 as an interrupt, and
> connecting your input signal to RB0.
>
> On each rising edge you get an interrupt, and in your ISR
> you capture TMR0.
>
> You must handle overflow of TMR0 in your main line code.
>
> You are now measuring your signal period, and thus your
> signal frequency, as accurately as it is possible.
Seems a good solution so far.
>
> Ok, now to the output side of the equation...
>
> I can solve your problem if I can change your requirements :-)
>
> Use 300 baud instead of 2400 baud (which is barely possible
> anyway).
300 baud may be a bit slow, Ill have to check. 1200baud is preferred.
I want to use a 32KHz crystal because of its availability. Maybe I'll
have to use a faster one, so as to increase the baud rate. The reason
for the slow crystal is purely for power consumption reasons.
>
> At 300 baud you have just over 27 instructions per bit. The
> ISR to capture TMR0 should be six instructions. This interrupt
> can never occur more than once per character (indeed, can never
> occur more than once per six byte transmission). Stretching
> a single bit time by 20% will _probably_ be ok...
>
> Don't forget to handle TMR0 overflow between each byte.
>
> ___Bob
Thanks again,
Peter.
--
_______________________________________________________________________
Peter Homann email: @spam@peterhspamadacel.com.au Work : +61 3 9596-2991
Adacel Pty Ltd Fax : +61 3 9596-2960
250 Bay St, Brighton 3186, VIC, AUSTRALIA Mobile : 014 025-925
> I need to measure a continuous frequency between 0 - 250 cycles/MINUTE,
> and transmit it via RS-232 at 2400 baud in a message containing 6 bytes
> once 5 seconds.
>
> The PIC I plan to use is the low power 84 variant, running at 32 KHz,
> if possible.
I'd suggest doing the following:
[1] Use the following variables:
CurrTime : 16-bit
LastEvent : 16-bit
LastEvLatch : 16-bit
PrevEvent : 16-bit
NextOutput : 16-bit
At 09:02 07/11/96 +1100, Peter Homann wrote:
>I think the problem is that the output of serial data will be
>corrupted by the interrupts.
Didn't you say that you need to send only in quite big intervals? How about
stopping measuring while sending data, if there really is a timing problem?
Gerhard Fiedler wrote:
>
> At 09:02 07/11/96 +1100, Peter Homann wrote:
> >I think the problem is that the output of serial data will be
> >corrupted by the interrupts.
>
> Didn't you say that you need to send only in quite big intervals? How about
> stopping measuring while sending data, if there really is a timing problem?
Although I wish to initially transmit approximately once every
five seconds, eventually I would like to speed it up. Otherwise I
could restart the measurement after the transmission has finished.
At 20 rpm the period is 3S. The worst case is when the pulse is
missed during transmission and the next pulse is not for another
3 seconds, then the next pulse is another 3 seconds a delay of
6 seconds before the frequency value is calculated.
If necessary I can live with this but its not ideal.
I plan to transmit the signal at a random interval, averaged at
once every 5 seconds. It would be nice to have the "Current"
value ready for when the transmission is required.
The reason for the random transmission is that there is more than one
unit transmitting. A poor mans ethernet with no collision detection
by the sender. If the receiver get a screwed message it ignores it
and picks up the value on the next transmission.
--
_______________________________________________________________________
Peter Homann email: TakeThisOuTpeterhKILLspam@spam@adacel.com.au Work : +61 3 9596-2991
Adacel Pty Ltd Fax : +61 3 9596-2960
250 Bay St, Brighton 3186, VIC, AUSTRALIA Mobile : 014 025-925
> Although I wish to initially transmit approximately once every
> five seconds, eventually I would like to speed it up. Otherwise I
> could restart the measurement after the transmission has finished.
>
> I plan to transmit the signal at a random interval, averaged at
> once every 5 seconds. It would be nice to have the "Current"
> value ready for when the transmission is required.
>
> The reason for the random transmission is that there is more than one
> unit transmitting. A poor mans ethernet with no collision detection
> by the sender. If the receiver get a screwed message it ignores it
> and picks up the value on the next transmission.
What would happen if you were to, after each input pulse, randomly decide
to output a packet [possibly with some random delay beforehand]? If you
have observed the input frequency as 60bpm, you could wait up to about 800ms
after an input transition before sending your packet and still be done
in time for the next input; if your frequency is faster (e.g. 240bpm) you
can't wait as long but you have a better selection of pulses to trigger
on.
I decided that I had better do a bit of investigation in my
problem. Below are some thoughts and a possible solution. All
comments are welcome. Be kind as this is my first cut at it.
Therefore I need to calculate the frequency over
different number of Signal pulses depending on the frequency.
When the count gets greater then a particular value
the frequency is then calculated.
--------------------------------------------------------
Therefore use 1.953ms (32768/512) for timer increment so;
@ 250rpm period is 60/250 = 240.00mS and @ 1.9531ms = 122.88 counts
@ 249rpm period is 60/249 = 240.96mS and @ 1.9531ms = 123.37 counts
At this rate we would need to count over at least 2 cycles.
At the minumum frequency.
@ 20rpm period is 60/20 = 3.000S and = 1536 counts
@ 21rpm period is 60/21 = 2.857S and = 1642 counts
At this rate we could count over a single cycle.
Therefore we should be looking for about 300 counts.
Use of Interrupts
-----------------
Because the PIC is beign run of a 32KHz crystal, the CPU will not
need to utilise sleep modes as the current consumption is approx
65uA, therefore interrupts may not be needed as;
o The bit banging can't be interrupted
o If its time to send a message and we're calculating the
signal frequency or something else, we can wait until we're
finished. It doesn't matter that we're 1/2 sec late.
o At 32KHz there are onky 8K instructions/sec. Overheads in
processing the interrupts may be significant
o Use the KISS principle whereever possible.
Message Transmission
--------------------
For 5 bytes, ie 50 bits (1 Start, 1 Stop, 8 Data)
At 1200 baud 50 / 1200 = 42ms
At 1200 baud 1 byte takes approx 5ms
If we don't get a Signal during the transmission then everything is
fine. If we do, we can't detect it until the byte is banged out as
there is not enough time during the transmission to check it.
Note: we may even be able to wait until the whole message has
been sent. If the signal stays low for longer than 50ms we may
be able to guarantee it will still be low after the message is sent.
We could also use a flip-flop on the signal and then check
transitions in either direction. But this is more hardware and thus
more power and board real-estate.
Frequency Measurement
---------------------
To measure the frequency between 20 - 250 rpm the timer could
set up so as to overflow every 500ms. Whenever the Signal is detected,
the timer value is recorded. The period of the frequency is the
absolute difference between the timer value for a number of pulses. If
the absolute value is too small to get an accurate frequency
calculation, we can just wait for the next pulse, using the
totalled period duration.
We can also "defer" the frequency calculation if we are busy doing
other things, ie bit banging out the serial message.
The PIC 16C84 has an 8 bit timer(I think) with a prescaler.
Therefore, if we overflow at 0.5 second, we get a resolution of
just under 2 ms (1.9531ms).
Example
-------------
If we use 1.9531ms timer increments we get
512 counts /sec
or
30720 counts/minute
Using a bit of scaled arithmetic;
freq = 1/Period
Freq = 30720/count
for more accuracy use 30720 * 2 = 61440
Therefore the frequency is
F = ((61440 / count ) * number_of_Signals) / 2)
Example:
for a frequency of say 220 rpm over 3 pulses.
