I'm quite new to the world of PICs, and I've got a couple of (hopefully
simple) questions about the PIC16C71...
1. When a pin is configured as an analog input, can it still be used as
a digital output? Or would you first have to reconfigure it as
digital I/O? The reason why I ask, is that it appears that RA1
can set up as digital I/O only if RA0 is also.
2. If you write a digital 1 or 0 to a pin which is configured as an
analog input (and has a voltage connected to it), will it damage the
PIC? Or will the digital output just be ignored by the PIC?
3. The databook states that an analog input reads as a digital 0. Does
this mean it's not a good idea to do a BSF/BCF on PORT_A if you've
got one or more pins set up as analog inputs? I guess this kind of
ties into question #2, since (I think) it would cause 0's to be
output on all analog inputs.
4. Let's say I've got RA0 & RA1 set up as analog inputs, and RA2-RA4 as
digital I/O. What happens if I write to one of the digital outputs
on PORT_A while an A/D conversion is taking place? Will it cause an
incorrect value to be converted?
I hope these questions make some sense. Any responses will be greatly
appreciated.
Thanks,
--
- Richard Friesen Little Timmy took a drink,
(spam_OUTRichard_FriesenTakeThisOuTmindlink.bc.ca) But now he'll drink no more,
For what he thought was H2O
Was H2SO4
------------------------------------------------------------------------------
--
>
> I'm quite new to the world of PICs, and I've got a couple of (hopefully
> simple) questions about the PIC16C71...
>
>
> 1. When a pin is configured as an analog input, can it still be used as
> a digital output?
No.
> 2. If you write a digital 1 or 0 to a pin which is configured as an
> analog input (and has a voltage connected to it), will it damage the
> PIC?
Since the digital output is disabled: No.
> 3. The databook states that an analog input reads as a digital 0. Does
> this mean it's not a good idea to do a BSF/BCF on PORT_A if you've
> got one or more pins set up as analog inputs?
No problem.
> 4. Let's say I've got RA0 & RA1 set up as analog inputs, and RA2-RA4 as
> digital I/O. What happens if I write to one of the digital outputs
> on PORT_A while an A/D conversion is taking place? Will it cause an
> incorrect value to be converted?
No promise, but I don't see any reason why it should. If you want
your conversion to be as good as possible Microchip recomends
executing a "sleep" directly after the conversion is started. The end
of conversion interrupt will wake the PIC up. This however gives you
problem with defining the sampling rate (since the conversion then
has to be internally RC-timed) which is crucial for calculating the
anti-aliasing filter you need.
I'm quite new to the world of PICs, and I've got a couple of (hopefully
simple) questions about the PIC16C71...
1. When a pin is configured as an analog input, can it still be used as
a digital output? Or would you first have to reconfigure it as
digital I/O? The reason why I ask, is that it appears that RA1
can set up as digital I/O only if RA0 is also.
2. If you write a digital 1 or 0 to a pin which is configured as an
analog input (and has a voltage connected to it), will it cause
excessive current and damage the PIC? Or will the digital output
just be ignored by the PIC?
3. The databook states that an analog input reads as a digital 0. Does
this mean it's not a good idea to do a BSF/BCF on PORT_A if you've
got one or more pins set up as analog inputs? I guess this kind of
ties into question #2, since (I think) it would cause 0's to be
output on all analog inputs.
4. Let's say I've got RA0 & RA1 set up as analog inputs, and RA2-RA4 as
digital I/O. What happens if I write to one of the digital outputs
on PORT_A while an A/D conversion is taking place? Will it cause an
incorrect value to be converted?
I hope these questions make some sense. Any responses will be greatly
appreciated.
Thanks,
--
- Richard Friesen Little Timmy took a drink,
(Richard_FriesenKILLspammindlink.bc.ca) But now he'll drink no more,
For what he thought was H2O
Was H2SO4
------------------------------------------------------------------------------
--
> 1. When a pin is configured as an analog input, can it still be used as
> a digital output? Or would you first have to reconfigure it as
> digital I/O? The reason why I ask, is that it appears that RA1
> can set up as digital I/O only if RA0 is also.
The manual claims not, but I think the original mask revision doesn't actually
work correctly. In several of my applications I've found that I have to set
the TRIS bits to configure the pin as a digital input. Otherwise the output
driver is enabled and fight my analog input. This completely contradicts the
description and the logic diagram in the data sheet.
> 2. If you write a digital 1 or 0 to a pin which is configured as an
> analog input (and has a voltage connected to it), will it damage the
> PIC? Or will the digital output just be ignored by the PIC?
I didn't get damage, although it might be possible. Just set the corresponding
bit in the TRIS register to a 1 to make the pin a digital input. Note that
even when you do this you can't actually _use_ it as a digital input if it
is configured as an analog input.
> 3. The databook states that an analog input reads as a digital 0. Does
> this mean it's not a good idea to do a BSF/BCF on PORT_A if you've
> got one or more pins set up as analog inputs? I guess this kind of
> ties into question #2, since (I think) it would cause 0's to be
> output on all analog inputs.
It's find to do a BSF or BCF on port A if the TRIS bits are set appropriately.
Just remember the usual caveats for using BSF & BCF on ports: the instruction
will read the logic levels at the pin (NOT the output register), and perform
the logic operation on those, and write the result to the output register.
This means that if you have a pin the PIC is trying to drive high, but external
loading is keeping it low, and you execute a BSF to set some other bit on the
port, the PIC will start trying to drive the first pin low.
> 4. Let's say I've got RA0 & RA1 set up as analog inputs, and RA2-RA4 as
> digital I/O. What happens if I write to one of the digital outputs
> on PORT_A while an A/D conversion is taking place? Will it cause an
> incorrect value to be converted?
Shouldn't affect it much, other than perhaps a tiny amount of noise (assuming
you have good grounding, etc.).
I was just thumbing through the Parallax catalog, and something
on p.20 (if you have it handy) caught my attention. This page lists the
entire BASIC Stamp instruction set. Under the heading "Analog I/O" it
lists the "POT" instruction, which it says "Reads a 5-50K potentiometer
and scales the result." Can someone tell me how this is done, since the
Stamp is really just a PIC16C56-XT/P, a resonator, and a serial EEPROM? I
didn't know there was a way to read a voltage level using a C56.
I am using a pic16c71. My goal is to be able to measure the voltage
created by a pot. How can I get the pot to show 0 to 5 volts as a
voltage dropper?
_____________________________________________________________________________
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Ben Kwok-Yiu Li wrote:
>
> I am using a pic16c71. My goal is to be able to measure the voltage
> created by a pot. How can I get the pot to show 0 to 5 volts as a
> voltage dropper?
Connect 1 end to ground, the other end to 5V, and the slider (center pin
on nearly all pots) to one of the A/D pins on the PIC. Also, I would
reccommend putting a 1K resistor between the slider and the PIC. This
will prevent the PIC from being damaged if the pin inadvertently gets set
as a digital output. A small capacitor (470 pF is a good value to start
with) will help keep the A/D from picking up noise. This is especially
important if the pot will be more than a couple of inches from the PIC,
or if there will be a lot of electrical noise. The reccommended circuit
is below:
The resistor and capacitor should be as close to the PIC as practical.
The value of the capacitor can be increased if the operating environment
is extremely noisy. The value of the pot should fall in the range from
1K to 100K. Lower values give better noise immunity but will dissipate
more power.
Greetings to all,
I'm very new to micro's and programming
Is there a simple way to read a 0-5v analogue input with the 16c84
any hints would be welcome
Kevin
One of the really cool things about the PIC16C622 is that it
has two analog comparators. They're very fast and work over the
entire temperature range (which includes the automotive temp
range!). However, there are a couple of short comings when you
wish to provide hysteresis. And considering that about 99.7% to
99.8% of the time I use an analog comparator I also design it
such there is some hysteresis, this makes the 622 comparators
a little difficult to use.
There are essentially two ways to provide hysteresis:
1) Apply positive feedback to the positive terminal
2) Apply negative feedback to the negative terminal
For example, if your reference voltage is on the "+" terminal
of the comparator and your signal is applied to the "-" terminal,
then you can either feed a portion of the comparator's output
back to the positive terminal or you can invert the comparator's
output and feed it back to the negative terminal. The latter
case is the only one available when using the 622's, and is
shown below:
U1 is the comparator, U2 is an inverter. The Vref,R1,R2 circuit
can also be the internal 622 voltage reference (but you could just
as well use an external one). R3 and R4 form the hysteresis circuit.
Actually, I should be a little more specific. There are really eight
different ways to configure the PIC16C622 analog comparators. However,
if you wish to use both comparators and have totally separate hysteresis
circuits for each one, then you're confined to the configuration shown
above.
Now the question... Part 1) Has anybody else dealt with this issue and
2) What did you use for the inverter?
FYI 1, I have simulated this circuit using PSPICE. Since I want to use the
automotive temperature range, I cannot use the "standard" 74XX14 type IC's
(which are only good to at best the 80 degree C industrial temperature
range). I have used an NPN transistor (the infamous 2N3904) with quasi-
encouraging results.
FYI 2, AN611 is the only one that discusses 622's comparators. Unfortunately,
the author did not need hysteresis in his application ( one of those 0.03%
abnomalies I presume... actually, his signals were internally generated
and [I guess] less noisy then the typical case).
>One of the really cool things about the PIC16C622 is that it
>has two analog comparators. They're very fast and work over the
>entire temperature range (which includes the automotive temp
>range!). However, there are a couple of short comings when you
>wish to provide hysteresis. And considering that about 99.7% to
>99.8% of the time I use an analog comparator I also design it
>such there is some hysteresis, this makes the 622 comparators
>a little difficult to use.
If you were using one of the comparators with an interrupt, would
it be possible to reconfigure the reference voltage "on the fly"
to provide hysteresis? I don't know much about this part, and I breezed
through AN611 very quickly. The APP note says that the reference
divider is a 16 tap resistor network with a limited range, but
this may be OK for some applications.
See application note 512 and 513. You could also consider a on-chip ratiometric
serial A/D such as the Linear Tech LTC1096, 1098, 1291, and 1292. These parts
are very to interface. Are you aware of the PIC16C7x with built-in A/D?
Mike Riendeau wrote:
>
>
> If you were using one of the comparators with an interrupt, would
> it be possible to reconfigure the reference voltage "on the fly"
> to provide hysteresis?
Yes, but... Three minor problems. One, the settling time of the 622's
internal voltage reference circuit is relative slow (10 microseconds).
Second, any kind of "software hysteresis" will significantly reduce
the effective comparator speed. For example, the 622 comparators are
spec'd with a 400ns response time, where response time is measured
with "one of the inputs at (Vdd-1.5)/2 and the other transitioning
from Vss to Vdd". Now, even if the reference circuit had an
instantaneous response, the software overhead to change to a new
level would rapidly consume time that could be used for sampling.
(see FYI 4, below). Third, the same comparator is used by both
comparators. If you change the reference voltage for one then you
will affect the performance of the other.
FYI 4, I'm going to use the full bandwidth of these puppies (one
puppy == one comparator). The normal mode is quiescent which
means there is no signal and consequently no change of states
in the comparators outputs. When a signal occurs, it will last
for 100 microseconds or so. I'll catch the initial transition with
an interrupt (after a little of interrupt latency of course). I'll
sample the subsequent transitions once every 400ns.
FYI 5, I've used external comparators and PORT B's change on interrupt
capability with the approach discussed in FYI 4 with great success.
______________________________ Reply Separator _________________________________
Subject: Re: PIC16C622 & Analog Comparators
Author: pic microcontroller discussion list <KILLspamPICLISTKILLspamMITVMA.MIT.EDU> at
Address-InternetPO
Date: 8/7/96 5:02 PM
Mike Riendeau wrote:
>
>
> If you were using one of the comparators with an interrupt, would
> it be possible to reconfigure the reference voltage "on the fly"
> to provide hysteresis?
kevin harris wrote:
>
> Greetings to all,
> I'm very new to micro's and programming
> Is there a simple way to read a 0-5v analogue input with the 16c84
> any hints would be welcome
> Kevin
I'm not sure if this is what you mean when you say simple Kevin, but here is a
new approach to the solution. It's a 10 Cent answer and uses the Basic Stamp
'POT"
command. Don...
EASY PIC'n Beginners Guide to using PIC 16/17 MicroChip products.
Picosaurus(tm) 40 pin PICBasic with 8 channels of A-D, and real Uart.
PIC Basic Compiler. Programmers from 15 USD. Pic-Axe(tm) A New Tool.
Jon Bertrand wrote:
>
> Does the ref. voltage come out to and external pin (I'm guessing it
> doesn't or why would you be asking this)?
If you want it to, then yes it does. You should probably guess that it does
instead of it doesn't. Because..., suppose you wish to look at a "small"
AC signal, let's say +/- 100 mv for the sake of arguement. If you wish
to digitize it with the comparator, then you will want the signal's DC
component to equal the DC voltage of the reference. This way, the signal
will oscillate about the reference voltage; positive excursions will cause
the 622's comparator to go low and negative execursions will cause it to
go high. The polarity reversal is because reference voltage is internally
tied to the positive terminal of the comparator. (That is in the mode
that makes the comparators' outputs available for feedback). And when the
negative terminal is at a higher voltage then the positive terminal, the
output of the comparator is low.
Now, you can easily offset the AC signal with one capacitor and one resistor:
C
||
AC ----||----+--------- AC signal + DC offset
|| |
/
\ R
/
\
|
+------- Reference Voltage
R and C can be chosen such that they do not load the AC signal or the
reference voltage. There are a few details that I'm still glossing over,
but I think you get the idea.
> What kind of reference is it - does it have a sensitivity to VCC that
> could be exploited?
It's a 16 resistor voltage divider that is fed from Vdd. There is also another
resistor and switch that allows you to provide an additonal DC offset.
Take a look at the data sheet for more details. They describe the output voltage
as a function of the switch settings. If anyone is interested in the source
impedance as a function of the switches, I'll post those equations.
I am relatively new to PIC's. Using a part like the PIC16C84, what would be
the most straight forward way to interface to the TMP04 temperature sensor?
The TMP04 is a 3-wire device (+5v,gnd,data_out). The temperature is encoded
using ratiometric encoding. Basically what is done is that the data_out line
is held high for a certain period of time (T1) and held low for a certain
period of time (T2) and this repeats, over and over. To read the
temperature, you
measure the times T1 & T2 and plug them into the following formula:
F degrees = 455 - ((T1*720)/T2) (if memory serves....)
Anyway, I need to find the least complicated scheme to measure the two times
T1 and T2. I have looked at the sensor on a scope and manually calculated the
temperature and it was very close. The average timing is 35hz, so it is not
very high speed.
At 14:46 16/05/97 -0400, Carlton Haycock wrote:
>I am relatively new to PIC's. Using a part like the PIC16C84, what would be
>the most straight forward way to interface to the TMP04 temperature sensor?
>The TMP04 is a 3-wire device (+5v,gnd,data_out). The temperature is encoded
>using ratiometric encoding. Basically what is done is that the data_out line
>is held high for a certain period of time (T1) and held low for a certain
>period of time (T2) and this repeats, over and over. To read the
>temperature, you
>measure the times T1 & T2 and plug them into the following formula:
>
>F degrees = 455 - ((T1*720)/T2) (if memory serves....)
>
>Anyway, I need to find the least complicated scheme to measure the two times
>T1 and T2. I have looked at the sensor on a scope and manually calculated
the
>temperature and it was very close. The average timing is 35hz, so it is not
>very high speed.
Since the c/f84 don't have any fancy timer stuff, but have these
interrupt-on-change port b (bits 4..7), I'd probably put it on one of these
and on interrupt read the timer value. (You have to make sure that you take
care of the timer overflows: either handle them in a timer ov interrupt
routine, effectively creating a 16bit timer, or make sure the timer runs
slow enough to not overflow twice between two port interrupts.) The rest is
simple math, it seems.
(I have only _very_ limited and still mostly theoretical PIC knowledge... :-)
> At 14:46 16/05/97 -0400, Carlton Haycock wrote:
> >I am relatively new to PIC's. Using a part like the PIC16C84, what would be
> >the most straight forward way to interface to the TMP04 temperature sensor?
> >The TMP04 is a 3-wire device (+5v,gnd,data_out). The temperature is encoded
Or you can just sample the OP of the TMP03/4 and count the number of
highs in one register pai and lows in another, keep at it until one register
hits say 4096 or some other comfy number and then you have the ratio
as a function of 4096 in the other register. This method introduces jitter
but does not require any timing, just sort of regular polling of the
device and a long period to average out the jitter caused by the
non synchronous sampling a bit.
You can look at some examples in PC PASCAL and STAMPII BASIC on my projects
page.
there is a chip that is an analog delay chip. digikey carries them. i think
they might be refered to as bucket delay chips. it is basicly an analog
memory chip that shifts 1024 readings.
michael
At 07:56 AM 8/15/97 +0200, you wrote:
>Amos Ndegwa wrote:
>>
>> Someone to advise me on whether there is an IC(s) that can be used to
>> design/build an audio echo circuit with an adjustable time delay. (Not
to be {Quote hidden}
>> used on a computer)
>>
>> Thanks in advance
>>
>> Amos
>
>This could turn out to be a nice '74 project. Run a 16C74 @ 20MHz.
>Sample the
>audio and shove it into external RAM. Shift the entire contents and move
>it
>out to a DAC. Add this to the normal audio path.
>
>If you are going to use it for music, then :
>
>You shake it to the left, shake it to the right,
>sample at full speed, but use a PIC, al right?
>
>;)
>
>--
>Friendly Regards
>
>Tjaart van der Walt
>TakeThisOuTtjaartEraseMEspam_OUTwasp.co.za
In a message dated 97-08-15 03:08:24 EDT, you write:
<< there is a chip that is an analog delay chip. digikey carries them. i
think
they might be refered to as bucket delay chips. it is basicly an analog
memory chip that shifts 1024 readings.
michael
At 07:56 AM 8/15/97 +0200, you wrote:
>Amos Ndegwa wrote:
>>
>> Someone to advise me on whether there is an IC(s) that can be used to
>> design/build an audio echo circuit with an adjustable time delay. (Not
to be >>
Hello
The Bucket brigade devices are made by Reticon. I have used a very old
version of the 1024 bit device (SAD1024). It was very difficult to use.
Their newer parts are much easier to deal with. They come in all bit widths
(256, 512 and 1024).
The wider the bucket brigade the deeper the echo effect.
"David W. Duley" writes:
>The Bucket brigade devices are made by Reticon. I have used a very old
>version of the 1024 bit device (SAD1024). It was very difficult to use.
> Their newer parts are much easier to deal with. They come in all bit widths
>(256, 512 and 1024).
I had one of the old SAD1024 Reticon devices in 1979.
I remember that the clock required two signals which complimented each other
but that meant only that you had to use an inverter for one of the signals
and then feed the oscillator directly to the other clock input. I didn't
know that one could buy modern versions of the SAD1024. Mine worked very
nicely until I zapped it with static electricity through mishandling.
at $12.00, that was an expensive lesson.
What was bad about the older SAD1024's that has been corrected in
the present delay chips? I never tried to cascade a large number of them
or use then in anything sophisticated. All I did at the time was to
connect the two 512-bit halves of the chip together and then play with the
audio delay that resulted from the full 1024-bit register.
Martin McCormick WB5AGZ Stillwater, OK 36.7N97.4W
OSU Center for Computing and Information Services Data Communications Group
We need to implement some white noise using preferrably analog
circuitry. Is this easily achieved?
We are going to use it in a sound generation device (audio-purposes),
jam
it through some filters, creating some hopefully interesting effects :-)
I have seen some digital random generation algoritms, can these be used
in some clever way with a D/A-R-2R ladder to produce noise? And if so,
what kind of spectral distribution does this give?
Tricky questions? I don't have a clue.
I would be grateful for any pointers
Thanx in advance / Mattias Engstršm
(BTW, thanks for all the help I got on the RS232<->TTL level conversion)
On Wed, Oct 22, 1997 at 12:00:22AM +0100, Mattias Engstrvm wrote:
> We need to implement some white noise using preferrably analog
> circuitry. Is this easily achieved?
The usual technique is to reverse bias a Zener diode, and amplify the breakdown
noise. Unless you use a special noise diode, the noise spectrum will not be
perfect, but that's probably not an issue for your purpose.
You'll need to experiment with how much amplification is required - quite
likely you can get away with one op-amp stage.
We need to implement some white noise using preferrably analog
circuitry. Is this easily achieved?
Mattias,
One classic analog way is to amplify a reversed bias transistor (base and
emitter). There was a classic transistor that was used fairly widely, but
its part# escapes me at the moment. All transistors are not created equal
with regard to white noise quality from what I've read.
Try an internet search on PAIA (spelling?) Electronics, Thomas Henry, or
Polyphony magazine.
I owned a Kawai SX-210 synthesizer and it generated white noise via a
reversed-biased NPN transistor followed by two stages of amplification with
a TL082 op-amp. It may have used a 2SC536G transistor.
Hi there,
Can anyone recommend a distributor in Oz for Analog Devices ? (ic's)
Since Hartec lost the agency a while ago, supply has not been good.
A US distributor will do if no-one decent over here. I tried Digi-Key
as it seems to pop up on the list every so often but they don't seem
to support this brand. RS Components & Farnell are too expensive even
when buying in tube lots. Any hints would be appreciated. :-)
Thanks...
________________________________________________________________
Dave Duffy. Audio Visual Devices E-mail: RemoveMEAVDspam_OUTKILLspammailbox.uq.edu.au
Phone: +61 7 38210362 Facsimile: +61 7 38210281
Unit 8, 9-11 Trade Street, Cleveland Queensland 4163, Australia.
________________________________________________________________
At 10:39 PM 10/27/97 +1100, you wrote:
>Hi there,
>Can anyone recommend a distributor in Oz for Analog Devices ? (ic's)
>Since Hartec lost the agency a while ago, supply has not been good.
>A US distributor will do if no-one decent over here. I tried Digi-Key
>as it seems to pop up on the list every so often but they don't seem
>to support this brand. RS Components & Farnell are too expensive even
>when buying in tube lots. Any hints would be appreciated. :-)
Some say there is no magic but, all things begin with thought then it becomes
academic, then some poor slob works out a practical way to implement all that
theory, this is called Engineering - for most people another form of magic.
Massen
>
> Hi there,
> Can anyone recommend a distributor in Oz for Analog Devices ? (ic's)
> Since Hartec lost the agency a while ago, supply has not been good.
> A US distributor will do if no-one decent over here. I tried Digi-Key
> as it seems to pop up on the list every so often but they don't seem
> to support this brand. RS Components & Farnell are too expensive even
> when buying in tube lots. Any hints would be appreciated. :-)
> Thanks...
For years now I have been mainly dealing with digital electronics,
however my knowledge of analog and rf technoligies is extremely lacking. I
was wondering if anybody out there knows links to sites on the net that are
perfect for a begginner in analog and RF electronics. Thanks in advance for
any info. TTYL
> For years now I have been mainly dealing with digital electronics,
>however my knowledge of analog and rf technoligies is extremely lacking. I
>was wondering if anybody out there knows links to sites on the net that are
>perfect for a begginner in analog and RF electronics. Thanks in advance for
>any info. TTYL
I'm sure others will saturate you with links, so I'll just give you a few
of my favorite books, (the dog-eared ones).
The Forrest Mims Engineer's Notebook
by Forrest Mims
HighText Publications, 1992
ISBN: 1-878707-03-5
Forrest Mims' Circuit Scrapbook
by Forrest Mims
Howard W. Sams & Co., 1987
ISBN: 0-672-22552-2
CMOS Cookbook
by Don Lancaster
Howard W. Sams & Co., 1988
ISBN: 0-672-22459-3
IC Op-Amp Cookbook, 3rd Edition
by Walter G. Jung
Howard W. Sams & Co., 1986
ISBN: 0-672-22453-4
Forrest Mims' stuff is good, so are Don Lancaster's Cookbook series, and I
couldn't get by without Jung's book, but the best all around book on
electronics that I know is:
The Art of Electronics
by Paul Horowitz and Winfield Hill
Cambridge University Press, 1989
ISBN 0-521-37095-7
This book is encyclopedic and assumes no knowledge other than algebra for
the most part. Good beginner's stuff, but _great_ stuff for folks who've
been at this a while.
Be sure it's the _second_ edition, which came out in '89. It has a
companion "The Art of Electronics Student Lab Manual" (I believe that's the
title), too.
--BN
----------------------------------------------------------------------------
Country Robot "Modular robot components
69 S. Fremont Ave. # 2 for education and industry"
Pittsburgh, PA 15202
----------------------------------------------------------------------------
You listed some of my favorite books! ...Wish I'd found Horowitz & Hill
sooner, some of the books I got before it would not have been needed.
Though I'm still happy to have the Lancaster titles, Jung, etc.
Could you tell me what the Forrest Mims' Circuit Scrapbook is like? I have
his "Engineer's Notebook" (Hightext and R.S. versions) as well as the other
stuff he's done for R.S. Does the "Scrapbook" cover different territory?
I don't recall ever seeing that one.
> From: Robert Nansel <RemoveMEbnanselKILLspamNAUTICOM.NET>
> To: PICLISTSTOPspamspam_OUTMITVMA.MIT.EDU
> Subject: Re: Analog Electronics [OT]
> Date: Friday, December 05, 1997 8:14 PM
>
> I'm sure others will saturate you with links, so I'll just give you a few
> of my favorite books, (the dog-eared ones).
>
> The Forrest Mims Engineer's Notebook
> by Forrest Mims
> HighText Publications, 1992
> ISBN: 1-878707-03-5
>
> Forrest Mims' Circuit Scrapbook
> by Forrest Mims
> Howard W. Sams & Co., 1987
> ISBN: 0-672-22552-2
In message <01bd01e1$e067a480$76d1f5cf@cyrix-p166>, Herbert Graf
<spamBeGonehgrafSTOPspamEraseMEGEOCITIES.COM> writes
> For years now I have been mainly dealing with digital electronics,
>however my knowledge of analog and rf technoligies is extremely lacking. I
>was wondering if anybody out there knows links to sites on the net that are
>perfect for a begginner in analog and RF electronics. Thanks in advance for
>any info. TTYL
Buy The Art of Electronics, by Horowitz and Hill, and the ARRL Handbook
for Radio Amateurs.
> For years now I have been mainly dealing with digital electronics,
>however my knowledge of analog and rf technoligies is extremely lacking. I
>was wondering if anybody out there knows links to sites on the net that are
>perfect for a begginner in analog and RF electronics. Thanks in advance for
>any info. TTYL
I like the Linear Technology Application Handbooks, vols. I, II, and III.
(You can download the app notes from http://www.linear-tech.com, or just have them
send you the paper books.)
The National Semiconductor Linear Applications Handbook is another must-have.
Bob Pease's Troubleshooting Analog Circuits is good if you're going to be
building anything analog, but it's not as useful as the Art of Electronics
or the ARRL handbook as a learning reference.
If you enjoy the Jim Williams app notes in the LT books, you'll like Analog
Circuit Design: Art, Science, and Personalities.
[snip]
> If you enjoy the Jim Williams app notes in the LT books, you'll like
> Analog
> Circuit Design: Art, Science, and Personalities.
>
>
> later,
> newell
>
What an amazing book. It isn't a comprehensive tutorial but it is
pervaded with the 'spirit' of analogue circuit design. I got my copy
from Fry's in LA.
At 19:57 05.12.1997 -0500, you wrote:
> For years now I have been mainly dealing with digital electronics,
>however my knowledge of analog and rf technoligies is extremely lacking. I
>was wondering if anybody out there knows links to sites on the net that are
>perfect for a begginner in analog and RF electronics. Thanks in advance for
>any info. TTYL
maybe a book ?
Horowitz & Hill
The art of electronics
2nd edition
Cambridge
As a result of the glowing recommendations in this list, I went out
and bought a copy of The Art of Electronics a few months ago. I agree
that it is a very good book, but there are two other books that have
been around for years (mine is probably 20 years old and still
relevant) that are being overlooked.
The Radio Handbook
The ARRL Amateurs Handbook. (i think this is the name).
Of the two, I would recommend the Radio Handbook as the second book is
more specific to amateur radio.