Period for 3 pulses is .818s
Count = 0.818/.001953 = 418
Freq = ((61440/418) * 3 ) / 2
= 219 rpm
BEGIN Main
. CALL Reset_Signal_Timing
. WHILE forever
. . CALL Check_Signal
. . CALL Check_Timer_Overflow
. . CALL Check_Transmission
. ENDWHILE
END Main
BEGIN Reset_Signal_Timing
. Set the present_count to 0
. Set the last_time_count to 0
. Set the number_of_Signals to 0
. Set the overflow_count to 0
. Set Timing_In_Progress to FALSE
END Reset_Signal_Timing
BEGIN Check_Signal
. IF Signal line has Hi to Lo transition
. . Set the present_count to the current counter value
. . Increment the number_of_Signals received
. . Set Timing_In_Progress to TRUE
. . CALL Calculate_Frequency
. ENDIF
END Check_Signal
BEGIN Calculate_Frequency
. Calculate the absolute interval
. IF the interval > MIN_PERIOD
. . IF the interval < MAX_PERIOD
. . . Calculate Temp = ???? / interval
. . . Calculate Frequency = Temp/Number_of_Signals
. . . Set the number_of_Signals received to zero
. . . Set the last_time_count to the present_count value
. . . Set the overflow_count to 0
. . ELSE
. . . CALL Reset_Signal_Timing
. . ENDIF
. ENDIF
END Calculate_Frequency
BEGIN Check_Timer_Overflow
. IF the timer has over flowed
. . IF overflow_count > MAX_OVERFLOW_COUNT
. . . CALL Reset_Signal_Timing
. . ELSE
. . . Increment the overflow_count
. . END
. END
END Check_Timer_Overflow
BEGIN Check_Transmission
. IF it is time to transmit
. . FOR x = 1 to 5
. . . Bit bang out byte(x)
. . . IF Signal line has Hi to Lo transition
. . . . Increment number_of_Signals received
. . . ENDIF
. . ENDFOR
. . IF the counter has overflowed
. . . Increment overflow_count
. . ENDIF
. . Calculate the next transmission time
. ENDIF
END Check_Transmission
--
_______________________________________________________________________
Peter Homann email: .....peterhRemoveMEadacel.com.au Work : +61 3 9596-2991
Adacel Pty Ltd Fax : +61 3 9596-2960
250 Bay St, Brighton 3186, VIC, AUSTRALIA Mobile : 014 025-925
>
> > Although I wish to initially transmit approximately once every
> > five seconds, eventually I would like to speed it up. Otherwise I
> > could restart the measurement after the transmission has finished.
> >
> > I plan to transmit the signal at a random interval, averaged at
> > once every 5 seconds. It would be nice to have the "Current"
> > value ready for when the transmission is required.
> >
> > The reason for the random transmission is that there is more than one
> > unit transmitting. A poor mans ethernet with no collision detection
> > by the sender. If the receiver get a screwed message it ignores it
> > and picks up the value on the next transmission.
>
> What would happen if you were to, after each input pulse, randomly decide
> to output a packet [possibly with some random delay beforehand]? If you
> have observed the input frequency as 60bpm, you could wait up to about 800ms
> after an input transition before sending your packet and still be done
> in time for the next input; if your frequency is faster (e.g. 240bpm) you
> can't wait as long but you have a better selection of pulses to trigger
> on.
John,
Yes it is possible. I'm not sure that a pattern may develop because
the randomised interval may be less. I'll need to think about it. My
original concept was to have the current frequency alway available,
and the transmission part would just use that latest value when it
needed to transmit the message.
Thanks for your input. I look forward to tomorrows replys. I'm off
now and will think about the problem further.
Thanks again.
Peter.
--
_______________________________________________________________________
Peter Homann email: KILLspampeterhTakeThisOuTadacel.com.au Work : +61 3 9596-2991
Adacel Pty Ltd Fax : +61 3 9596-2960
250 Bay St, Brighton 3186, VIC, AUSTRALIA Mobile : 014 025-925
>Robert Lunn wrote:
>>
>> >I need to measure a continuous frequency between 0 - 250 cycles/MINUTE,
>> >and transmit it via RS-232 at 2400 baud in a message containing 6 bytes
>> >once 5 seconds.
>>
>> Peter, what's the six-byte message you send?
>>
>> (I want to get a handle on the processing required to
>> create the message string.)
>
>Bob,
>
>Sorry, but there are only five bytes and are as follows;
>
>Byte Description
>-----------------------------------------------------------------
> 1 Start of Message ID Constant
> 2-3 Unit Identification 15 bits constant (1 bit battery low)
> 4 Frequency Value Variable
> 5 Checksum Variable
>
>Sorry for the delay in answering, and thanks for your interest.
>
>Regards,
>
>Peter
Hmm. A six byte message at 1200 baud takes 0.05 seconds. At 250 rpm the
input pulses arrive every 0.3 seconds. So there's enough time between pulses
to send multiple messages if necessary.
Providing your transmit routine waits until just after a pulse (or counter
overflow when there's no input) it should have hardly any problems with
packets corrupted by interrupt servicing routines, in fact you should
probably disable the interrupt for 100mS after each pulse.
Disabling the interrupt allows for the situation where the flag is
stationary on the edges of the sensor and produces anomolously high
readings. These noise readings appear as 600 rpm and can be filtered out
(binned).
Just a few thoughts,
Keith.
==========================================================
Keith Dowsett "Variables won't; constants aren't."
>Gerhard Fiedler wrote:
>> Didn't you say that you need to send only in quite big intervals? How about
>> stopping measuring while sending data, if there really is a timing problem?
>
>Although I wish to initially transmit approximately once every
>five seconds, eventually I would like to speed it up. Otherwise I
>could restart the measurement after the transmission has finished.
>
As others have mentioned, it seems that the best solution is to send the
data immediately after receiving an input pulse. It has already been
demonstrated that if you use this technique under the operating conditions
you have described, you will not miss and input pulses.
I don't know how long the 'data conversion' steps take, but it is likely
you could wait for an input pulse, do your calculations, and send the data
before another input pulse arrives.
Or am I missing something? Also, you're guaranteed to have one measurement
at least every three seconds, according to your operating conditions.
-Matt
"DOS Computers manufactured by companies such as IBM, Compaq, Tandy, and
millions of others are by far the most popular, with about 70 million
machines in use wordwide. Macintosh fans, on the other hand, may note that
cockroaches are far more numerous than humans, and that numbers alone do
not denote a higher life form."
I have a project which needs a battery powered real-time clock (RTC) chip. The
chip should have a serial port that can be connected to a PIC16C54. Does any
one know where there is such kind of chip, its type and source? Any help is
greatly appriciated.
Zemin Liu wrote:
>
> HI,
>
> I have a project which needs a battery powered real-time clock (RTC) chip. The
> chip should have a serial port that can be connected to a PIC16C54. Does any
> one know where there is such kind of chip, its type and source? Any help is
> greatly appriciated.
>
> Z. Liu
Zemin,
I suggest you have a look at the Dallas DS1302. This is an 8-pin
animal, it has very low current requirements, and is relatively easy to
talk to using a '54.
For further information on the device, check out their web site at
http//http://www.dalsemi.com/.
Zemin Liu wrote:
> I have a project which needs a battery powered real-time clock (RTC) chip. The
> chip should have a serial port that can be connected to a PIC16C54. Does any
> one know where there is such kind of chip, its type and source? Any help is
> greatly appriciated.
SimmStick(tm) A PIC proto PCB the size of a 30 pin Simm Memory Module.
EASY PIC'n Beginners Guide to using PIC 16/17 MicroChip products.
MEL PicBasic Compiler. Programmers from 15 USD. Pic-Axe(tm) A New Tool.
Don McKenzie wrote:
>
> Zemin Liu wrote:
> > I have a project which needs a battery powered real-time clock (RTC) chip.
The
> > chip should have a serial port that can be connected to a PIC16C54. Does
any {Quote hidden}
> > one know where there is such kind of chip, its type and source? Any help is
> > greatly appriciated.
>
> http://www.labyrinth.net.au/~donmck/rtc.html
> has pointers to PIC code examples and data sheets on the Panasonic
> NJU6355 and Dallas 1202/1302 Real Time Clocks.
>
> Don McKenzie .....donmckEraseMElabyrinth.net.au
> DonTronics Tullamarine, Australia
> http://www.labyrinth.net.au/~donmck
>
> SimmStick(tm) A PIC proto PCB the size of a 30 pin Simm Memory Module.
> EASY PIC'n Beginners Guide to using PIC 16/17 MicroChip products.
> MEL PicBasic Compiler. Programmers from 15 USD. Pic-Axe(tm) A New Tool.
Try Philips 8583. It's a IIC device. Works well.
--
Friendly Regards
Tjaart van der Walt
______________________________________________________________
| Another sun-deprived R&D Engineer slaving away in a dungeon |
|WASP International GSM vehicle tracking and datacomm solutions|
| +27-(0)11-622-8686 | http://wasp.co.za |
|______________________________________________________________|
> I have a project which needs a battery powered real-time clock (RTC) chip. The
> chip should have a serial port that can be connected to a PIC16C54. Does any
> one know where there is such kind of chip, its type and source? Any help is
> greatly appriciated.
I'm currently developing a genlocked time display for video camera signals,
the clock chip I'm using is the Philips PCF8583P. This is an eight pin I2C
chip, and also includes 256 bytes of EEPROM which can be used for storage.