IMHO, The Radio Handbook is actually a better tutorial and reference
than The Art of Electronics, and every few years it gets an "upgrade"
in the form of a new edition. I think my copy from 20 years ago was
the 20th edition. It covers everything from the basics up to
sophisticated analog and digital electronics, including obviously, RF,
and unlike The Art of Electronics, also includes some simple to
complex construction projects, including test gear.
Add to that a better reference section at the end of the book, and I
believe you have a superior "must have" guide for anyone involved in
electronics.
>At 19:57 05.12.1997 -0500, you wrote:
>> For years now I have been mainly dealing with digital electronics,
>>however my knowledge of analog and rf technoligies is extremely lacking. I
>>was wondering if anybody out there knows links to sites on the net that are
>>perfect for a begginner in analog and RF electronics. Thanks in advance for
>>any info. TTYL
>
>maybe a book ?
>
>Horowitz & Hill
>The art of electronics
>2nd edition
>Cambridge
>
>
>So long
>
>Thomas
>=8-)
>
>**********************************************************
>* Thomas Magin FON: ++49-761-4543-489 *
>* marquette-Hellige GmbH FAX: -507 *
>* Emergency Systems email: spamBeGonemaginKILLspamhellige.de *
>* Munzinger Str. 3 *
>* D-79111 Freiburg / Germany *
>**********************************************************
New Interesting PIC 16C84 Controlled Clock Now Simulate's an Analog
Clock
or scrolling text messages
Hello,
I made another propeller clock based on Bob Blick's idea
This time it could simulate an analog clock
it also can do the digital version of the clock
or scrolling text messages
if your interested you could take a look at
my experimental pages with pictures of the clock
Congratulations on a creating a truly magnificent icon of nerdmanship!
No really, I love it. I thought my solar-powered propeller beanie
concept would make me a geek amongst geeks, but that kind of clock
could be left upon my parent's mantelpiece to advertise their
son's cringing technogeekiness to any visitors they invite.
I mean, you can't ignore it whirring noisily away.
But wait! I've an idea, and its as hot as my pants!
Why not combine the two ideas into a head-mounted
propeller-beanie clock? The LED-bearing arms of your clock
hang down in front of the wearers eye's, indicating the time,
and scrolling text.
As a bonus, it would deter/swat most insects, and attract
fireflies to enhance your light show.
I've always thought that there is some sign above me (visible
only to women) saying "this person is an engineer, do not
date!" With the headware described above, I can display
any message I like! This could be the biggest thing since
pheromone sprays! Race you all to the patent office!
I am just beginning to dable into analog data acquisition with PIC's and
was wondering if anybody had any code snippits that would demonstrate
what needs to be done to do a simple analog in digital out with a
PIC16C74A. All I need would be a single sample, just to get me
started. Any help or direction would be greatly appreciated.
I need an analog expert to redesign a low-noise front end for medical
purposes (to measure EMG and EEG - signals in the low microvolt range). The
system we have has a million Megaohm (10^12) input impedance, 130dB CMRR,
and 12 bit resolution, but the signal waves around too much if the cables
are jiggled.
I have seen systems that somehow minimize this effect, and need someone who
could help redesign such a front end on a contract basis.
You don't really need to redesign the analog front-end - if I understand your
observations,
it is a cable problem. You need to use low microphonics or low piezoelectric
cables. Check on
the Net for low-microphonic-noise cables. The best I have used have a low
capacitance, low
piezoelectric coefficient insulator and carbon powder shield lubricant. I used
them for both
medical and seismic geophone transducer designs. I am assuming that you are
using electrode
gel, of course, to reduce the electrode motion noise and CMRR related 60 Hz
pickup.
Wayne Foletta
Design Engineer
Data Acquisition Products
SiliconSoft, Inc.
San Jose, CA http://www.siliconsoft.com
>
>I need an analog expert to redesign a low-noise front end for medical
>purposes (to measure EMG and EEG - signals in the low microvolt range). The
>system we have has a million Megaohm (10^12) input impedance, 130dB CMRR,
>and 12 bit resolution, but the signal waves around too much if the cables
>are jiggled.
>
>I have seen systems that somehow minimize this effect, and need someone who
>could help redesign such a front end on a contract basis.
>
>Craig Webb
>
I am trying to make analog control A/D generator. I connected
20 Mhz crystal with 16c71. on output I am getting only 20 Khz.
I know 20/4 = 5 Mhz do you think A/D conversion slowing it down.
Is there any thing I am doing wrong?
here is my code.
TMR0 EQU 0x01 ; COUNTER
PC EQU 0x02 ; PROGRAM COUNTER
STATUS EQU 0x03 ; STATUS REGISTER
FSR EQU 0x04 ; FILE SELECT REGISTER
PORTA EQU 0x05 ; OUTPUTS
PORTB EQU 0x06
RP0 EQU 0x05
TRISA EQU 0x05 ;
TRISB EQU 0x06 ;
OPTION_REG EQU 0x81 ;
ADCON0 EQU 0x08
ADCON1 EQU 0x08 ;
ADRES EQU 0x09
PCLATH EQU 0x0A
INTCON EQU 0x0B
CARRY EQU 0x00 ; CARRY BIT
DCARRY EQU 0x01 ; DIGIT CARRY BIT
PDOWN EQU 0x03 ; POWER DOWN BIT
WATDOG EQU 0x04 ; WATCHDOG TIMEOUT BIT
F EQU 0x01
Z EQU 0x02
PORTA EQU 0x05 ; PIN
PORTB EQU 0x06 ; INPUTS FROM DIP SWITCH
CH_1_RESOLT EQU 0x0C ; TEMP REGISTER
CH_2_RESOLT EQU 0x0D
CH_3_RESOLT EQU 0x0E
CH_4_RESOLT EQU 0x0F
COUNT EQU 0x1D
COUNT1 EQU 0x1C
TEMP EQU 0x1E
INIT CLRF PORTB
BANK1 ; SET UP PAGE 1
MOVLW B'00000000'
MOVWF TRISB ; B0 AND B1 INPUTS THE REST OUTPUTS
MOVLW B'00011111'
MOVWF TRISA ; SET AS INPUTS A4 OUTPUT
MOVLW B'00000000'
MOVWF ADCON1 ; SET A/D INPUTS ON A0/1 REST DIGITAL
BANK0 ; RETURN TO PAGE 0
MOVLW B'11000001' ; SET A/D INTERNAL RC CLOCK AND 11 FOR
CH 4
MOVWF ADCON0 ; DO IT
; ****************** THE START ************************
MAIN
BSF PORTB,2
BSF ADCON0,2 ; START CONVERSION
MOVLW 10 ; THIS LINE IS 10
MOVWF TEMP
DECFSZ TEMP,F ; WAIT A WHILE
GOTO $-1
BTFSC ADCON0,2 ; TEST FOR END OF CONVERSION
GOTO $-1
MOVF ADRES,W ; LOAD A/D RESULT INTO W
MOVWF CH_1_RESOLT ; STORE IT
BSF PORTB,0
CALL DELAY
BCF PORTB,0
CALL DELAY
GOTO MAIN
One thing that may be slowing down the program is that
you are starting the conversion and waiting for it
to complete before reading the A/D and doing the delay.
If you first read the A/D and then start the next conversion
before doing the delay, there would be much less, if any,
time spent waitting for the conversion to complete.
I have rearanged your code in the MAIN routine to do this.
I would arange the routines in a different order.
wait for A/D to complete
read A/D
select next A/D input (if necessary)
Delay for next input to settle (if changed A/D inputs)
start conversion
delay
This can all be done under interupt if you desire. It gets
a little complicated if you switch inputs. But there are no
wasteful delays necessary.
with no A/D input switching
INTERUPT wait for A/D to complete
read A/D
start next conversion * this gives one more cycle
store A/D reading * for conversion
set 'NEW' bit flag * to show main that new A/D reading
return from interupt
END INTERUPT
with A/D input switching
INTERUPT wait for A/D to complete
read A/D
select next A/D input * if posible before
store A/D reading * storing A/D reading
set 'NEW' and 'CONVERSION DELAY' bit flags
do something to show which A/D input had 'NEW' reading
and it would be nice to calculate the next-next A/D input
return from interupt
END INTERUPT
SUBRTN if 'CONVERSION DELAY' bit flag set
clear 'CONVERSION DELAY' bit flag
set 'START CONVERSION' bit flag
return from subroutine
else
clear 'START CONVERSION' bit flag
start conversion
return from subroutine
END SUBROUTINE
and in the main body of the program test for the bits
'CONVERSION DELAY' OR 'START CONVERSION' in the same
bit test in one instruction. if either is set, then call
SUBRTN. Just make sure that there is enuff cycles
between 'TEST's to let the A/D input settle, and that
the numbers of cycles between three 'TEST's calls are not
greater than the interupt timer.
It is necessary to have the two part routine to insure
that if an interupt occures just before a 'TEST' instruction,
there will be a delay before the conversion is started.
After writting this, I see another way to switch A/D inputs.
Just run the interupt timmer twice as fast and...
INTERUPT if 'START CONVERSION' bit flag clear
read A/D
select 'NEXT A/D INPUT'
store A/D reading
set 'NEW' and 'START CONVERSION' bit flags
indicate which A/D input is 'NEW' ('LAST A/D INPUT')
set 'START CONVERSION' bit flag
return from interupt
else (the bit is set)
start conversion * do this as soon as possible
clear 'START CONVERSION' bit flag
good place to move the 'NEXT A/D INPUT' pointer
into the 'LAST A/D INPUT' pointer, and calculate
'NEXT A/D INPUT' pointer
return from interupt
END INTERUPT
It may be best to have a 'NEW' bit flag for each A/D input
and a seperate register for each A/D input reading.
With this method there is an equal amount of time for
the input to settle and for the conversion to complete.
But still best to test for conversion compete before
reading it.
>* remove MOVLW 10 ; THIS LINE IS 10
>* remove MOVWF TEMP
>* remove DECFSZ TEMP,F ; WAIT A WHILE
>* remove GOTO $-1
> BTFSC ADCON0,2 ; TEST FOR END OF CONVERSION
> GOTO $-1
> MOVF ADRES,W ; LOAD A/D RESULT INTO W
> MOVWF CH_1_RESOLT ; STORE IT
>
>
> GOTO MAIN
>
> END
>
Have you considered putting the code to generate the output waveform in
the interrupt handler, but leave the A to D code in the main loop?
A while back, I designed some PIC code for a circuit that went into a
ruggedized portable PC that had internal heating elements. This PC was for
data collection in test aircraft, the PC had to function at -30 deg C. The
PIC had to sample four temp sensors, calculate the required PWM duty
cycles for the five heating elements, and generate the five PWM outputs
that controlled FETs to switch power to the heaters.
I put the A to D code and the calculation code in the main program loop -
real easy stuff there.
The difficult part was the PWM outputs. The heaters consume a huge amount
of power, so all five could not be on at the same time. I had to
synchronize and interleave the PWM outputs to not exceed the power budget
(and burn up the power supply section!) In the interrupt code, I had a
counter that would increment each interrupt. The main loop calculated the
start and end count number for each of the five PWM outputs. The interrupt
turned on/off the appropriate PWM outputs when the count equalled the
start/stop values. Worked great, so I submitted the design.
In testing, the client wanted the PWM frequency increased. But I already
had the TMR0 prescaler at 0, and the PIC was running at 20Mhz. The
interrupt code could not be made smaller, so I decided to modify the TMR0
value from inside the interrupt routine. Since TMR0 caused an interrupt
when it rolls from 0xFF to 0x00, TMR0 has a value of 0 when the interrupt
routine begins. The first instructions in my interrupt routine (except
saving STATUS and W) were to load TMR0 with a new value. This forced the
interrupt frequency to increase.
To get the maximum PWM frequency, the interrupts happened so often that
the main loop code would execute about five instuctions between
interrupts. Any faster and the main loop would never get a chance to run!
So, try putting your output code in the interrupt handler, and if the top
frequency is still inadequate, modify TMR0 in the interrupt handler to
force interrupt frequency to increase. Carefully calculate worse-case
timing and make sure the main loop gets a chance to execute.
Hello - I am looking at using an external zener diode based reference to
input into one of the comparator input pins on the '620 PIC. After an
initial flip though the data sheets I can't find what the "typical" input
impedance is or what the input current (probably very low) is. Perhaps
there is someone that can set me straight on this.
And all that time I was worried about low RDS(on) of the MOSFETs. I could have u
sed
cheaper parts. Design it so MTBF = warranty period.
Actually the motherboard was able to heat itself once temperature rose enough to
turn
on the hard drive and boot up. Wish I could have piped some of that Pentium gene
rated
heat through the hinge to the screen.
Dave
Marc Heuler wrote:
> Hi David (David Sorlien), in <RemoveME3567195E.DCCFEA4FspamBeGonegeocities.com> on May 23 you w
rote:
>
> > synchronize and interleave the PWM outputs to not exceed the power budget
> > (and burn up the power supply section!)
>
> That would have generated enough heat for the computer, wouldn't it :-)
At 08:16 AM 6/7/98 PDT, you wrote:
>Hi everyone, i'm looking for a ADC 10 bit with a SO (Serial Output),
>with a clock that can go up to 10 MHZ... I've looked but i found
>nothing...
>
>Any suggestion???
>
>Thankz for the help!
>Sylvain
I used the TLC2543CN and it seemed quite good and you might be able to
get a high speed version, there's a .PDF file on TI's site some...
Some say there is no magic but, all things begin with thought then it becomes
academic, then some poor slob works out a practical way to implement all that
theory, this is called Engineering - for most people another form of magic.
Sylvain Bilanger wrote:
>
> Hi everyone, i'm looking for a ADC 10 bit with a SO (Serial Output),
> with a clock that can go up to 10 MHZ... I've looked but i found
> nothing...
>
> Any suggestion???
>
> Thankz for the help!
> Sylvain
>
> ______________________________________________________
> Get Your Private, Free Email at http://www.hotmail.com
Hummm
I asked for my friend and he said that Burr Brown or Harris has!