I've not got it hooked up to a PIC yet, but I've got it connected to my PC,
and with the power disconnected it consumes 2.4uA from a 2.4v nicad.
In the UK it's available from RS Components, or many other sources. It's also
used in a number of VCR's, in particular Grundig ones (with a battery, so the
clock is always running), and in a Sharp TV/VCR (with a capacitor, only gives
a limited backup).
Nigel.
/--------------------------------------------------------------\
| Nigel Goodwin | Internet : spamnigelgspam_OUT@spam@lpilsley.demon.co.uk |
| Lower Pilsley | Web Page : http://www.lpilsley.demon.co.uk |
| Chesterfield | |
| England | |
\--------------------------------------------------------------/
At 07:34 PM 11/17/96 +0800, you wrote:
>HI,
>
>I have a project which needs a battery powered real-time clock (RTC) chip. The
> chip should have a serial port that can be connected to a PIC16C54. Does any
> one know where there is such kind of chip, its type and source? Any help is
> greatly appriciated.
>
>Z. Liu
>
Dallas Semi makes ALL KINDS of realt time clocks, with various features and
whatsits. Many can be battery backed for 10 years with a lithium battery
(uh... I think... this is from memory). Call Dallas and get a databook.
>>
>>I have a project which needs a battery powered real-time clock (RTC) chip. The
>> chip should have a serial port that can be connected to a PIC16C54. Does any
>> one know where there is such kind of chip, its type and source? Any help is
>> greatly appriciated.
>>
>>Z. Liu
>
Phillips semiconductor makes a low power clock/calendar chip with an I2C
interface, I;ve used this chip with great success backed-up with a lithium
battery. Ask for Phillips' I2C data book/catalog.
I also have the need to keep a clock running using a minimum of battery
current, and I was planning to go mostly software for the clock, instead of
a dedicated chip.
my plan is
1>install a 32.768 KHz xtal to T1osc pins. I am looking to the 16C74 but
other chips have same capability.
2>control the clock increments with a Timer one interrupt routine.
3>put the pic to sleep during the time was not processing data.
During this period the 32KHZ oscillator will remain working, providing an
interrupt and wake up of the PIC, every desired period of time , up to two
seconds, ( see microchip AN580).
the interrupt routine will be something like;
int mili_sec,sec,min,hour,day,month,clock_flag;
#INT_TIMER1
TIMER1_INT_HANDLER()
{
Timer_1_high = 0x80; // one second interrupt periods
// this will be the adjustment to compensate
// for slow / fast xtals
if (++sec>=60)
{
sec =0;
if (++min>=60)
{
min = 0;
if (++hour>=24)
{
hour = 0;
++day;
IF ((day>28)&&(month==2)) // requires more work for leap year
day = 32;
IF((day>30)&&(((month<8)&&(!BIT_TEST(month,0)))
||((month>7)&&(BIT_TEST(month,0)))) )
day = 32;
IF ( day >31)
{
day = 1;
if (++month>12)
month = 1; // year update not included yet
}
}
}
}
{
clock_flag = true; // clock_flag true will advise
// main routine to display clock
// , clear flag and set pic to sleep.
}
}
appears to me that having the code space this approach should be cheaper
than a dedicated chip.
juan
>X-Sender: spammmucker@spam@STOPspammail.airmail.net
>Date: Mon, 18 Nov 1996 12:28:40 -0600
>Reply-To: pic microcontroller discussion list <spamBeGonePICLISTspamBeGone@spam@MITVMA.MIT.EDU>
>Sender: pic microcontroller discussion list <RemoveMEPICLISTRemoveMERemoveMEMITVMA.MIT.EDU>
>From: Matthew Mucker <mmuckerKILLspamspamAIRMAIL.NET>
>Subject: Re: Low power RTC chip with serial interface
>To: Multiple recipients of list PICLIST <spam_OUTPICLIST@spam@MITVMA.MIT.EDU>
>
>At 07:34 PM 11/17/96 +0800, you wrote:
>>HI,
>>
>>I have a project which needs a battery powered real-time clock (RTC) chip. The
>> chip should have a serial port that can be connected to a PIC16C54. Does any
>> one know where there is such kind of chip, its type and source? Any help is
>> greatly appriciated.
>>
>>Z. Liu
>>
>Dallas Semi makes ALL KINDS of realt time clocks, with various features and
>whatsits. Many can be battery backed for 10 years with a lithium battery
>(uh... I think... this is from memory). Call Dallas and get a databook.
>
>-Matt
>
>
Hey, gang. I'm not sure where this thread has lead since I'm still a
week or so behind on my digests, but...
The 16F84-04/P through DigiKey is $6.48 in singles and $4.31 in 100s,
while the 16C62A-04/SP is $5.35 in singles and $3.56 in 100s. This
indicates that the '62A is cheaper than the '84 (your mileage may
vary), even though the former is in a skinney 28 rather than the 18
pin pkg.
This is significant in that the '62A HAS one CCP module that you can
capture the input waveform with WHILE you are bit-banging out the
other end. You can use TMR0 for the baud-rate generator to interrupt
you at the next bit time, and the CCP will interrupt you after the
capture has occured.
Checking two interrupt sources should not give too much of an
erroneous bit time at 1200/2400 baud, and leaving TMR2 can be used for
baud-rate generation using the period register for continuous
constant-period bit-time interrupts.
However, if you HAVE an '84 and you're just trying to use IT, then
that is another story. If you're trying to do the most efficient job,
though, I'd recommend the '62A.
> my plan is
> 1>install a 32.768 KHz xtal to T1osc pins. I am looking to the 16C74 but
> other chips have same capability.
> 2>control the clock increments with a Timer one interrupt routine.
> 3>put the pic to sleep during the time was not processing data.
> During this period the 32KHZ oscillator will remain working, providing an
> interrupt and wake up of the PIC, every desired period of time , up to two
> seconds, ( see microchip AN580).
>
> appears to me that having the code space this approach should be cheaper
> than a dedicated chip.
This approach has many advantages; among them: the potential ability to
use a cheap RC oscillator as your main CPU clock. For applications that
will be periodically waking from sleep, an RC clock can be extremely des-
irable because unlike a crystal it can start up nearly instantly.
Unfortunately, according to Microchip's errata sheet for the 16C74, that
oscillator really isn't as useful as you'd like. If memory serves...
[1] When the main oscillator is running, it can sometimes garble the
oscillation of T1.
[2] When T1 is running, the part uses an excessive amount of power (which
pretty much defeats the purpose of sleep mode).
If Microchip produced a chip which fixed these problems, added a gray-counter
to the UART (allowing much finer baud-rate control and rendering the BRGH
bug irrelevant), included a built-in programmable/nudgeable RC, and was nice
and cheap... well, I'd sure like 'em.
By gray counter, btw, I mean a counter which uses graycode step patterns in
a feedback circuit to allow fractional counting. For not much more logic
than a self-reloading timer, you could have a counter which would output
2^K [K=0..6] pulses for every 256-N [N=0..127] put in. Such a timer could
generate any baud rate within its range, within 1%; if its range needed to
be extended, a simple prescalar would suffice. Given the combination of
such a baud-rate generator, a 32KHz crystal, and an RC oscillator, it would
be practical to have a device sleep while waiting for serial input and be
able to grab the first byte. Would anyone else find such a device interest-
ing?
I want to develop my own Programmer (Everybody else is doing it), but I want
to do a couple of things differently.
A big one is, I want to use a AC/DC Wall Adapter (aka "Wall Wart") for power
and another PIC (probably a 16C54) to control and communicate with the host
PC. Now to simplify it, I want to use the incoming DC (15V) as the Vpp
reference.
Now, when I started looking at controlling the Vpp, I wondered about the
following circuit for Vpp:
+12V ---------+
|
<
> 10K Current Limiting
< Resistor
>
| 1401
PIC Output ----+-------------|>|-------- To Programmed Part _MCLR
For Programming, the PIC Output Bit would be set to Input Mode (the
corresponding TRIS Bit = 1). Otherwise (ie when the PIC is being pulled out
of the socket), TRIS=Bit=0 to drop the line down low and isolated it using
the diode.
I don't think there will be any problems. According to the Programming
Spec, a max of 200 uAmps is drawn through the _MCLR Bit (which would cause a
2 Volt Drop across the 10K Resistor) and there is a 0.7Volt drop through the
1401 diode. When the PIC pulls the Line down, there will only be 1.5 mAmp
being sunk.