There are lots of parallel high spped/high resolution ADCs from
Burr-Brown. However, I don't think that you will find a serial one which
can run this fast(at least, not yet and/or not cheaply). The highest spped
serial one I have seen was
400Ksamp/sec. The reason is that you are asking for 10 bits @ 10 MHz,
think about that: thats 100Mbits/sec, you are talking something
equivalent to fast eithernet. Actually, to get reliable communications,
you need to pass at least up to the 5th harmonic or so, so you are
talking 500MHz BW on the output drivers of the chip.
Good luck,
Sean
On Mon, 6 Jul 1998, Michael S. Hagberg wrote:
> check out the http://www.maxim-ic.com/efp/ADconv.htm site, they have a wide
> range of devices to choose from.
>
> michael
>
> {Original Message removed}
> I seek a simple means to measure 20 Volt DC with a PIC 16C84. 8 bits
> resolution suffices.
--SNIP--
> Would someone have a schema using a NE555 (or other small IC) in
> voltage/frequency converter whose PIC could have measure the period ?
for a simple 555 setup. You can't measure down to 0V with it, though, but
you might consider another Op-Amp stage which adds, say, 5V to your input
voltage and then gives it to the 555 (it's a good idea to buffer the
input anyway). On the other hand you might run into troubles with
accuracy then.
Why don't you use a cheap A/D converter like the ZN449? I got some
recently for as cheap as 0.95DM here. If that's too many pins (18), use a
shift register with parallel load to serialize the data.
I use a opamp as a comparator to compare a pwm output to the voltage to
be measured (scaled to 1/4 in your case).
The component count is similar to a 555 but uses two pins
it measures to 0V
The circuit and code (in basic) is available to anyone who wants it
I am very interested by your circuit
I want to make 'intelligent' battery switcher / solar charger for my ZAP
electric bicycle.
Can you send me your schemaÊ?
> Hi Peter,
> Thanks for your reply.
>
> I am very interested by your circuit
> I want to make 'intelligent' battery switcher / solar charger for my ZAP
> electric bicycle.
> Can you send me your schema ?
>
> Many thanks in advance
>
> Robert Rivoir
>
>
Thank you for your reply. Our approach is interesting but
I program with MPLAB. It has no integrated 'PWM' function. I have to
program a PWM to control the speed of a DC-Motor by using the 16C84 timer.
It seems me difficult to program two independent PWM in the same PIC without
dummy software loop...
At 11:01 25/09/98 +0200, you wrote:
>I program with MPLAB. It has no integrated 'PWM' function. I have to
>program a PWM to control the speed of a DC-Motor by using the 16C84 timer.
>It seems me difficult to program two independent PWM in the same PIC without
>dummy software loop...
PWM program, with ratio modification on the fly can be found in
UMPSDEMO\EXAMPLES\PIC16C84 directory. It includes also a UMPS project
that allow to verify PWM is runing well.
>David W. Duley wrote:
>
>> I wrote the crack about a wifely reset button! The problem is that if
>> my wife had a reset button there are days that I would just set a big
>> book or somthing on it and then I would watch the Three Stooges
>> marathon on TV.
>
Paul B. added:
> No, my experience (or rather, long-term memory) suggests that a decent
>FDISK every say, 2 years, would reduce the Reset button usage to
>negligible levels.
>--
Hmmmm.... to go a few steps further.... what sort of circumstances would
justify a motherboard replacement? What's our position on dual operating
systems?
> Hmmmm.... to go a few steps further.... what sort of circumstances
> would
> justify a motherboard replacement? What's our position on dual
> operating
> systems?
>
> Reg Neale
>
>
or is this a mother-in-law board replacement?
isn't it nice we all have such a strange sense of humor!
> Hmmmm.... to go a few steps further.... what sort of circumstances would
> justify a motherboard replacement?
You are usually stuck with what genealogy bestowed on you, but you can
change your name ;) But if you're talking computers, the next
advertisement for a better board and a lack of complaints on Dejanews re:
the new product. What has this got to do with fdisk ?
> What's our position on dual operating
> systems?
Sweet side-stepping, where would I be without it, now ;)
In a message dated 9/25/98 6:43:04 AM Pacific Daylight Time, hcooperEraseMEES.COM
writes:
<< >
or is this a mother-in-law board replacement?
isn't it nice we all have such a strange sense of humor!
>>
What sense of humor? I'm living it. Have you ever been married? I would
love to see my mother-in-law's picture on the back of a milk carton! Id like
to send here to visit Jimmy Hoffa......
Slowly I turned..............
> What sense of humor? I'm living it. Have you ever been married? I
> would love to see my mother-in-law's picture on the back of a milk
> carton! Id like to send her to visit Jimmy Hoffa......
Err, this must be parochial humour. What's the significance of the
obverse end of the milk carton and who praytell is Jimmy?
--
Cheers,
Paul B.
FWIW, I've found it easier to make a speedo/RPM meter using
National Semiconductor's LM2907/LM2917 Frequency to Voltage converter.
You can hook up a magnetic pickup directly to the input of the IC
(differential
input) or using conditioning circuits, the negative lead of the coil.
The output is then a voltage that is linearly proportional to the input
frequency. Hook this to the LM3914 10 LED bargraph IC and you are done,
or use scaling resistors and a cheap 3-1/2 digit panel DMM for digital
output.
Don't have to worry about refresh rates, timebases, etc, and easily
calibrated.
At 08:45 1998-10-23 -0700, you wrote:
>FWIW, I've found it easier to make a speedo/RPM meter using
>National Semiconductor's LM2907/LM2917 Frequency to Voltage converter.
>
>You can hook up a magnetic pickup directly to the input of the IC
>(differential
>input) or using conditioning circuits, the negative lead of the coil.
>
>The output is then a voltage that is linearly proportional to the input
>frequency.
If that cirquit use a capacitor for conversion, beware to select one thet
has little temp drift (som cap drifts are huge!)
/Morgan
/ Morgan Olsson, MORGANS REGLERTEKNIK, SE-277 35 KIVIK, SWEDEN \
\ RemoveMEmrtEraseMEspam_OUTiname.com ph +46(0)414 70741 fax +46(0)414 70331 /
I am currently emulating analog to digital conversions with the
PICMASTER on a 17C series part. I have noticed that there is quite a
discrepancy between the emulator reading and a real chip reading. Has
anyone else come across this or is this just one of those days?
John
By the way, the way I tested this was by setting the analog voltage to
3.00V and then spitting out the readings onto 10 LEDS.
>I am currently emulating analog to digital conversions with the
>PICMASTER on a 17C series part. I have noticed that there is quite a
>discrepancy between the emulator reading and a real chip reading. Has
>anyone else come across this or is this just one of those days?
>
>John
>
>By the way, the way I tested this was by setting the analog voltage to
>3.00V and then spitting out the readings onto 10 LEDS.
Yes, I've seen this. For me, it occured when I had the probe head jumpered
to operate from PC power supply instead of target system power supply. When
I changed the jumper to use the target system's power, the a/d readings went
to where they should have been.
Note: this was with a 16c71 probe head. My software configured the a/d to
use VCC as the reference. The picmaster sucked enough current that it's
supply was down to about 4.5V while being powered by the PC. You might also
want to try using the external power supply supplied with the picmaster (I
never did bother since moving the jumper fixed *my* problem).
To Anyone,
After many hours of fingering over my code in search of a couple
of bugs, I have finished a working version of an IR remote control
decoder! The only impediment in my path to complete success is a minute
hardware problem. I am using a PIC16C84 to receive IR commands from a
Kenwood remote. If the PIC receives the correct command it will start,
stop or pause a SONY portable CD player. The CD player is the run of the
mill portable player, which requires the user to depress a button to
begin playing the CD, etc. I want to use the remaining pins on the PIC
to toggle these switches. I tried to pull the terminal from the switch
to ground using the PIC, but got no response. I assume that there is too
much internal resistance through the PIC's PORTB pins to ground for the
switch to activate. Might this be correct? I thought about using a FET
with teh gate connected to the PIC and the high side of the CD player's
swithc connected to the source and the low side connected to drain
(ground). Does anyone have any alternative suggestions that are low
power and low component number?
Aaron Hickman wrote:
<snip> I thought about using a FET
> with teh gate connected to the PIC and the high side of the CD player's
> swithc connected to the source and the low side connected to drain
> (ground). Does anyone have any alternative suggestions that are low
> power and low component number?
I'm not going to be much help for you, Aaron. I will soon need to do something
similar, but have not done it yet. I was going to use a garden-variety 74HCT406
6
Quad Bi-Lateral Switch. It is driven well by TTL-level inputs whereas discrete
parts may not be turned ON all the way by the PIC's output. I have ordered and
received the parts, but alas, they have set on my prototyping bench in their
shipping tube for nearly a month. My best *guess* is that connecting these acro
ss
a switch *ought* to make a closure, but I have not done it yet.
I also would be interested in any ideas of the group. Any pointers to
DIP/SIP-package switches with a lower Ron? Other voices of experience out there
?
Michael
*************************************************************************
When the way of the Tao is forgotten, kindness and ethics must be taught.
Men must learn to pretend to be wise and good. -- Lao Tzu
*************************************************************************
Tell the PICLIST more about the interface to the CD. Are the buttons
on the CD player a machanicla short one side to ground snap dome type.
Or are the buttons in a matrix pettern ike that of a kepad stober machanism.
I would think for mass production the latter. These carry 50K+ Ohms to a
node. The Nodes would need to be determined and understand which pair of
connection (extra wires) you would need to activate an analog switch with a
ballast of the predetermined resistance and perhaps exta series R value to
compensate for the controllers input pins fool current. This could be drive
from a PIC pin.
>To Anyone,
> After many hours of fingering over my code in search of a couple
>of bugs, I have finished a working version of an IR remote control
>decoder! The only impediment in my path to complete success is a minute
>hardware problem. I am using a PIC16C84 to receive IR commands from a
>Kenwood remote. If the PIC receives the correct command it will start,
>stop or pause a SONY portable CD player. The CD player is the run of the
>mill portable player, which requires the user to depress a button to
>begin playing the CD, etc. I want to use the remaining pins on the PIC
>to toggle these switches. I tried to pull the terminal from the switch
>to ground using the PIC, but got no response. I assume that there is too
>much internal resistance through the PIC's PORTB pins to ground for the
>switch to activate. Might this be correct? I thought about using a FET
>with teh gate connected to the PIC and the high side of the CD player's
>swithc connected to the source and the low side connected to drain
>(ground). Does anyone have any alternative suggestions that are low
>power and low component number?
>
>Aaron Hickman
Aaron,
Unconventional as it may sound but..
We ( at the Theatre ) needed to remote select funtions on a CD player, and
ended up using a
BIPOLAR transistor, C-E across the hard switch to ground, Base fed with 1K
I Theenk ) Resistor
(as a current limiter). You may like to try this as a "get you going"
technique, and let us know how
it all pans out.
I did something similar to a Sony CD head unit in my Mazda Protege. I us
ed
the existing steering wheel mounted cruise control buttons to control track
and volume functions on the headunit. Normally the buttons controlled the
normal cruise functions, but if both were pressed at the same time the
function would change. If left alone for more than 2 seconds the function went
back cruise. I too used a direct connection to the miniature snap dome
switches on the facepanel to a pin on a PIC16C54. I had the same problems
you're mentioning. Then I thought about it. The normal voltage on that side of
the switches is floating, not +5v. So instead of just setting the particular
pin after the button was released, I turn it into an input to tristate it.
After that change was made in the software, it worked wonderfully. Good luck.
Matt.
>To Anyone,
> After many hours of fingering over my code in search of a couple {Quote hidden}
>of bugs, I have finished a working version of an IR remote control
>decoder! The only impediment in my path to complete success is a minute
>hardware problem. I am using a PIC16C84 to receive IR commands from a
>Kenwood remote. If the PIC receives the correct command it will start,
>stop or pause a SONY portable CD player. The CD player is the run of the
>mill portable player, which requires the user to depress a button to
>begin playing the CD, etc. I want to use the remaining pins on the PIC
>to toggle these switches. I tried to pull the terminal from the switch
>to ground using the PIC, but got no response. I assume that there is too
>much internal resistance through the PIC's PORTB pins to ground for the
>switch to activate. Might this be correct? I thought about using a FET
>with teh gate connected to the PIC and the high side of the CD player's
>swithc connected to the source and the low side connected to drain
>(ground). Does anyone have any alternative suggestions that are low
>power and low component number?
I did something similar to a Sony CD head unit in my Mazda Protege. I us
ed
the existing steering wheel mounted cruise control buttons to control track
and volume functions on the headunit. Normally the buttons controlled the
normal cruise functions, but if both were pressed at the same time the
function would change. If left alone for more than 2 seconds the function went
back cruise. I too used a direct connection to the miniature snap dome
switches on the facepanel to a pin on a PIC16C54. I had the same problems
you're mentioning. Then I thought about it. The normal voltage on that side of
the switches is floating, not +5v. So instead of just setting the particular
pin after the button was released, I turn it into an input to tristate it.
After that change was made in the software, it worked wonderfully. Good luck.
Matt.
>To Anyone,
> After many hours of fingering over my code in search of a couple {Quote hidden}
>of bugs, I have finished a working version of an IR remote control
>decoder! The only impediment in my path to complete success is a minute
>hardware problem. I am using a PIC16C84 to receive IR commands from a
>Kenwood remote. If the PIC receives the correct command it will start,
>stop or pause a SONY portable CD player. The CD player is the run of the
>mill portable player, which requires the user to depress a button to
>begin playing the CD, etc. I want to use the remaining pins on the PIC
>to toggle these switches. I tried to pull the terminal from the switch
>to ground using the PIC, but got no response. I assume that there is too
>much internal resistance through the PIC's PORTB pins to ground for the
>switch to activate. Might this be correct? I thought about using a FET
>with teh gate connected to the PIC and the high side of the CD player's
>swithc connected to the source and the low side connected to drain
>(ground). Does anyone have any alternative suggestions that are low
>power and low component number?
matt,
good way to emulate a press button switch from a Pic is to interface a
4066 device. Each DIP 14 package contains four switches which can be
directly controlled via the Pic using either spare portB pins or if
these are not available using Peek& Poke on portA Don't forget to hold
the relative pin "high" for a sufficient period of time to mimic a P.B.
switch. Bias the four control lines to ground via 10K.
As each pin is taken high the switch will close.
> The CD player is the run of the mill portable player, which requires
> the user to depress a button to begin playing the CD, etc. I want to
> use the remaining pins on the PIC to toggle these switches. I tried
> to pull the terminal from the switch to ground using the PIC, but got
> no response.
Firstly, did you check exactly what the switch did? Does it actually
pull a wire to ground? Directly to ground?
> I assume that there is too much internal resistance through the PIC's
> PORTB pins to ground for the switch to activate.
In itself, this is absurd; the impedance of a PIC pulling to ground
can be extrapolated from the 1oading curves to be 40mA per volt or 25
ohms. This is much less than a 4066 whose impedance is estimated at 120
ohms.
> Might this be correct?
It *may* be the opposite. Others have mentioned using 4066 switches
to effect switch closures on matrix keypads, but the "discman"-type
players use for remote control, a resistive encoding the same as the
last of the wired-remote VCRs (those with a 2-wire remote) where
different resistors correspond to different commands. The internal
controls, if that is to what you are trying to connect, may do just the
same.
You really will need to research the circuit carefully, and figure out
where both contacts of the switch lead.
> I thought about using a FET with the gate connected to the PIC and
> the high side of the CD player's switch connected to the source and
> the low side connected to drain (ground).
A VN10KM or similar will certainly have even lower "on" resistance,
but I very much doubt that is what you need.
Glenville T. Sawyer wrote:
> We ( at the Theatre ) needed to remote select funtions on a CD
> player, and ended up using a BIPOLAR transistor, C-E across the hard
> switch to ground, Base fed with 1K (I Theenk) Resistor (as a current
> limiter).
Will work where appropriate. Unless you really need low resistance,
47k or so would probably switch it. 1k may actually interfere with
multiplexing. But if you use a FET or 4066, you don't need the bias
resistor!
Matthew Ballinger wrote:
> Then I thought about it. The normal voltage on that side of the
> switches is floating, not +5v. So instead of just setting the
> particular pin after the button was released, I turn it into an input
> to tristate it.
This would also be consistent with the use of resistive encoding, or
at least ternary encoding, which is also common. IOW, to economise on
input pins, the terminal is held at ¸Vcc (by an internal divider) and
comparators sense switch operation pulling it either to Vcc or ground.
Howard Wicking wrote:
> Good way to emulate a press button switch from a Pic is to interface a
> 4066 device. ... Don't forget to hold the relative pin "high" for a
> sufficient period of time to mimic a P.B. switch.
The standard 4066 solution, and a debounce consideration.
--
Cheers,
Paul B.
Maybe try somthing like 4016 / 4066 quad bilateral switch they have gate pin
and 4 switches in one packet useful if u dont know if the switchecs in the CD
player are multiplexed ect.
> which gives 25 ohms Ron at 4.5V.
>
> I also would be interested in any ideas of the group. Any pointers to
> DIP/SIP-package switches with a lower Ron? Other voices of experience
> out there?
imho, the Ron should not be a problem for this application. Micro
miniature switches in consumer equipment often use conductive plastic
and/or rubber switching elements and show up to 470 ohms Ron. It also
depends on how hard you press (I've played with this ;).
If there are serious space constraints a SMT PNP transistor will usually
work here. It is connected between the scan and the read line directly on
the back of the switch (C & E), and a thin wire connects the base to the
external base resistor. This assumes a HIGH driving scan line. A scope is
required to make sense of the signals beforehand. A NPN transistor is
required for LOW driving scan lines. Obtaining a copy of the schematic
diagram helps a lot (easy with Sony).
Also, using a micro miniature connector avoids having to drill holes etc
in the apparatus. In a pinch, a bar of SIPP machined IC sockets can be
epoxied inside the apparatus, female side outwards, after small (0.8 mm)
holes were drilled through the case in a suitable place. The mating
connector is a similar strip of sockets with long pins with a ribbon cable
soldered to the female side of it. Clip off a pin for keying (and don't
drill the corresp. hole).
The base resistor can be as high as 100k, I often use 47k in this
position. If the apparatus controller and the driving controller operate
at different Vdds extra precautions are required to make sure that the
switches turn on and off as required.
imho you can use a 4066 analog switch for all the buttons. It has 4 true
CMOS switches inside. The voltage on the Discman [tm] buttons is usually a
series of pulses in the 0..3V domain. If you connect each 4066 section in
parallel with one of the switches and the GND to the player GND it should
work very well. I've used this method before, with VCRs. Sometimes a 4053
can be used (two scan lines:three sense lines = 6 switches w. one chip).
>I was going to use a garden-variety 74HCT4066
>Quad Bi-Lateral Switch. It is driven well by TTL-level inputs...
> ...which gives 25 ohms Ron at 4.5V.
>Any pointers to DIP/SIP-package switches with a lower Ron?
Michael -
I've never liked the 4066 series, as they have relatively high
on-resistance, though at 25 ohms they seem to have gotten better. My
favorite for 5 Volt operation is the Analog Devices AD51x series. Also
check out Maxim. They're great with samples, though don't expect to
necessarily get production quantities with reasonable lead times. And
Fairchild has single-gate parts available if you only need one or two.
>>I was going to use a garden-variety 74HCT4066
>>Quad Bi-Lateral Switch. It is driven well by TTL-level inputs...
>> ...which gives 25 ohms Ron at 4.5V.
>
>>Any pointers to DIP/SIP-package switches with a lower Ron?
>
Remember you can hook them in parallel - May be cheaper than using
more exotic devices.
> ë˜: Aaron Hickman <.....hickmaabSTOPspam@spam@DREXEL.EDU>
> 攓—: PICLISTEraseME@spam@MITVMA.MIT.EDU
> 񌓈: FET's as analog switch???
> €ˆ˜ˆ: 20 ŠŒˆ‡ÝØ 1998 ‹. 1:26
>
> To Anyone,
> After many hours of fingering over my code in search of a couple
> of bugs, I have finished a working version of an IR remote control
> decoder! The only impediment in my path to complete success is a minute
> hardware problem. I am using a PIC16C84 to receive IR commands from a
> Kenwood remote. If the PIC receives the correct command it will start,
> stop or pause a SONY portable CD player. The CD player is the run of the
> mill portable player, which requires the user to depress a button to
> begin playing the CD, etc. I want to use the remaining pins on the PIC
> to toggle these switches. I tried to pull the terminal from the switch
> to ground using the PIC, but got no response. I assume that there is too
> much internal resistance through the PIC's PORTB pins to ground for the
> switch to activate. Might this be correct? I thought about using a FET
> with teh gate connected to the PIC and the high side of the CD player's
> swithc connected to the source and the low side connected to drain
> (ground). Does anyone have any alternative suggestions that are low
> power and low component number?
>
> Aaron Hickman
>
>
> Hi,
> In like event I used an optical vapour. Works.
> VADIM
> RemoveMEvadspamBeGoneanet.lv
> ----------
> > ë˜: Aaron Hickman <spamBeGonehickmaabKILLspam@spam@DREXEL.EDU>
> > 攓—: PICLISTspam_OUT@spam@MITVMA.MIT.EDU
> > 񌓈: FET's as analog switch???
> > €ˆ˜ˆ: 20 ŠŒˆ‡ÝØ 1998 ‹. 1:26
> >
> > To Anyone,
> > After many hours of fingering over my code in search of a couple
> > of bugs, I have finished a working version of an IR remote control
> > decoder! The only impediment in my path to complete success is a minute
> > hardware problem. I am using a PIC16C84 to receive IR commands from a
> > Kenwood remote. If the PIC receives the correct command it will start,
> > stop or pause a SONY portable CD player. The CD player is the run of the
> > mill portable player, which requires the user to depress a button to
> > begin playing the CD, etc. I want to use the remaining pins on the PIC
> > to toggle these switches. I tried to pull the terminal from the switch
> > to ground using the PIC, but got no response. I assume that there is too
> > much internal resistance through the PIC's PORTB pins to ground for the
> > switch to activate. Might this be correct? I thought about using a FET
> > with teh gate connected to the PIC and the high side of the CD player's
> > swithc connected to the source and the low side connected to drain
> > (ground). Does anyone have any alternative suggestions that are low
> > power and low component number?
> >
> > Aaron Hickman
> >
dialect in russian, I in english nor in the teeth by the leg, when-that
long ago studied german language, so beg pardon for incomprehensible words,
which inserts my SOCRAT97.
Sometimes helps my wife, which nothing does not understand in the
electronics.
on your question:
yes, optoisolator fotodiod->darl works much on the matrix keyboard well,
fall of voltage not more than 0,2 volts and needed the whole one resistor
(in circuits PIC-a diode).
couple
> > of bugs, I have finished a working version of an IR remote control
> > decoder! The only impediment in my path to complete success is a
minute
> > hardware problem. I am using a PIC16C84 to receive IR commands from a
> > Kenwood remote. If the PIC receives the correct command it will start,
> > stop or pause a SONY portable CD player. The CD player is the run of
the
> > mill portable player, which requires the user to depress a button to
> > begin playing the CD, etc. I want to use the remaining pins on the PIC
> > to toggle these switches. I tried to pull the terminal from the switch
> > to ground using the PIC, but got no response. I assume that there is
too
> > much internal resistance through the PIC's PORTB pins to ground for the
> > switch to activate. Might this be correct? I thought about using a
FET
> > with teh gate connected to the PIC and the high side of the CD player's
> > swithc connected to the source and the low side connected to drain
> > (ground). Does anyone have any alternative suggestions that are low
> > power and low component number?
> >
> > Aaron Hickman
> >
----------
Vadim Jakunin wrote:
>
> regard,
>
> dialect in russian, I in english nor in the teeth by the leg, when-that
> long ago studied german language, so beg pardon for incomprehensible words,
If you are not sure, I think you should feel free to write the word /
question
comment also in german. Here are several contributors who can understand
german
as well.
> which inserts my SOCRAT97.
> Sometimes helps my wife, which nothing does not understand in the
> electronics.
>
> on your question:
> yes, optoisolator fotodiod->darl works much on the matrix keyboard well,
> fall of voltage not more than 0,2 volts and needed the whole one resistor
> (in circuits PIC-a diode).
>
I have a small question. It might be stupid, but...
I need to measure a DC current using a probe resistor in a circuit. The
resistor is in the +-branch and at the highest voltage available in the
system. This current needs to be transformed into a ground-referenced
voltage for ADC purposes. I'll try an ASCII schematic:
Assuming R2 == R4 and the differential amplifier gain is Ao = R8/R7, the
expression for the output voltage assumes the form:
Vo = Ao*U1*I1*R1*R5/(R3 + R5)
this is very nice, but I'd like to get rid of U1, for obvious reasons. U1
is not fixed, obviously. The most direct way is, of course, to measure U1
at the same time, and divide Vo by something proportional to U1 (in
software). (U1 IS measured at the same time by other parts of the
circuit).
Question: Is there a cunning way to avoid this, using *simple* analog
circuits to inject a current proportional to U1 into the '-' input of the
op-amp at point A ? I know how to do this with 2 current mirrors and a R.
Any other ideas ? An op-amp voltage controlled current source referenced
to U1 ? Pros and cons ?
Note that the expressions come off a bit of paper, and that it' 9PM here.
There may be errors.
I don't know if this is exactly what you are looking for but I have a
circuit where I measure a 4-20mA DC current through a resistor. I use a
LTC1043 "swinging cap" chip which takes a differential voltage and converts
it to a ground referenced voltage, without op-amps or having to match
resistors or do any conversions. I'm using one on a motor drive card and
have never had any problems with them; they seem solid.
> Hello,
>
> I have a small question. It might be stupid, but...
>
> I need to measure a DC current using a probe resistor in a circuit. The
> resistor is in the +-branch and at the highest voltage available in the
> system. This current needs to be transformed into a ground-referenced
> voltage for ADC purposes. I'll try an ASCII schematic:
>
> R1
> U1, I1 >-----*---/\/\/\---*-----> U1 - R1*I1, I1
> | |
> / /
> R2 \ R3 \
> / /
> \ \
> | | R6 |\
> *------------ ---/\/\/\---------+ \
> | | R7 | >----*----O Vo
> | *---/\/\/\----*----- / |
> | | | |/ |
> / / | R8 |
> R4 \ R5 \ *---/\/\/\---+
> / / ^
> \ \ A
> | |
> === ===
> /// ///
> GND GND
>
> Assuming R2 == R4 and the differential amplifier gain is Ao = R8/R7,
> the expression for the output voltage assumes the form:
> Vo = Ao*U1*I1*R1*R5/(R3 + R5)
> this is very nice, but I'd like to get rid of U1, for obvious reasons.
Well, the first way is to add the missing resistor, R9, which is
supposed to be between the positive input of the Op-amp and ground.
However, the alternative is to remove the assumption that R2/R4 equals
R3/R5, and adjust this ratio to correct for the absence of R9. Whilst
this is the low-count option (but not as low as deleting the redundant
R6 and R7 of course), I must agree that the maths becomes hairy.
Just put R9 where it's supposed to be!
--
Cheers,
Paul B.
> Hello,
>
> I have a small question. It might be stupid, but...
>
> I need to measure a DC current using a probe resistor in a circuit.
> The
> resistor is in the +-branch and at the highest voltage available in
> the
> system. This current needs to be transformed into a ground-referenced
> voltage for ADC purposes.
>
[snip]
unfortunately, i can't take credit for this; it
comes to you courtesy of National Semiconductor.
The JFET is used as a buffer. Id = Is, therefore
the output voltage reflects the current draw. The
circuit shows R1 = 0.1, R2 = 100, R3 = 5K. That
gives 5V/A output.
Peter L. Peres wrote:
>
> I have a small question. It might be stupid, but...
>
> I need to measure a DC current using a probe resistor in a circuit. The
> resistor is in the +-branch and at the highest voltage available in the
> system. This current needs to be transformed into a ground-referenced
> voltage for ADC purposes. I'll try an ASCII schematic:
Then Vo = Vrs * (R2/R1) where Vrs is the voltage drop across Rs.
The voltage drop across Rs is Vrs = I * Rs
-------------------------------------------------------------------------------
Mike mwestfal@spam@odc.net http://web.csusb.edu/public/csci/mwestfal
Linux religious dogma: "The Gates of Hell shall not prevail."