If I start with 15 Volts, I will loose a max of 2 Volts through the 10K
resistor and 0.7 Volts thru the diode. This leaves 12.3 Volts for
programming (enough to trip the PIC into programming mode).
Does anybody see any problems with this/reasons why I wouldn't want to
program a PIC using this method?
myke
Today, the commercial sector is advancing computer and communication
technology at a breakneck pace. In 1992, optical fiber was being installed
within the continental U.S. at rates approaching the speed of sound (if
computed as total miles of fiber divided by the number of seconds in the year).
Aviation Week and Space Technology, October 28, 1996
>For Programming, the PIC Output Bit would be set to Input Mode (the
>corresponding TRIS Bit = 1). Otherwise (ie when the PIC is being pulled out
>of the socket), TRIS=Bit=0 to drop the line down low and isolated it using
>the diode.
This will only work for the 16C84. All other parts will need a _real_
13V, 50 mA typical source.
>I don't think there will be any problems. According to the Programming
>Spec, a max of 200 uAmps is drawn through the _MCLR Bit (which would cause a
>2 Volt Drop across the 10K Resistor) and there is a 0.7Volt drop through the
>1401 diode. When the PIC pulls the Line down, there will only be 1.5 mAmp
>being sunk.
The voltage tolerance is rather tight. Two volts of slop based on the
_assumption_ that 200 uA will be drawn may end up applying 15V to ~MCLR,
killing your chip.
>Does anybody see any problems with this/reasons why I wouldn't want to
>program a PIC using this method?
> Now, when I started looking at controlling the Vpp, I wondered about the
> following circuit for Vpp:
>
>
> +12V ---------+
> |
> <
> > 10K Current Limiting
> < Resistor
> >
> | 1401
> PIC Output ----+-------------|>|-------- To Programmed Part _MCLR
>
>
> For Programming, the PIC Output Bit would be set to Input Mode (the
You're assuming the contorlling PIC is essentially disconnected when the
pin is set to iput, but most (?) of the PIC chips have diodes to ground
and Vc, so this won't work. Even if you use RA4, which lacks the diode to
Vc, you may or may not get satisfactory results, as the PIC still isn't
rated for operation much above the supply. So maybe it will work for a
while and then the controlling PIC will flake out - who knows?
Another problem is that Microchip specifies a rather fast risetime for Vpp
when entering programming mode - without checking I might guess it was 1
or 2 microseconds. With 100K series R you don't need much stray
capacitance to slow down that rising edge to the point of causing
problems, perhaps annoying intermittent ones.
And then, as has been mentioned already, most PICs are spec'd for a much
larger current draw during programming, so this could only work for the
16C84 if it works at all.
> If I start with 15 Volts, I will loose a max of 2 Volts through the 10K
> resistor and 0.7 Volts thru the diode. This leaves 12.3 Volts for
> programming (enough to trip the PIC into programming mode).
Even if that 15 volts is regulated this is pretty marginal, though again
it may well work most fo the time. If the 15V is unregulated, then it
won't be 15V most fo the time (but it may still work sometimes - PICs,
like most modern electronics, are capable of performance well beyond the
spec'd limits, at least some of them, at least some of the time).
> Does anybody see any problems with this/reasons why I wouldn't want to
> program a PIC using this method?
>Hi Folks,
>
>I want to develop my own Programmer (Everybody else is doing it), but I want
>to do a couple of things differently.
>
>A big one is, I want to use a AC/DC Wall Adapter (aka "Wall Wart") for power
>and another PIC (probably a 16C54) to control and communicate with the host
>PC. Now to simplify it, I want to use the incoming DC (15V) as the Vpp
>reference.
>
>Now, when I started looking at controlling the Vpp, I wondered about the
>following circuit for Vpp:
>
>
> +12V ---------+
> |
> <
> > 10K Current Limiting
> < Resistor
> >
> | 1401
> PIC Output ----+-------------|>|-------- To Programmed Part _MCLR
>
>
>For Programming, the PIC Output Bit would be set to Input Mode (the
>corresponding TRIS Bit = 1). Otherwise (ie when the PIC is being pulled out
>of the socket), TRIS=Bit=0 to drop the line down low and isolated it using
>the diode.
>
>I don't think there will be any problems. According to the Programming
>Spec, a max of 200 uAmps is drawn through the _MCLR Bit (which would cause a
>2 Volt Drop across the 10K Resistor) and there is a 0.7Volt drop through the
>1401 diode. When the PIC pulls the Line down, there will only be 1.5 mAmp
>being sunk.
>
>If I start with 15 Volts, I will loose a max of 2 Volts through the 10K
>resistor and 0.7 Volts thru the diode. This leaves 12.3 Volts for
>programming (enough to trip the PIC into programming mode).
>
>
>Does anybody see any problems with this/reasons why I wouldn't want to
>program a PIC using this method?
>
>myke
Hi Myke,
first reason: C54 does not have open colletor outputs, what means that
all IO pins _do_ have input protection diodes to VSS _and_ VCC ie maximum
voltage on any IO pin (being tri-stated) will not exceed VCC+.7 ie ~5.7V
and thats not enough to enter into programming mode.
I am not sure if RA4 on 16CXX devices can be used, well it can but it
may not be to the specs on maximum allowed voltage on io pin
myke predko wrote:
>
> Hi Folks,
>
> I want to develop my own Programmer (Everybody else is doing it), but I want
> to do a couple of things differently.
>
BIG Snip
Myke.
Why not use an opto isolator to drive the Vpp pin the source current
of the driving diode is quite small and the speed of switching is more
than fast enough. It's what I used. As for the programming voltahe I
used a LM7812 regulator and placed a Diode in series with the Vref to
ground. this has the effect of raising the OP voltage to about 13.5
volt.
you can use the same trick for the 5 volt rail and a couple of
buffers/inverters for the programming lines.
So there you have it 2 voltage regs,2 optos and one 7404. Your
programmer is complete.
Cheers Peter......
==================================
= New Ideas come from those who =
= didn't know it wasn't possible =
==================================
Thanx for all the replies. Oh well, it seemed like a good idea at the time
(is there a sheepish grin character?).
Peter,
I think I would go with your suggestion. I presume the circuit would be:
______
+15V-----+----------| 7812 |-----+--------------------+ +--- To Pwr
| |______| | | | Control
---Filter | ---Filter \| -
---Cap - ---Cat | ^
| ^Diode | /| |
| | | | |
+--------------+--------+ | +--- To +5V
| To PIC
Gnd to be
Programmed
For the Programming Voltage?
Also, thanx for the suggestion about doing +5V as well (I forgot about
that). I already have a 7805 in the Circuit, so adding this won't be a
problem. (Just an opto-isolator in this case.)
Just out of curiosity,
Again, thanx to Antti, Martin, and Hank for pointing out that my circuit
wouldn't work for 16C61s, and 16C71s (which is really what I wanted it for
rather than just the 16C84).
>>
>> Hi Folks,
>>
>> I want to develop my own Programmer (Everybody else is doing it), but I want
>> to do a couple of things differently.
>>
>BIG Snip
>
>Myke.
> Why not use an opto isolator to drive the Vpp pin the source current
>of the driving diode is quite small and the speed of switching is more
>than fast enough. It's what I used. As for the programming voltahe I
>used a LM7812 regulator and placed a Diode in series with the Vref to
>ground. this has the effect of raising the OP voltage to about 13.5
>volt.
>
> you can use the same trick for the 5 volt rail and a couple of
>buffers/inverters for the programming lines.
>
> So there you have it 2 voltage regs,2 optos and one 7404. Your
>programmer is complete.
>
>
>Cheers Peter......
>
>==================================
>= New Ideas come from those who =
>= didn't know it wasn't possible =
>==================================
>
>
Today, the commercial sector is advancing computer and communication
technology at a breakneck pace. In 1992, optical fiber was being installed
within the continental U.S. at rates approaching the speed of sound (if
computed as total miles of fiber divided by the number of seconds in the year).
Aviation Week and Space Technology, October 28, 1996
>Thanx for all the replies. Oh well, it seemed like a good idea at the time
>(is there a sheepish grin character?).
>
>Peter,
>
>I think I would go with your suggestion. I presume the circuit would be:
>
> ______
> +15V-----+----------| 7812 |-----+--------------------+ +--- To Pwr
> | |______| | | | Control
> ---Filter | ---Filter \| -
> ---Cap - ---Cat | ^
> | ^Diode | /| |
> | | | | |
> +--------------+--------+ | +--- To +5V
> | To PIC
> Gnd to be
> Programmed
>
>For the Programming Voltage?
>
>Also, thanx for the suggestion about doing +5V as well (I forgot about
>that). I already have a 7805 in the Circuit, so adding this won't be a
>problem. (Just an opto-isolator in this case.)
>
Mike,
You need at least one more diode in the common pin of the 7812. I use two but
I noticed Robin Abbott goes with Three. Either will put you in range but just
one diode is a little low.
I think using an opto coupler is a little extravagant. You certainly don't
need
one for the 5v Vdd, just use any GP PNP transistor and a single resister in
the
base line. (High = off and low = on.)
For the 13V Vpp, you need to do some level shifting. An opto coupler
can do that but I think a PNP transistor switched by a common emitter NPN
transistor is a cheaper alternative. You will need 3 resisters, 2 in each base
line and one on the collector-base junction of the PNP "series pass" switch.
You can also use two NPN transistors and a zener diode reference. configure
the first NPN as a common collector with 14V worth of zener/led/diode drop
on the base
and a pullup to unreg 16V. This will give 13.4 volts out on the emitter. To
turn it off, the second (common emitter) NPN is biased on and its collector
pulls the base
of Q1 to ground thus turning Vpp off.
This is how the parallax programmer does it. You will also see the same
arrangement
shortly when the postman comes. Feel free to copy me because I copied it from
parallax already. :-)
Sorry I have not done any diagrams but at 1:45AM and, for nothing, forget
it! :-)
PHOENIX Shareware Picstart 16B upgrade coming.
For more details, send email to KILLspamnewfound.....TakeThisOuTne.com.au with
"subscribe phoenix mail list" in the BODY of the message.
--------------------------------------------------------
>
> Thanx for all the replies. Oh well, it seemed like a good idea at the time
> (is there a sheepish grin character?).
>
> Peter,
>
> I think I would go with your suggestion. I presume the circuit would be:
>
> ______
> +15V-----+----------| 7812 |-----+--------------------+ +--- To Pwr
> | |______| | | | Control
> ---Filter | ---Filter \| -
> ---Cap - ---Cat | ^
> | ^Diode | /| |
> | | | | |
> +--------------+--------+ | +--- To +5V
> | To PIC
> Gnd to be
> Programmed
>
That looks like it but might i suggest a pull down on the open end of
the opto to pull it back to GND when it is not switched on. It will just
float otherwise and not return to GND. I used a value of 10K for mine.
Peter ........
==================================
= New Ideas come from those who =
= didn't know it wasn't possible =
==================================
Myke, take a look at the web site below. Steve has a nifty PIC
programmer that runs from a PC parallel port. Doesn't use any PICs to
run it. He has a PC program to do the programming, of course.
I built it, and it works like a charm. Even if you build your won, you
could use Steve's ideas for driving the PIC lines. Basically, he uses a
couple of transistors driven by CMOS logic chips at 5 volts ... same as
the PIC.
>----------
>From: myke predko[SMTP:TakeThisOuTmykeEraseMERemoveMEPASSPORT.CA]
>Sent: Sunday, November 24, 1996 2:43 PM
>To: Multiple recipients of list PICLIST
>Subject: Programmer Power
>
>Hi Folks,
>
>I want to develop my own Programmer (Everybody else is doing it), but I want
>to do a couple of things differently.
>
>(snip)
>
>I want to develop my own Programmer (Everybody else is doing it), but I want
>to do a couple of things differently.
>
>A big one is, I want to use a AC/DC Wall Adapter (aka "Wall Wart") for power
>and another PIC (probably a 16C54) to control and communicate with the host
>PC. Now to simplify it, I want to use the incoming DC (15V) as the Vpp
>reference.
I am using an AN589 based PIC programmer, but add some futures:
* An extra LED indicating 13,5V on the output can be VERY helpful for
troubleshooting
* I use a switching step-up converter 5V -> 13,5V. I got this Idea from
a German HAM-radio magazine. So I can use a AC/AC Wall Adapter with
7 - 20 V AC output to power the programmer and the PIC circuit or I
can
use the +5V from my PIC circuit to power the programmer. Since most of
my projects have their own power supply, it makes programming easy.
I am using this programmer for 'in-circuit' programming.
After a while, I discovered this problems:
What happens on the programmers outputs, if :
* The programmer is powered, but not connected to the PC
* The programmer is powered and connected to the PC, which is off
* The programmer is powered and connected to a running PC, but the
programmer Software is not started.
My programmer doesnât solves the last one...
May be you will be able to solve this problems better with your new
programmer. Which PIC types you plan to support and what software are
you
going to use ?
Are there recommended connector and pinout for in-circuit PIC
programming?
<snip stuff...>
>I am using this programmer for 'in-circuit' programming.
>After a while, I discovered this problems:
>
>What happens on the programmers outputs, if :
>* The programmer is powered, but not connected to the PC
>* The programmer is powered and connected to the PC, which is off
>* The programmer is powered and connected to a running PC, but the
> programmer Software is not started.
These are the reasons why I am going to develop my own. Actually, I wanted
to put the programmer in-circuit, just as you are.
My design point is for the programmer to stand alone and power the prototype
circuit (with a wall-wart - maybe you buy them at "Wal-Mart"? Sorry...)
with a 7805 (To be able to source at least a couple of hundread mAs).
Actually, my design requirements are:
1. Provide a socketed PIC for allowing pulling it in and out. With this, I
wanted the clocking and reset on the card so I don't have to set it up
anywhere else.
2. Use a ZIF Socket for the PIC (only 18 pin). This is a big point and the
Augat ZIFs I was able to get have 0.040" wide pins which are too big for
most protoboard sockets. Actually, right now I am using the ZIF plugged
into an 18 pin DIP socket, plugged into a Protoboard.
3. Have the socketed PIC Signals available on a 0.100" header so it can be
plugged into a protoboard easily.
4. Have the socketed PIC assembly provide power to the protoboard. This is
why I want to plug in a Wall-Wart to provide power.
5. Allow the socketed PIC to run even if the Host PC isn't up and running.
6. Allow the PIC to be programmed In the development Circuit.
7. The programmer should communicate with the PC via a Serial Port, not a
parallel port.
8. Provide RS-232 TX/RX for a cheap and easy way of providing a
debug/communications port to the PIC.
9. Support/Program the C61/C71/C84 (all the 18 pin 14 bit PICs).
>My programmer doesn't solves the last one...
So, your three "problems" would be encompassed by my design.
On most RS-232 DIY Programmers, TX is used as a clocking/data signal which
is not acceptable for my design point of wanting to be able to communicate
via RS-232.
I didn't want to go with a parallel port programmer for two reasons. The
first is, is basically cost - I don't want to get another parallel port for
my PC.
The second should be more obvious; by using an RS-232 Port, I have a cheap
and easy way of providing a debug interface (I'm using HyperTerminal under
Win/95 which doesn't cost anything and I don't have to write anything on the
PC side). Up to now, I have been using LEDs to tell me what's going on.
I'm sick of doing that and I thought a direct RS-232 Interface would be
better with english (or at least my version of it) messages coming out of
the program.
I know I still have to write the PC/16C54 Programming/Control Software, but
I don't see it as being a major hardship.
>Are there recommended connector and pinout for in-circuit PIC
>programming?
The 16C54 will have interfaces to RB6, RB7, and _MCLR as well as be able to
control power and the _MCLR Voltage. As far as I can tell, this is it.
When the PIC is being programmed or it's power is off, I will assert the
external reset line (to make sure nothing is driving the Socketted PIC -
although this will be up to the circuit designer to make sure this is
happening).
Today, the commercial sector is advancing computer and communication
technology at a breakneck pace. In 1992, optical fiber was being installed
within the continental U.S. at rates approaching the speed of sound (if
computed as total miles of fiber divided by the number of seconds in the year).
Aviation Week and Space Technology, October 28, 1996
> I think I would go with your suggestion. I presume the circuit would be:
>
> ______
> +15V-----+----------| 7812 |-----+--------------------+ +--- To Pwr
> | |______| | | | Control
> ---Filter | ---Filter \| -
> ---Cap - ---Cat | ^
> | ^Diode | /| |
> | | | | |
> +--------------+--------+ | +--- To +5V
> | To PIC
> Gnd to be
> Programmed
>
> For the Programming Voltage?