-------------------------------------------------------------------------------
Well, not being an analog sort of guy, I probably would have taken an
"analog computer" approach - negate U1-R1*I1, add to U1 (gives R1*I1),
multiply by appropriate scale factor. Three opamps (still one
package!), if you're dumb. I'm pretty sure it'd condense down to one
if you're clever; probably look a lot like the circuit you posted, too...
RX is the current probe resistor.
R1=R3
R2=R4
Gain=R1/R2
Vout=(I*Rx)*Gain
U1 is no longer a term.
This configuration is a simple differential amplifier circuit.
It may not be the optimal circuit, but it will work.
The resistors R1 R2 R3 R4 must be precision resistors.
R2 must be at least 100 times larger than Rx for accuracy.
There are precision differential instrumentation amps
available from companies like Burr Brown and others that
incorporate an improved version of the above in a single package.
> From: Peter L. Peres <EraseMEplpRemoveMESTOPspamACTCOM.CO.IL>
> To: RemoveMEPICLISTKILLspamTakeThisOuTMITVMA.MIT.EDU
> Subject: [OT]: Analog (opamp) question
> Date: Thursday, January 07, 1999 4:25 PM
>
> Hello,
>
> I have a small question. It might be stupid, but...
>
> I need to measure a DC current using a probe resistor in a circuit. The
> resistor is in the +-branch and at the highest voltage available in the
> system. This current needs to be transformed into a ground-referenced
> voltage for ADC purposes. I'll try an ASCII schematic:
>
> R1
> U1, I1 >-----*---/\/\/\---*-----> U1 - R1*I1, I1
> | |
> / /
> R2 \ R3 \
> / /
> \ \
> | | R6 |\
> *------------ ---/\/\/\---------+ \
> | | R7 | >----*----O Vo
> | *---/\/\/\----*----- / |
> | | | |/ |
> / / | R8 |
> R4 \ R5 \ *---/\/\/\---+
> / / ^
> \ \ A
> | |
> === ===
> /// ///
> GND GND
>
>
> Assuming R2 == R4 and the differential amplifier gain is Ao = R8/R7, the
> expression for the output voltage assumes the form:
>
>
> Vo = Ao*U1*I1*R1*R5/(R3 + R5)
>
>
> this is very nice, but I'd like to get rid of U1, for obvious reasons. U1
> is not fixed, obviously. The most direct way is, of course, to measure U1
> at the same time, and divide Vo by something proportional to U1 (in
> software). (U1 IS measured at the same time by other parts of the
> circuit).
>
> Question: Is there a cunning way to avoid this, using *simple* analog
> circuits to inject a current proportional to U1 into the '-' input of the
> op-amp at point A ? I know how to do this with 2 current mirrors and a R.
> Any other ideas ? An op-amp voltage controlled current source referenced
> to U1 ? Pros and cons ?
>
> Note that the expressions come off a bit of paper, and that it' 9PM here.
> There may be errors.
>
> tia,
>
> Peter
use an opamp which goes up to the positive rail with its output. short r3 and
r6 and take r5 out. set r2=r7 and r4=r8.
Ao=r8/r7=r4/r2
Vo= i1 * r1 * Ao
you can make the opamp to output current, but i thought you want to measure
current and output voltage...
ge
At 21:25 01/07/99 +0000, Peter L. Peres wrote:
>Hello,
>
> I have a small question. It might be stupid, but...
>
> I need to measure a DC current using a probe resistor in a circuit. The
>resistor is in the +-branch and at the highest voltage available in the
>system. This current needs to be transformed into a ground-referenced
>voltage for ADC purposes. I'll try an ASCII schematic:
> Assuming R2 == R4 and the differential amplifier gain is Ao = R8/R7, the
>expression for the output voltage assumes the form:
>
>
>Vo = Ao*U1*I1*R1*R5/(R3 + R5)
>
>
>this is very nice, but I'd like to get rid of U1, for obvious reasons. U1
>is not fixed, obviously. The most direct way is, of course, to measure U1
>at the same time, and divide Vo by something proportional to U1 (in
>software). (U1 IS measured at the same time by other parts of the
>circuit).
>
>Question: Is there a cunning way to avoid this, using *simple* analog
>circuits to inject a current proportional to U1 into the '-' input of the
>op-amp at point A ? I know how to do this with 2 current mirrors and a R.
>Any other ideas ? An op-amp voltage controlled current source referenced
>to U1 ? Pros and cons ?
>
>Note that the expressions come off a bit of paper, and that it' 9PM here.
>There may be errors.
>
>tia,
>
> Peter
> I need to measure a DC current using a probe resistor in a circuit.
>The
>resistor is in the +-branch and at the highest voltage available in
>the
>system. This current needs to be transformed into a ground-referenced
>voltage for ADC purposes.
Here's a simple circuit commonly used for that purpose:
The +,- and O at the bottom is an op-amp. It is necessary of course that
R1/R2 = R3/R4 in order to reject changes in the supply voltage. Voltage
dropped across Rs is amplified by a gain of R4/R3. If the supply voltage
is rather high, it is hard to keep the op-amp inputs within their range
and also have good gain. This circuit is not optimal in that case.
I'm not sure what your circuit is supposed to do but it looks
unnecesarily complicated. Of course the conventional 2 and 3-amplifier
"instrumentation amplifier" circuits can also be used, offering somewhat
higher performance.
It is sometimes possible to rearrange the circuit so your ADC's ground is
one end of the resistor. This simplifies the current measurement a lot.
___________________________________________________________________
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The circuit looks like it SHOULD do what you want pretty much as is.
Your formula looks approximately correct but is, fortunately, wrong
for a properly designed circuit :-)
Essentially, when the dividers are balanced the required "current
proportional to U1" is effectively provided.
Rather than re-derive I'll say what I think should be done and allow
others to pull out bits of paper and point out why I'm wrong :-).
For R2=R4 as you specified, if you also set R3=R5 (and best R3=R2)
then the amplifier circuit proper is fed by a difference signal of
I1*R1*(R2/R2+R4) = 1/2 * the voltage drop across R1.
The only reason for the dividers here is to limit the maximum input
voltage to keep it inside the common mode range of the op-amp. If the
+ supply of the op-amp is at voltage U1 (which it may not be) then
some opamps will allow a common mode range which includes their
positive supply and the dividers would not be needed. The division
ration does not have to be half as it is here - you can choose any
convenient ratio - it should however be as high as possible as it is
dividing down the 'desired" signal as well as the unwanted power
supply voltage. Use as low a division ratio as your opamps common
mode voltage will allow.
[Common mode voltage (Vcm) is the maximum voltage "common" to both
differential inputs which will be rejected by the op-amp while it
amplifies the difference between them. Vcm is usually expressed both
in absolute terms and usually more importantly, relative to the power
supply voltage in use at the time. There are both positive and
negative Vcm limits and they are often not symmetrical but here only
the positive limit is of concern]
As shown the circuit should work if the dividers R2/R4 and R3/R5 are
balanced.
However, the op-amp input /leakage currents will see different
resistances and produce an offset. This may be overcome by making R6
= to a value of (R8 in parallel with R7). As R8 is probably >> R7
this means R6 will be approximately equal to R7.
Another error source is that the impedance of the dividers will
appear to be part of R6 and R7 - as long as R6 and R7 are >> R2 etc
the problem will be minimised. If not, you can calculate the
equivalent resistance and use it in your figuring. ie add (R3//R5
// = in parallel with) ) to R7 and R2//R4 to R6.
To "completely" overcome the affects of R2 etc unity gain buffers
(opamps with inverting connected to output, input to non-inverting
input) may be placed before R6 and R7.
Approximately:
Vo = R1*I1 * R5/(R#+R5) * R8/Rx
where Rx = R7 + R5//R3
for R2/R4 = R3/R5
and R6~ R7//R8 (ideally? R6+R2//R4 = (R7+R3//R5)//R8 but this
is probably unnecessary)
> I need to measure a DC current using a probe resistor in a
circuit. The
>resistor is in the +-branch and at the highest voltage available in
the
>system. This current needs to be transformed into a
ground-referenced {Quote hidden}
R8/R7, the
>expression for the output voltage assumes the form:
>
>
>Vo = Ao*U1*I1*R1*R5/(R3 + R5)
>
>
>this is very nice, but I'd like to get rid of U1, for obvious
reasons. U1
>is not fixed, obviously. The most direct way is, of course, to
measure U1
>at the same time, and divide Vo by something proportional to U1 (in
>software). (U1 IS measured at the same time by other parts of the
>circuit).
>
>Question: Is there a cunning way to avoid this, using *simple*
analog
>circuits to inject a current proportional to U1 into the '-' input
of the
>op-amp at point A ? I know how to do this with 2 current mirrors and
a R.
>Any other ideas ? An op-amp voltage controlled current source
referenced
>to U1 ? Pros and cons ?
> I need to measure a DC current using a probe resistor in a circuit. The
>resistor is in the +-branch and at the highest voltage available in the
>system. This current needs to be transformed into a ground-referenced
>voltage for ADC purposes. I'll try an ASCII schematic:
circuit and good answers from Paul and Phil snipped.
couple of things: what voltage is your rail? The LT 1490 has an input
stage that goes up to 44V, even with a 3V or 5V rail. Neat device! One of
LT's ap notes shows a high side current sensor doing just what you want.
If you use Phil's suggestion, make sure that you use an op-amp that includes
VCC within the common mode range. This can be one of the LT devices like
above or most JFET op-amps such as the TL071 series.
If you want to stay with a differential amplifier, you could look at some of
the integrated solutions from Burr-Brown or Analog Devices. Their claim to
fame is the very accurately matched resistors within the device. You would
still be left with matching 2 external resistors (the input resistors)
depending upon the voltage of that rail.
Finally, there are a couple of people making high side current sensors with
the shunt integrated right in the package. These work in a fashion similar
to Phil's suggestion. Again, depends on the voltage on that rail. I've
seen at least 2 different approaches but don't have the names of the
manufacturers handy right now. I can look them up if needed.
> Finally, there are a couple of people making high side current sensors with
> the shunt integrated right in the package. These work in a fashion similar
> to Phil's suggestion. Again, depends on the voltage on that rail. I've
> seen at least 2 different approaches but don't have the names of the
> manufacturers handy right now. I can look them up if needed.
These current sense IC's have a 4 milliohm shunt resistor integrated in
the package. The output is a PWM signal. I've never used them, but they
look neat.
Peter, others have mentioned some good circuits. If you want an
integrated solution, take a look at the MAX471/472. These are
high-side current sensors in an 8-pin DIP or SO package. The supply
voltage ranges from 3-36V, they draw 100ua, and have a 2% accuracy.
They provide a voltage output as well as sign/direction. The 471 has an
internal sense resistor and will measure up to 3A (1V/A). The 472 uses
an external resistor. They are intended for use in battery chargers.
- Tom
At 09:25 PM 1/7/99 +0000, Peter L. Peres wrote: {Quote hidden}
>Hello,
>
> I have a small question. It might be stupid, but...
>
> I need to measure a DC current using a probe resistor in a circuit. The
>resistor is in the +-branch and at the highest voltage available in the
>system. This current needs to be transformed into a ground-referenced
>voltage for ADC purposes. I'll try an ASCII schematic:
>
> R1
>U1, I1 >-----*---/\/\/\---*-----> U1 - R1*I1, I1
> | |
> / /
> R2 \ R3 \
> / /
> \ \
> | | R6 |\
> *------------ ---/\/\/\---------+ \
> | | R7 | >----*----O Vo
> | *---/\/\/\----*----- / |
> | | | |/ |
> / / | R8 |
> R4 \ R5 \ *---/\/\/\---+
> / / ^
> \ \ A
> | |
> === ===
> /// ///
> GND GND
>
>
> Assuming R2 == R4 and the differential amplifier gain is Ao = R8/R7, the
>expression for the output voltage assumes the form:
>
>
>Vo = Ao*U1*I1*R1*R5/(R3 + R5)
>
>
>this is very nice, but I'd like to get rid of U1, for obvious reasons. U1
>is not fixed, obviously. The most direct way is, of course, to measure U1
>at the same time, and divide Vo by something proportional to U1 (in
>software). (U1 IS measured at the same time by other parts of the
>circuit).
>
>Question: Is there a cunning way to avoid this, using *simple* analog
>circuits to inject a current proportional to U1 into the '-' input of the
>op-amp at point A ? I know how to do this with 2 current mirrors and a R.
>Any other ideas ? An op-amp voltage controlled current source referenced
>to U1 ? Pros and cons ?
>
>Note that the expressions come off a bit of paper, and that it' 9PM here.
>There may be errors.
>
>tia,
>
> Peter
>
>
> I don't know if this is exactly what you are looking for but I have a
> circuit where I measure a 4-20mA DC current through a resistor. I use a
> LTC1043 "swinging cap" chip which takes a differential voltage and converts
> it to a ground referenced voltage, without op-amps or having to match
> resistors or do any conversions. I'm using one on a motor drive card and
> have never had any problems with them; they seem solid.
Thank you, Ryan,
I have never used a LTC1043, but I am familiar with the principle, and
have used the reed relay based version of the same circuit before ;). How
much common mode voltage will a LTC1043 take, and is it linear (pun ;) ?
I'd like it to be 0.5 % or better when U1 varies over a 2:1 range. This is
easy with op-amps only, and so-so with discrete current mirrors. The large
amount of resistors is not a problem, I will use an 6-fold SIPP for the
matched ones. My gain is x20 and I only need the gain setting resistor
with the SIPP and the probe resistor.
My problem is, that I have to use an inexpensive op-amp (whose other
sections are used for something else) and that I'd want instant response
on this signal (w/o calculation overhead).
I'd like to thank you all for the valuable input on this, I am very
grateful for your help.
The National schematic contributed by Phil Eisermann is very much along
the lines of my 'small cunning analog circuit addition' ;) Unfortunately,
it requires an opamp that allows U1 in its CMMR (U1 is actually higher
than my opamp supply at certain times). It also requires a P-FET and that
I don't have for this project.
Mike Westfall was first to contribute the simple 'direct' solution, of
course, of which I was aware. I started adding complications because of U1
being higher that the opamp CMMR voltage. This is how I got stuck.
I will use a Zener diode as shown in the circuit to prevent this. One
free 'gift' I get is, that the gain is now sub-unitary due to the cmrr
limit vs. U1. Sigh.