It seems you placed the diode upside-down in your diagram. If you use
several diodes in the bias path of a series regulator, remember they
reduce stability.
I wouldn't recommend using an optoisolator this way. It may work, but
you will have problems staying within specs. The C84 requires a Vpp
rise time of 1us. Optoisolators which have such short rise times are
usually for lower voltages and rarely accept 12V Vce. Also, they have low
CTR (current transmission ratio), which means you have to send a lot
of current through the primary side to get anything out of the
secondary side. For non-C84 PICs with higher Ipp, the current limit
for the diode might be exceeded.
The rise time is something to keep in mind. I know a report of
problems with the AN-589 due to slow switching. (The programmer ended
up programming from location 1 instead of 0.) I agree with Jim's
suggestion of going with PNP transistors, but even there you have to
be careful.
Cheers,
-- Martin
Martin Nilsson http://www.sics.se/~mn/
Swedish Institute of Computer Science E-mail: spammnspam_OUTsics.se
Box 1263, S-164 28 Kista Fax: +46-8-751-7230
Sweden Tel: +46-8-752-1574
Hi again,
One of my current PIC projects includes high voltage (+/-100V) supplies
derived from 110VAC mains. Recently there was some discussion here about
isolation vs non-isolation (I am 100% in favor of isolation for this
application as it can not be totally insulated). There was discussion about
using capacitive isolation instead of an isolation transformer. Has anyone
done something like this for higher currents (>1 amp)?? I would appreciate
any pointers or success/failure stories. Thanks.
Mark A. Corio
Rochester MicroSystems, Inc.
200 Buell Road, Suite 9
Rochester, NY 14624
Tel: (716) 328-5850 --- Fax: (716) 328-1144 http://www.frontiernet.net/~rmi/
***** Designing Electronics For Research & Industry *****
part 0 1294 bytes ----------
De: Mark A. Corio[SMTP:STOPspamMcoriospam_OUTspamBeGoneAOL.COM]
Enviado: martes 10 de diciembre de 1996 20:45
Para: Multiple recipients of list PICLIST
Asunto: Capacitive isolated power
Hi again,
One of my current PIC projects includes high voltage (+/-100V) supplies
derived from 110VAC mains. Recently there was some discussion here about
isolation vs non-isolation (I am 100% in favor of isolation for this
application as it can not be totally insulated). There was discussion about
using capacitive isolation instead of an isolation transformer. Has anyone
done something like this for higher currents (>1 amp)?? I would appreciate
any pointers or success/failure stories. Thanks.
Mark A. Corio
Rochester MicroSystems, Inc.
200 Buell Road, Suite 9
Rochester, NY 14624
Tel: (716) 328-5850 --- Fax: (716) 328-1144 http://www.frontiernet.net/~rmi/
***** Designing Electronics For Research & Industry *****
----------------------------
Thanks for all - Mil gracias
----------------------------
Eduardo Jorge Mart’nez VŽlez
a Asesoria
& &
s Sistematizacion
INET: spam_OUTejmvspamBeGonesatlink.com EraseME73070.3653KILLspamcompuserve.com
CServe: 73070,3653
2000-Rosario-SF-Argentina
TelFax: (54)(41)254561
Tel: (54)(41)8804
----------------------------
>Hi again,
>One of my current PIC projects includes high voltage (+/-100V) supplies
>derived from 110VAC mains. Recently there was some discussion here about
>isolation vs non-isolation (I am 100% in favor of isolation for this
>application as it can not be totally insulated). There was discussion about
>using capacitive isolation instead of an isolation transformer. Has anyone
>done something like this for higher currents (>1 amp)?? I would appreciate
>any pointers or success/failure stories. Thanks.
>
Hi Mark:
I haven't done it. But I did look into it, for a project that needed only
about 5 mils at 12 volts. And I also investigated the devices from Harris
and SGS that purport to be one-chip solutions.
With the straight capacitive approach, if you do the math for the current
you need, the required cap will be larger and more expensive than a
transformer. Also, the value of "isolation" is primarily that of limiting
the amount of current that would be available to sink into a hapless body
that might contact it. Having one amp available kind of strains the
concept. Too bad you have to have isolation; with the small amount of
voltage to be dropped in your application, a simple 10W resistor for each
supply would probably do it.
Mark A. Corio wrote:
>
> Hi again,
> One of my current PIC projects includes high voltage (+/-100V) supplies
> derived from 110VAC mains. Recently there was some discussion here about
> isolation vs non-isolation (I am 100% in favor of isolation for this
> application as it can not be totally insulated). There was discussion about
> using capacitive isolation instead of an isolation transformer. Has anyone
> done something like this for higher currents (>1 amp)?? I would appreciate
> any pointers or success/failure stories. Thanks.
>
> Mark A. Corio
> Rochester MicroSystems, Inc.
> 200 Buell Road, Suite 9
> Rochester, NY 14624
> Tel: (716) 328-5850 --- Fax: (716) 328-1144
> http://www.frontiernet.net/~rmi/
>
> ***** Designing Electronics For Research & Industry *****
Capacitive isolation, I think you've got your wires crossed
Caps can isolate DC not AC
The only practical way to isolate mains is via a transformer
A power supply using caps for isolation would only be possible
using very high frequence. It would cost more and would
have limited isolation only
As you say your app. cannot be totally isolated then
a transformer looks like the only option
--
Peter Cousens
email: EraseMEpeterRemoveMEcousens.her.forthnet.gr
snailmail: Peter Cousens, karteros, Heraklion, Crete, 75100, Greece,
phone: + 3081 380534, +3081 324450 voice/fax
After Bill Gates announced to the world that he was Microsoft,
his wife was asked to comment. She said that as his wife, she
had been the first to notice this problem
> With the straight capacitive approach, if you do the math for the current
> you need, the required cap will be larger and more expensive than a
> transformer. Also, the value of "isolation" is primarily that of limiting
> the amount of current that would be available to sink into a hapless body
> that might contact it. Having one amp available kind of strains the
> concept. Too bad you have to have isolation; with the small amount of
> voltage to be dropped in your application, a simple 10W resistor for each
> supply would probably do it.
The problem with using any type of transformerless power supply in a device
is that ANY electrical connection (intentional or unintentional) between
that device and anything that's ground- or mains-relative (or between that
device and any other device with an intentional or unintentional connection,
etc...) poses a severe risk of blowing up one or both devices.
If you are designing an alarm clock which is fully enclosed in a plastic
case, the series-capacitor trick might be just the ticket if your displays
don't need much current. If, however, you try to add a serial port to your
alarm clock, that port may have 120volts riding on its "ground" pin. Even
if you put caps on both sides of your supply, tying ground of the device to
earn ground could cause twice as much current to go through the caps as is
suppose to. Bad...
Personally, I'm just hoping someone will produce a small wall-dimple (smaller
than a wall-wart) with an unregulated 100KHz oscillator driving a small
transformer. I think such a thing should be produceable cheaper than normal
wall warts (the cost of the electronics should be offset by the use of a
smaller transformer) but I have not seen this done; the only similar thing
I've heard about was one which produced a regulated output (and cost an arm
and a leg); I would think that an unregulated output could be much much chea-
per.
>> With the straight capacitive approach, if you do the math for the current
>> you need, the required cap will be larger and more expensive than a
>> transformer. Also, the value of "isolation" is primarily that of limiting
>> the amount of current that would be available to sink into a hapless body
>> that might contact it. Having one amp available kind of strains the
>> concept. Too bad you have to have isolation; with the small amount of
>> voltage to be dropped in your application, a simple 10W resistor for each
>> supply would probably do it.
>
>The problem with using any type of transformerless power supply in a device
>is that ANY electrical connection (intentional or unintentional) between
>that device and anything that's ground- or mains-relative (or between that
>device and any other device with an intentional or unintentional connection,
>etc...) poses a severe risk of blowing up one or both devices.
>
>If you are designing an alarm clock which is fully enclosed in a plastic
>case, the series-capacitor trick might be just the ticket if your displays
>don't need much current. If, however, you try to add a serial port to your
>alarm clock, that port may have 120volts riding on its "ground" pin. Even
>if you put caps on both sides of your supply, tying ground of the device to
>earn ground could cause twice as much current to go through the caps as is
>suppose to. Bad...
>
>Personally, I'm just hoping someone will produce a small wall-dimple (smaller
>than a wall-wart) with an unregulated 100KHz oscillator driving a small
>transformer. I think such a thing should be produceable cheaper than normal
>wall warts (the cost of the electronics should be offset by the use of a
>smaller transformer) but I have not seen this done; the only similar thing
>I've heard about was one which produced a regulated output (and cost an arm
>and a leg); I would think that an unregulated output could be much much chea-
>per.
Hi John,
On a recent project, we used the Power Integrations TopSwitch, this comes
in various versions. but the one we used was the TOP202YAI.
It is a three terminal device, will run off 85-265V AC (rectified) and can
produce up to 24 watts. (24V 1A for our application). Some of their other
devices can handle more power. It was very easy to use, once we
got the transformer winding sorted out. Sorry I can't recall the pricing
at this instant, but they were relatively inexpensive.
It requires very few external components and so far has been suprisingly rugged
One customer forgot neutral on a 415V 3 Phase supply and put 415 across the
chip. Blew a few fuses but the topswitch survived.
Sorry I don't have a web address, but they are in Mountain View CA.
> The only practical way to isolate mains is via a transformer
> A power supply using caps for isolation would only be possible
> using very high frequence. It would cost more and would
> have limited isolation only
> As you say your app. cannot be totally isolated then
> a transformer looks like the only option
^^^^
What's about a light source (light-bulb connected to AC) and some
solar-cells ? :-)
I'd be careful when using a cap to tap off of line voltage.
When I design anything I always think about stray bandwidth - do I
have more than I need? If so, how are the various impedances in my
circuit going to respond to it?
Ideally, any supply that takes line voltage and steps it down would
limit the bandwidth to as low as your circuit could tolerate (it would
be a low pass filter). By limiting the bandwidth you'd cut down the
RF, ESD, and transient-type problems in your circuit.
With a series cap as the voltage dropping element you'd have a high
pass filter - the higher the frequency - the easier it would conduct.
ESD, RF, Line spikes would all eat you alive unless you put a low-pass
filter after the cap.
>
> On Tue, 10 Dec 1996, peter cousens wrote:
>
> > Mark A. Corio wrote:
> > >
> > > Hi again,
>
> [...]
>
> > The only practical way to isolate mains is via a transformer
> > A power supply using caps for isolation would only be possible
> > using very high frequence. It would cost more and would
> > have limited isolation only
> > As you say your app. cannot be totally isolated then
> > a transformer looks like the only option
> ^^^^
>
> What's about a light source (light-bulb connected to AC) and some
> solar-cells ? :-)
>
> bye
>
> Bernhard Schweighofer alias @spam@schweigiSTOPspamsbox.tu-graz.ac.at
> (Student at Graz University of Technology, Austria)
After Bill Gates announced to the world that he was Microsoft,
his wife was asked to comment. She said that as his wife, she
had been the first to notice this problem
>
> Maybe I didn't understand the question but...
>
> I'd be careful when using a cap to tap off of line voltage.
>
> When I design anything I always think about stray bandwidth - do I
> have more than I need? If so, how are the various impedances in my
> circuit going to respond to it?
>
> Ideally, any supply that takes line voltage and steps it down would
> limit the bandwidth to as low as your circuit could tolerate (it would
> be a low pass filter). By limiting the bandwidth you'd cut down the
> RF, ESD, and transient-type problems in your circuit.
>
> With a series cap as the voltage dropping element you'd have a high
> pass filter - the higher the frequency - the easier it would conduct.
> ESD, RF, Line spikes would all eat you alive unless you put a low-pass
> filter after the cap.
>
> It doesn't seem safe.
>
> ... just my impression...
>
> Jon Bertrand
> spam_OUTjonbspam.....cirris.com
As indicated in earlier msgs this subject:
1. You should include some series resistance in the circuit. Use at
least 100 Ohms for 120VAC and 200 Ohms for 230VAC. The resistor(s) must
have good surge current capabilities, i.e., do NOT use small thickfilm
chip resistors or metal film. Use a combination of parallel chip
resistors (say 3 each 300 Ohm 1206s), carbon comp, or wirewound.
2. There are literally millions of capacitor power supplies in everyday
use.....
3. Transformers are only as good as their insulation, too.
4. Yes, it's too true that any connections made to the circuit are not
isolated. Do not use capacitor power supplies unless all circuits are
self-contained. You will find that consumer products that have external
connections for microphones, earphones, serial ports, and so on, are
ALWAYS powered by transformers.
Enough said.
--
Paul Mathews, consulting engineer
AEngineering Co. optoeng.....@spam@whidbey.com
non-contact sensing and optoelectronics specialists
> Personally, I'm just hoping someone will produce a small wall-dimple (smaller
> than a wall-wart) with an unregulated 100KHz oscillator driving a small
> transformer. I think such a thing should be produceable cheaper than normal
> wall warts (the cost of the electronics should be offset by the use of a
> smaller transformer) but I have not seen this done; the only similar thing
> I've heard about was one which produced a regulated output (and cost an arm
> and a leg); I would think that an unregulated output could be much much chea-
> per.
"They" already have invented such a device. The company is Power
Integrations, Inc. They have a range of three-terminal off-line PWM
switching regulators. Most of them are in TO-220 packages. I'm not
sure how much your arms and legs are worth, but I was quoted "very
reasonable" prices for the PWR-TOP204YAI. (Very reasonable means that
I don't remember the price, but it was cheap enough for me to include
it in a design.)
Their phone number is (or at least used to be): (415) 960-3572.
In a message dated 96-12-11 09:57:01 EST, you write:
>What's about a light source (light-bulb connected to AC) and some
>solar-cells ? :-)
My application requires much more current than a solar panel of reasonable
size can produce from any light source.
Mark A. Corio
Rochester MicroSystems, Inc.
200 Buell Road, Suite 9
Rochester, NY 14624
Tel: (716) 328-5850 --- Fax: (716) 328-1144 http://www.frontiernet.net/~rmi/
***** Designing Electronics For Research & Industry *****
to which Peter scolded Bernhard with
> for 1A, get real!!
Lighten up! I was amused by this tongue-in-cheek suggestion. When you
consider the few % efficiency of incandescent bulbs, the low (10%)
efficiency of solar cells, the transmission efficiency (<5%) it all
adds up to a ludicrous image of hulking 3-phase supplies being used to
feebly illuminate a few LEDs, albeit at 50KV+ isolation!
Now for my own wacky idea: microwaves! Use old uwave oven magnetron,
transmit down waveguide (or between parabolic reflectors for that
megavolt isolation), receive in 1/4 wave antenna and rectify using a
swag of hot carrier diodes.
Back to reality, another way of obtaining galvanically isolated supply
is with piezoelectric 'transformers'. I remember this from the NatSemi
Linear Applications Handbook, but can't remember whether 1A could be
obtained. The piezo transformer had advantages of very high isolation
voltage and very low capacitive coupling. The disadvantages are the cost
of large chunks of PZT, fragility, low power-to-weight ratio and
complexity of the HF driving circuitry.
>
> Maybe I didn't understand the question but...
>
> I'd be careful when using a cap to tap off of line voltage.
>
> When I design anything I always think about stray bandwidth - do I
> have more than I need? If so, how are the various impedances in my
> circuit going to respond to it?
>
> Ideally, any supply that takes line voltage and steps it down would
> limit the bandwidth to as low as your circuit could tolerate (it would
> be a low pass filter). By limiting the bandwidth you'd cut down the
> RF, ESD, and transient-type problems in your circuit.
>
> With a series cap as the voltage dropping element you'd have a high
> pass filter - the higher the frequency - the easier it would conduct.
> ESD, RF, Line spikes would all eat you alive unless you put a low-pass
> filter after the cap.
>
> It doesn't seem safe.
>
> ... just my impression...
>
> Jon Bertrand
> spamjonbKILLspam@spam@cirris.com
I agree you need a transformer if you have for instance lines from your
circuit to the outside like all of mine.What I would like to find is a
transformer that is sized for a 20ma load (miniscule) the ones I am
using take up most of the board space in my designs. Tony M.
>
> Maybe I didn't understand the question but...
>
> I'd be careful when using a cap to tap off of line voltage.
>
> When I design anything I always think about stray bandwidth - do I
> have more than I need? If so, how are the various impedances in my
> circuit going to respond to it?