I prefer the HI-200 (or DG-200) series for analog switches. Easier to use,
lower on resistance, and a wide variety of styles (DPST, SPST, 4-1 analog mux,
etc)
Actually, that's not quite what I was asking. I do need to use a couple
pins as analog in (for the ADC). But I was wondering if it was possible
to use pins actually set as analog pins in ADCON1 as digital out by
clearing the appropriate tris bits.
Guess it's not possible according to previous posting.
> In message <spam_OUTPine.GSO.4.03.9903070524010.14589-100000spam_OUTspam_OUTmosquito.occ.uc.edu>
> >, Vincent Deno <denovjspam_OUTEMAIL.UC.EDU> writes
> >Has anyone encountered problems using pins assigned as analog in (via
> >ADCON1) as digital out (set in TRIS register)? I realize these pins
>
> Setting three bits in ADCON1 to 11X configures porta and porte as
> digital I/O. Then use TRIS to set direction.
>
> I also need every I/O I can and use porte and porta at times.
>
> Try it
>
>
> --
> Ron Dickinson
>
> Compusolve Business Systems
> 22 Crown Street, Clowne, Chesterfield, Derbyshire S43 4DN, England
> Tel & Fax : 01246 - 570281
>
>On Sun, Mar 07, 1999 at 05:29:27AM -0500, Vincent Deno wrote:
>> Has anyone encountered problems using pins assigned as analog in (via
>> ADCON1) as digital out (set in TRIS register)? I realize these pins
>
>It won't work. If you configure a pin as an analog input, then clearing
>the corresponding TRIS bit will make it useless for analog, but will
>not make it into an output pin.
Sorry to have to disagree, Clyde. Clearing the analog TRIS pins DOES turn
them into outputs. But you cannot use any Read-Modify-Write instructions
with port A since those pins always read as 0.
Perhaps I should clarify things a bit: one of my products uses only 2 a/d
inputs on a 16c73. ADC_CONFIG is 00000100 which sets ra 0,1,2 to a/d inputs
and the rest as digital i/o. Ra3 is usable as output only (not input) and
is always cleared if I perform any R-M-W operation on port A. I have
numerous warnings scattered thru that code to remind me of this so that it
doesn't bite me (again).
I can't speak of any other parts - I haven't had to find out. But pin RA3
is definitely usable as a digital output on a '73 even though it is also
configured as analog input.
> Sorry to have to disagree, Clyde. Clearing the analog TRIS pins DOES turn
> them into outputs. But you cannot use any Read-Modify-Write instructions
> with port A since those pins always read as 0.
...
> I can't speak of any other parts - I haven't had to find out. But pin RA3
Ok, maybe I should clarify that - my tests that determined the above were done
on a 16C71. Maybe the 16C73 and 16C74 are different, but I checked the datasheet
s
for both the '71 and '74 before posting my message, and the wording about
the analog inputs is the same. Furthermore I probably didn't test RA3.
So we may be both right; and the '74 could be different again :-) Personally
I wouldn't rely on it.
At 15:04 03/08/99 +1000, Clyde Smith-Stubbs wrote:
>Ok, maybe I should clarify that - my tests that determined the above were done
>on a 16C71. Maybe the 16C73 and 16C74 are different, but I checked the
>datasheets
>for both the '71 and '74 before posting my message, and the wording about
>the analog inputs is the same. Furthermore I probably didn't test RA3.
now here i'd just like to clarify my understanding of the english language
(even though i agree with you on that i'd probably not rely on it :)
in my data sheets of all the 16c7x series it says "the trisa register
controls the direction of the ra pins, even when they are being used as
analog inputs" in the porta chapter, and "the port pins that are desired as
analog inputs must have their corresponding tris bits set. if the tris bit
is cleared, the digital output level (Voh or Vol) will be converted" in the
adc chapter.
i read this as that the output level will actually be a digital one (Voh or
Vol) in case the tris bit is cleared (which is consistent with the
schematic of the porta inputs in the data sheets). do you read something
different here?
On Mon, Mar 08, 1999 at 12:14:22AM -0800, Gerhard Fiedler wrote:
> in my data sheets of all the 16c7x series it says "the trisa register
> controls the direction of the ra pins, even when they are being used as
> analog inputs" in the porta chapter, and "the port pins that are desired as
> analog inputs must have their corresponding tris bits set. if the tris bit
> is cleared, the digital output level (Voh or Vol) will be converted" in the
> adc chapter.
>
> i read this as that the output level will actually be a digital one (Voh or
> Vol) in case the tris bit is cleared (which is consistent with the
> schematic of the porta inputs in the data sheets). do you read something
> different here?
Well, at no point does it actually say that if the TRIS bit is cleared will
the digital output level appear on the pin; the statement about "the output
level will be converted" means that the analog input will see the digital output
,
but says nothing about what will appear on the external pin.
Certainly nothing in the text is a clear assurance that with TRIS cleared the
pin will work as an output, OTOH I agree with you that the logic diagram does se
em
quite clear; but I know that in practice, I found it not to work. Also remember
that the logic diagram is illustrative only, and is not the actual circuit.
If I get time, I'll run some tests again, just to get to the bottom of this.
I've not followed all the messages in this thread, but I have used
analog in pins as outputs. There are several caveats.
1) Any read-modify-write instructions on any pin on that port will
change your pin to a 0.
2) Any read of the pin or port will show the pin as a 0.
3) All writes must be to the entire port(see #1).
|Has anyone encountered problems using pins assigned as analog in (via
|ADCON1) as digital out (set in TRIS register)? I realize these pins
|wouldn't function properly in digital in mode but that is of no
|consequence, they're always used as output.
As far as I can tell, the ADCON register has two effects:
[1] It enables or disables the ADC. If _ANY_ port pin is selected to
be an analog input, then the ADC can read all of them.
[2] It disables the digital input registers on the pins configured as
"analog". This eliminates the extra current consumption that could
result from having a CMOS input biased at half-rail.
Note that pins may be used for analog input, even when configured as
digital, provided that the ADC is turned on. Current consumption will
be increased somewhat, and digital reads of the port may cause some
small capacitive transients to be coupled to the pin, but otherwise
there shouldn't be any real problems.
As for configuring the pins as analog and then using them for digital
outputs, that works fine provided that you don't use any read/modify/
write operations on the port. If you use a "shadow register" and copy
that to the real port when it's changed, you should do fine.
Again, thanks for everyone's responses and recommendations. For my
application, I will be safe in using the "analog" pins as output because I
will always know the correct state of the pins used as output and will not
need to use any read/modify/write operations.
Regards,
Vincent Deno
PS. Am I the only one who can't read their own posting consistantly?
> |Has anyone encountered problems using pins assigned as analog in (via
> |ADCON1) as digital out (set in TRIS register)? I realize these pins
> |wouldn't function properly in digital in mode but that is of no
> |consequence, they're always used as output.
>
> As far as I can tell, the ADCON register has two effects:
>
> [1] It enables or disables the ADC. If _ANY_ port pin is selected to
> be an analog input, then the ADC can read all of them.
>
> [2] It disables the digital input registers on the pins configured as
> "analog". This eliminates the extra current consumption that could
> result from having a CMOS input biased at half-rail.
>
> Note that pins may be used for analog input, even when configured as
> digital, provided that the ADC is turned on. Current consumption will
> be increased somewhat, and digital reads of the port may cause some
> small capacitive transients to be coupled to the pin, but otherwise
> there shouldn't be any real problems.
>
> As for configuring the pins as analog and then using them for digital
> outputs, that works fine provided that you don't use any read/modify/
> write operations on the port. If you use a "shadow register" and copy
> that to the real port when it's changed, you should do fine.
>
Does anyone have a schematic of an analog to digital converter
that uses only one digital input of a PIC microcontroler?
That's the kind of A/D converter that is used on the joystick
interface of a PC (charging and discharging a capacitor and
measuring the charge or discharge time).
I have a 16C77A based monitoring system that utilizes the analog input
channels. 4 of the channels are connected to temperature sensing devices
that operate on 12 VDC and generate a 1-5 volt analog signal for 32-100
degrees.
When the temperature sensing devices are connected with power on,
occaisionally the processor locks up. We're seeing a 7 volt spike
occaisonally when the devices are plugged in, but no postive proof that
this is locking the processor up.
The watchdog timer is enabled and should reset the processor as the
routines that kick the dog do not appear to be working (reception of serial
input data or timer interrupts). The unit does not respond to the host,
indicating that the serial i/f is not working and an activity LED no longer
flashes, possibly indicating that the PIC is no longer processing
interrupts or is out in left field.
Can an overvoltage condition on the analog input cause the processor to
head for left field?
> I have a 16C77A based monitoring system that utilizes the analog input
> channels. 4 of the channels are connected to temperature sensing devices
> that operate on 12 VDC and generate a 1-5 volt analog signal for 32-100
> degrees.
>
> When the temperature sensing devices are connected with power on,
> occaisionally the processor locks up. We're seeing a 7 volt spike
> occaisonally when the devices are plugged in, but no postive proof that
> this is locking the processor up.
>
> The watchdog timer is enabled and should reset the processor as the
> routines that kick the dog do not appear to be working (reception of serial
> input data or timer interrupts). The unit does not respond to the host,
> indicating that the serial i/f is not working and an activity LED no longer
> flashes, possibly indicating that the PIC is no longer processing
> interrupts or is out in left field.
>
> Can an overvoltage condition on the analog input cause the processor to
> head for left field?
>
> Howard
> Howard McGinnis
> @spam@hmcginniSTOPspam@spam@digital.net
> Electronic Visions, Inc.
> 1650 Barrett Drive
> Rockledge FL 32955
> (407) 632-7530
> http://ddi.digital.net/~hmcginni
> mcginnisspamBeGonespamBeGonee-visions.com
--
Rick Farmer | 916 E. Ogden Ave. #312
Electrical Engineer | Milwaukee, Wi. 53202 spamBeGonerfarmerexecpc.com | 414-273-9740
>Can an overvoltage condition on the analog input cause the processor
>to
>head for left field?
Yes it sure can. It is possible to get into states that WDT or even MCLR
can't recover from. At the very least, connect a resistor in series from
the external wiring to the PIC inputs. Microchip recommends driving the
analog inputs with an impedance of 10K or less, so the resistor should be
10K or less. Digital inputs can use larger resistors, though very large
ones will slow down the response time. The resistor will limit the
current that flows into the PIC pin when the input voltage is excessive.
A simple series resistor is probably enough to deal with your situation.
More complicated protection networks can give better protection when the
overvoltages are high. The more complicated network is typically a "T"
with 2 resistors in series with the signal path and some sort of voltage
clamping device from the center of the T to ground.
Resetting the WDT during a timer interrupt doesn't use it to maximum
advantage. It is quite possible for the main program to get lost but the
interrupts continue to function.
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ok, I figure that I have posted a few good things, so once again, I am
asking the collective to see what they know.
Probably reply by private mail tho.
I'm looking for a PC/104 form analog output card, but must be 4-20mA
outputs. I need 16 channels, so I assume that I will need several cards
(the old STD bus system had 4). I've found a PC/104 to ISA interface card,
so even if I can find at least a 8 channel output card in the ISA form
factor, that would work. I've looked thru the firms listed on http://www.pc104.com, but have also found other companies not listed there (so I am
hoping someone knows of a card that will work for me).
Having a limitation with clerical tasks, I ran into a problem with analog
electronics in college... there was just too damned much math in it, ...
I burned out. (other personal factors didn't help... divorce, kids being
taken away etc....)
Anyway, problem is, I burned out before I got to understanding active
analog circuits very well. Now I have a function I want to play with,
that might be more efficient as an analog circuit....
I suspect I need at least 3 opamps... two unity gain, with both positive
and negative bias and one variable gain... of course I am not sure how to
rig them as multipliers.... etc.
It involves floating point multiplication so its probably too expensive
timewise for a PIC.
So... Assuming I could regulate factors such as powerline voltage, and
temperature fine enough to approximate accuracy....
An analog circuit MIGHT be more to the point.
I would want to supply some sort of 8 bit DAC inputs, and read an ADC
output.
I haven't tried this yet with a PIC, so what I want to know, is....
How long does it take to:
1. Supply an 8 bit DAC value ( I would need two) (PIC?)
2. Stabilize a relatively simple analog circuit to a particular value
after input. ( a variable gain multiplier ) Actual formula is proprietary
figuring out how best to generate the gain, is probably beyond me right now but
I can learn how if it is worth it.
3. read the analog value out using an ADC (PIC?)
in comparison how long would it take to:
lookup a 16 bit Float,and an 8 bit number using an 8 bit value as index
(Its an orthoganol function so I only need to store 128 values for each)
768 bytes total? seems steep for a PIC!
Subtract the lookup from the second value
do a 16 bit floating multiply to
an 8 bit number that was the result of the previous subtraction
add a range adjustment check it fits within the range using another lookup
or two from the same table as the value subtracted came from
getting the result, an 8 bit integer
I marked this OT, because I suspect that I am not going to be able to use
a PIC for this. (too slow for one thing) However, if it works out that I
can build a parrallel processor that does these things in a pipeline like
fashion, maybe the actual PIC timing would become minimized as a factor.
The application I envision for it is an accelerator function, for a large
data array calculation similar to a neural network If I can offload some
of the math to a peripheral accelerator circuit, it might speed the
base application, or allow me to use this function in smaller circuits.
I am on welfare... so COST is DEFINITELY a factor.... which is why I will
probably end up building this circuit myself... some year....
>Anyway, problem is, I burned out before I got to understanding active
>analog circuits very well. Now I have a function I want to play with,
>that might be more efficient as an analog circuit...
The approach you suggest is not practical. It is difficult to get any
analog circuit to work to more than 12 bits or so of precision. A
circuit that multiplies two variable voltages together cannot be realized
with just op-amps (unless tricks are used). Analog multiplier ICs are
made but they are kind of specialized and expensive and introduce several
more types of error. So you're far, far ahead to do the math in
software.
>It involves floating point multiplication so its probably too
>expensive
>timewise for a PIC.