>
> Ideally, any supply that takes line voltage and steps it down would
> limit the bandwidth to as low as your circuit could tolerate (it would
> be a low pass filter). By limiting the bandwidth you'd cut down the
> RF, ESD, and transient-type problems in your circuit.
>
> With a series cap as the voltage dropping element you'd have a high
> pass filter - the higher the frequency - the easier it would conduct.
> ESD, RF, Line spikes would all eat you alive unless you put a low-pass
> filter after the cap.
>
> It doesn't seem safe.
>
> ... just my impression...
>
> Jon Bertrand
> jonbspamTakeThisOuTcirris.com
In practical circuits a resistor would also be used,
usually a cap in one side and a 100/200 ohm resistor in
the other side the resistor would also act as a fuse
This circuit is widely used in plug in industrial
timers and the like, that invariabily have undedicated
relay outputs
--
Peter Cousens
email: RemoveMEpeterRemoveMEcousens.her.forthnet.gr
snailmail: Peter Cousens, karteros, Heraklion, Crete, 75100, Greece,
phone: + 3081 380534, +3081 324450 voice/fax
After Bill Gates announced to the world that he was Microsoft,
his wife was asked to comment. She said that as his wife, she
had been the first to notice this problem
>.... There was discussion about
> using capacitive isolation instead of an isolation transformer.
Mark, the techniques that was being discussed did not isolate the cicuit
from teh mains; it simply used a capacitor to drop the applied voltage to a
managable value. This technique relies on the series capactive reactance of
the capactor, instead of teh turns ratio of the transformer.
The capacitor will *not* give you isolation from the mains, since it is AC
you are conducting, and it passes through the capacitor ... otherwise it
could not work. The transformer provides isolation because the two windings
are physically insulated, and the energy transfer between them happens by
virtue of the coupling the magnetic flux from one winding to the other.
>> What was used in High voltage circuits where only low voltages were
>> available in DC such as in cars was another device called a vibrator
>> which was a can about 1" dia and 2" long that had what was mostly a
>> relay that would be made to cut its own power on energising so it
>> would buzz, mass added to the armature allowed the resonant mode of
>> vibration to be adjusted to 50, 60 or 400 Hz (or what you wanted
>> even a few kHz) and the vibrator would have some extra contacts that
>> could be used in a push-pull arrangement to drive a transformer with
>> alternating polarity.
>
>Did the things really need precisely-tuned AC, or did they just need high
>voltage? If the latter, I'd think just using a highly-inductive relay coil
>would do the trick (since its flyback energy could go to hundreds of volts).
>Any idea if people ever did such nasty things?
The armature of the vibrator was mechanically resonanated to minimize the
energy needed to drive the coil. The transformer secondary was often tuned
with a capacitor to maximize the voltage output.
These radios often featured another vanished device: the cold-cathode gas
rectifier. The OZ4 didn't require a heated cathode, so used less power. But
they were notorious for their flakiness.
PICs are pretty straightforward compared to those dinosaurs.
Reg Neale
"Politics is the art of preventing people from taking part in affairs which
properly concern them." . . . .Paul ValŽry, 1943
>>The problem with using any type of transformerless power supply in a device
>>is that ANY electrical connection (intentional or unintentional) between
>>that device and anything that's ground- or mains-relative (or between that
>>device and any other device with an intentional or unintentional connection,
>>etc...) poses a severe risk of blowing up one or both devices.
I am confused by this. Aren't PC power supplies transformerless?
Why aren't they dangerous?
> I am confused by this. Aren't PC power supplies transformerless?
> Why aren't they dangerous?
because they do have a transformer between the High Voltage section and
the outputs :) The feedback for the voltage regulator is also
insulated, either with a transformer or with an optocoupler.
Luigi
-----------------------------+--------------------------------------
Luigi Rizzo | Dip. di Ingegneria dell'Informazione
email: TakeThisOuTluigispamiet.unipi.it | Universita' di Pisa
tel: +39-50-568533 | via Diotisalvi 2, 56126 PISA (Italy)
fax: +39-50-568522 | http://www.iet.unipi.it/~luigi/
_____________________________|______________________________________
> >>The problem with using any type of transformerless power supply in a device
> >>is that ANY electrical connection (intentional or unintentional) between
> >>that device and anything that's ground- or mains-relative (or between that
> >>device and any other device with an intentional or unintentional connection,
> >>etc...) poses a severe risk of blowing up one or both devices.
>
> I am confused by this. Aren't PC power supplies transformerless?
> Why aren't they dangerous?
The PCs uses a switching power source with a transformer, but this
transformer is for a frequency much more greater than 50Hz (ie 20KHz) so the
transformer is a little one with a ceramic core.
SET
--------------- 0 --------------------------------
Salvador Eduardo Tropea (SET).
Address: Curapaligue 2124, Caseros, 3 de Febrero
Buenos Aires, (1678), ARGENTINA
TE: +(541) 759 0013
>> I am confused by this. Aren't PC power supplies transformerless?
>> Why aren't they dangerous?
>because they do have a transformer between the High Voltage section and
>the outputs :) The feedback for the voltage regulator is also
>insulated, either with a transformer or with an optocoupler.
Oh that's right. They rectify the AC line to high voltage DC and
then chop that at high frequency through a transformer that can
be much smaller due to the higher frequency. I had forgotten.
Thanks!
> >>The problem with using any type of transformerless power supply in a device
> >>is that ANY electrical connection (intentional or unintentional) between
> >>that device and anything that's ground- or mains-relative (or between that
> >>device and any other device with an intentional or unintentional connection,
> >>etc...) poses a severe risk of blowing up one or both devices.
>
> I am confused by this. Aren't PC power supplies transformerless?
> Why aren't they dangerous?
>
> --
> Best regards,
> Andy Burgess
> spamBeGoneaabKILLspamcichlid.com
>
There is a SMALL transformer in the power supplies that provides isolation
and voltage reduction. The AC mains input is first rectified and filtered
to produce a high DC voltage and then a switching transistor is used to
produce a high frequency AC input to the transformer. Feedback for
regulation and control is done with either an optoisolator and/or another
tiny transformer.
The high switching frequency allows using such a small transformer.
73 de WA0ZNL
------------------------
Lynn Richardson
Progress Intrument, Inc.
I am currently designing a board with a hc11 as a main processor. But i
don't know
what the state of the output lines are after power up. I hope that they are
low but I can't find anny info on the subject.
>what the state of the output lines are after power up. I hope that they are
>low but I can't find anny info on the subject.
What port are you talking about ?
All port are in high impedance input state at reset, this is the normal
situation after a reset, specially for a HC11. But it's also true for
many other microcontroller, because the chip designer doesn't know
what it is connected to.
>what the state of the output lines are after power up. I hope that they are
>low but I can't find anny info on the subject.
What port are you talking about ?
All port are in high impedance input state at reset, this is the normal
situation after a reset, specially for a HC11. But it's also true for
many other microcontroller, because the chip designer doesn't know
what it is connected to.
> >what the state of the output lines are after power up. I hope that they are
> >low but I can't find anny info on the subject.
>
> What port are you talking about ?
> All port are in high impedance input state at reset, this is the normal
> situation after a reset, specially for a HC11. But it's also true for
> many other microcontroller, because the chip designer doesn't know
> what it is connected to.
On chips whose pins are all programmable as inputs or outputs, it is customary
to have all pins set to inputs on reset. There are, however, a few notable
exceptions:
[1] On the HC11 (your original query) I believe one of the I/O ports is output
only and defaults to being high (significantly pulled) on reset.
[2] On the PICs, all pins are tri-stated, but on some PICs certain pins may
default to analog inputs rather than digital ones; reading port A on the
16C62x, for example, requires enabling the digital inputs.
*CONFUSION ALERT* You do not have to enable the digital inputs on the
16C62X port A in order to output stuff there, BUT any BSF/BCF, etc. on
port A will clear any output whose corresponding input is not enabled.
This can be *VERY CONFUSING* if you aren't expecting it.
[3] On the Intel 8x51 and related chips, all of the I/O's are either open-
collector outputs or else open-collector outputs with weak pull-ups; they
default to being high on reset (which is to say, for most of them, not
quite tri-stated. Note that this means 8x51 outputs cannot directly con-
trol any type of power device safely since it's impossible to cover your
bases both in the power-failed and power-up-reset states.
[4] One bizarre exception to the rule about 8x51 I/O's is the Philips 87C575.
This one defaults to having all of its outputs pulled hard low on reset.
Wierd.
rowland.org.