A PIC should be able to do this type of operation about 1000 times per
second with nothing too specialized. The figure of 1000 evaluations per
second is based on running the PIC at 20 MHz; there are 5000 instructions
to do each evaluation. (As an aside, making the analog version work much
faster than a few KHz will significantly complicate it). If higher
speeds are needed then consider a microcontroller with multiply hardware
built in. Most of the PIC 17CXXX's have this, as well as a more
effective way to place tables of data in the program EPROM. But they are
also rather expensive and quirky so you may want to consider a different
brand of processor. The various DSP chips are highly optimized for
multiplying 16 or 32 bit numbers quickly.
If you provide some more details of the formula and the size of numbers
to be used, some of the list's numerical experts could probably suggest
ways to optimize the computation. My first advice would be at least for
now to forget about floating point. It is very rarely necessary in
microcontroller applications since the range of values at each step in
the process can be determined beforehand. Use binary integers that are
scaled so the formula works properly for all possible inputs.
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> On Sun, 13 Jun 1999 13:59:14 -0600 Graeme Smith
> <grysmithRemoveMEFREENET.EDMONTON.AB.CA> writes:
>
> >Anyway, problem is, I burned out before I got to understanding active
> >analog circuits very well. Now I have a function I want to play with,
> >that might be more efficient as an analog circuit...
>
> The approach you suggest is not practical. It is difficult to get any
> analog circuit to work to more than 12 bits or so of precision. A
> circuit that multiplies two variable voltages together cannot be realized
> with just op-amps (unless tricks are used).
Actually I need to input a 16bit value, and output an 8 bit value, so the
precision is less than 12 bits. The problem is, that the circuit I need,
is characterized as a slope type formula... ie: y=mx+b, M tends to
have relatively small changes between different versions, so to get the
same result, in an integer I would have to go to a formula with both
multiplication and division in it. I was hoping to optimize to an easier
form. (hence the variable gain).
Analog multiplier ICs are
> made but they are kind of specialized and expensive and introduce several
> more types of error. So you're far, far ahead to do the math in
> software.
Ok, I suppose that that was part of what I was asking....
>
> >It involves floating point multiplication so its probably too
> >expensive
> >timewise for a PIC.
>
> A PIC should be able to do this type of operation about 1000 times per
> second with nothing too specialized. The figure of 1000 evaluations per
> second is based on running the PIC at 20 MHz; there are 5000 instructions
> to do each evaluation. (As an aside, making the analog version work much
> faster than a few KHz will significantly complicate it).
well that is why I asked, I have no idea what the response rate of an
active circuit should be in the linear range. Remember however this is
part of an accellerator circuit, and will be used for massive data arrays,
so I expect that even a thousand slopes a second, will tend to drag a bit
;)
If higher
> speeds are needed then consider a microcontroller with multiply hardware
> built in. Most of the PIC 17CXXX's have this, as well as a more
> effective way to place tables of data in the program EPROM. But they are
> also rather expensive and quirky so you may want to consider a different
> brand of processor. The various DSP chips are highly optimized for
> multiplying 16 or 32 bit numbers quickly.
I have a 17XX sample or two to work with, so I'll keep this application in
mind when I start trying to familiarize myself with them.
>
>
> If you provide some more details of the formula and the size of numbers
> to be used, some of the list's numerical experts could probably suggest
> ways to optimize the computation.
The values range from 1 to 128 for the 8 bit values (xmin), and
1.0 to 255.0 for the 16 bit values.
There are 63 values between 1.0 and 2.0, for M, of which 1.6XXX has the
most
subvalues, at about 5. I might be able to reduce the accuracy to 2 or 3
sig digits after the point.... but I will have to experiment with that,
and I am not sure I know how to evaluate the effect on my output. After
all I want a smooth function, without too much jitter to it.
Essentially what I need to do, is calculate the Y for a slope function
with a variable slope, and upper and lower limits.
Y = M * (X-Xmin) + -127
is the basic formula.... Simple math.
M is the 16 bit Float, it takes the place of the variable gain. Xmin is
what we lookup for each entry of M ( by index) X falls within the -127 to
128 range. I can reduce the storage for the 255 M values, and Xmin values
because of the particular formula involved to 1/2 of its normal value, but
that will require some fiddling with the index.
either I need to do hardware multiplication, or I need a full 32K-64K
lookup table. I can get by with a 32k one, if I can harness the
orthoganality of the formula at the two byte input level.
If I used a 32K serial eprom lookup, how long would it take to look up the
third value from the table... Assume a 256 X 128 table and two 8 bit
values as indexes.
This might be the most cost effective form of accellerator, but I hesitate
to dump 64k of constants into an eprom unless I know that I need to.
My first advice would be at least for
> now to forget about floating point. It is very rarely necessary in
> microcontroller applications since the range of values at each step in
> the process can be determined beforehand. Use binary integers that are
> scaled so the formula works properly for all possible inputs.
>
Harder to do than it might look.... I am still fighting with the metaphor
I am trying to achieve.... It's hard enough to see the metaphor in the
math right now.... This formula is easy to test, but it lacks the
sophistication I was hoping for.
>
Anyway... Thanks for your evaluation of Analog circuit limitations
I had a similar problem but the equation went from linear to some complex
function. I used the floating point co processor from Al Williams - worked
a treat.
>GRAEME SMITH email: EraseMEgrysmithSTOPspamRemoveMEfreenet.edmonton.ab.ca
>YMCA Edmonton
>
>Address has changed with little warning!
>(I moved across the hall! :) )
>
>Email will remain constant... at least for now.
>
>
>On Sun, 13 Jun 1999, Mike Keitz wrote:
>
>> On Sun, 13 Jun 1999 13:59:14 -0600 Graeme Smith
>> <spam_OUTgrysmithRemoveMEEraseMEFREENET.EDMONTON.AB.CA> writes:
>>
>> >Anyway, problem is, I burned out before I got to understanding active
>> >analog circuits very well. Now I have a function I want to play with,
>> >that might be more efficient as an analog circuit...
>>
>> The approach you suggest is not practical. It is difficult to get any
>> analog circuit to work to more than 12 bits or so of precision. A
>> circuit that multiplies two variable voltages together cannot be realized
>> with just op-amps (unless tricks are used).
>
>Actually I need to input a 16bit value, and output an 8 bit value, so the
>precision is less than 12 bits. The problem is, that the circuit I need,
>is characterized as a slope type formula... ie: y=mx+b, M tends to
>have relatively small changes between different versions, so to get the
>same result, in an integer I would have to go to a formula with both
>multiplication and division in it. I was hoping to optimize to an easier
>form. (hence the variable gain).
>
>
> Analog multiplier ICs are
>> made but they are kind of specialized and expensive and introduce several
>> more types of error. So you're far, far ahead to do the math in
>> software.
>
>Ok, I suppose that that was part of what I was asking....
>
>>
>> >It involves floating point multiplication so its probably too
>> >expensive
>> >timewise for a PIC.
>>
>> A PIC should be able to do this type of operation about 1000 times per
>> second with nothing too specialized. The figure of 1000 evaluations per
>> second is based on running the PIC at 20 MHz; there are 5000 instructions
>> to do each evaluation. (As an aside, making the analog version work much
>> faster than a few KHz will significantly complicate it).
>
>well that is why I asked, I have no idea what the response rate of an
>active circuit should be in the linear range. Remember however this is
>part of an accellerator circuit, and will be used for massive data arrays,
>so I expect that even a thousand slopes a second, will tend to drag a bit
> ;)
>
>
> If higher
>> speeds are needed then consider a microcontroller with multiply hardware
>> built in. Most of the PIC 17CXXX's have this, as well as a more
>> effective way to place tables of data in the program EPROM. But they are
>> also rather expensive and quirky so you may want to consider a different
>> brand of processor. The various DSP chips are highly optimized for
>> multiplying 16 or 32 bit numbers quickly.
>
>
>I have a 17XX sample or two to work with, so I'll keep this application in
>mind when I start trying to familiarize myself with them.
>
>>
>>
>> If you provide some more details of the formula and the size of numbers
>> to be used, some of the list's numerical experts could probably suggest
>> ways to optimize the computation.
>
>The values range from 1 to 128 for the 8 bit values (xmin), and
>1.0 to 255.0 for the 16 bit values.
>
>There are 63 values between 1.0 and 2.0, for M, of which 1.6XXX has the
>most
>subvalues, at about 5. I might be able to reduce the accuracy to 2 or 3
>sig digits after the point.... but I will have to experiment with that,
>and I am not sure I know how to evaluate the effect on my output. After
>all I want a smooth function, without too much jitter to it.
>
>Essentially what I need to do, is calculate the Y for a slope function
>with a variable slope, and upper and lower limits.
>
>Y = M * (X-Xmin) + -127
>
>is the basic formula.... Simple math.
>
>M is the 16 bit Float, it takes the place of the variable gain. Xmin is
>what we lookup for each entry of M ( by index) X falls within the -127 to
>128 range. I can reduce the storage for the 255 M values, and Xmin values
>because of the particular formula involved to 1/2 of its normal value, but
>that will require some fiddling with the index.
>
>either I need to do hardware multiplication, or I need a full 32K-64K
>lookup table. I can get by with a 32k one, if I can harness the
>orthoganality of the formula at the two byte input level.
>
>If I used a 32K serial eprom lookup, how long would it take to look up the
>third value from the table... Assume a 256 X 128 table and two 8 bit
>values as indexes.
>
>This might be the most cost effective form of accellerator, but I hesitate
>to dump 64k of constants into an eprom unless I know that I need to.
>
>
>
>
>
> My first advice would be at least for
>> now to forget about floating point. It is very rarely necessary in
>> microcontroller applications since the range of values at each step in
>> the process can be determined beforehand. Use binary integers that are
>> scaled so the formula works properly for all possible inputs.
>>
>
>Harder to do than it might look.... I am still fighting with the metaphor
>I am trying to achieve.... It's hard enough to see the metaphor in the
>math right now.... This formula is easy to test, but it lacks the
>sophistication I was hoping for.
>
>>
>Anyway... Thanks for your evaluation of Analog circuit limitations
>
> Grey
>
>The problem is, that the circuit I need,
>is characterized as a slope type formula... ie: y=mx+b, M tends to
>have relatively small changes between different versions, so to get
>the
>same result,
If you're considering a graphical accelerator or vector to raster
converter these problems have been extensively studied and optimized in
the past. There should be plenty of literature available.
>The values range from 1 to 128 for the 8 bit values (xmin), and
>1.0 to 255.0 for the 16 bit values.
Use the 16-bit number as a fixed point with 8 bits of fraction. Then the
high byte is the integer part and the low byte is the fraction (the LSB
is 1/256). So there are 256 evenly spaced increments between 1 and 2 as
well as 2 and 3, etc. The maximum value is 255 + 255/256.
To multiply these numbers by an integer, just multiply in binary. The
the low 8 bits of the result are fraction and the rest is the integer.
>Essentially what I need to do, is calculate the Y for a slope function
>with a variable slope, and upper and lower limits.
>
>Y = M * (X-Xmin) + -127
If you are going compute values of Y for consecutive values of X it is
only necessary to evaluate the whole formula for the first one.
Subsequent values of Y can be obtained by just adding M to the last one.
___________________________________________________________________
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Email will remain constant... at least for now.
On Mon, 14 Jun 1999, Guy Sirton wrote:
> Hi,
>
> I am not sure I understand your problem. Is this pure number
> crunching or a realtime control problem?
> If we're talking number crunching then why are you looking at the
> PIC?
>
Cause I have a few, and the programmer to program em ;)
I'ts actually a bit of both... its the application that is control
oriented, I just need to crunch a lot of numbers to achieve it.... Don't
Ask!
One reason I like the PIC, is I can build a really cheap co-processor
system so I can experiment with adding this to a real computer as a
peripheral.
> On 14 Jun 99, at 0:07, Graeme Smith wrote:
> <snip>
> > Actually I need to input a 16bit value, and output an 8 bit value, so the
> > precision is less than 12 bits. The problem is, that the circuit I need,
> > is characterized as a slope type formula... ie: y=mx+b, M tends to
> > have relatively small changes between different versions, so to get the
> > same result, in an integer I would have to go to a formula with both
> > multiplication and division in it. I was hoping to optimize to an easier
> > form. (hence the variable gain).
>
> What you are describing here is just constant (in the same
> "version") gain and offset. In terms of "quickness" an analog circuit
> with no CPU can be built to perform this function with bandwidth in
> the Ghz range but with a lot of tradeoffs (Noise, linearity, freq/gain
> variations to name a few).
I can concieve of an application where that might be the requirement...
but, at least to start with, I would rather go with the hybrid
digital/analog or just straight digital circuit, so that I can interface
to it.
My experience is that digital development tends to move faster than
straight analog development because it is easier to munge up a new
metaphor.
However if you really think I can get by with a straight analog circuit
in the giga-slope range, it would be worth playing with once the concept
is proven. Stabilizing the circuit would be a real B-kitty.... so I might
need an engineer or two when I get to that point... Not going to be soon,
I would guess.
> If you can live with the tradeoffs there is
> no way any digital system will go faster. You could trim the gain and
> offset manually or control them with a digital system. You can use
> simulation tools such as Spice to try different configuration and get
> an idea of what you'll be getting.
>
No, I need control of the gain as well. One parameter goes to set the
gain, (M) another is a data element, X, and the third is a preset offset
for the particular gain XMIN. What I want to be able to do, is feed the
digital values, in, and read a digital value back out again quickly.
> <snip>
> > Y = M * (X-Xmin) + -127
> I didn't understand from your description where these numbers are
> coming from... If you will be reading them with an A/D from
> somewhere then this could be your bottleneck.
M is derived from Z an 8 bit data element, and represents the slope of the
function, X is a second 8 bit data element, I want to punch in X and Z and
get Y, for any X and Z.
>
> > If I used a 32K serial eprom lookup, how long would it take to look up the
> > third value from the table... Assume a 256 X 128 table and two 8 bit
> > values as indexes.
> >
> > This might be the most cost effective form of accellerator, but I hesitate
> > to dump 64k of constants into an eprom unless I know that I need to.
>
> I believe the newer serial eeproms support a 1Mhz serial clock so
> assuming minimum 32 bits per access it would be 32uS/access
Um... I don't think it is quite that easy.... for instance if I were to
use an I2C rom.... there would be some header, the address, and a code to
be sent, to get an 8 bit data unit. It might be a case of 24 bits in, for
every 8 bits out, but isn't there some latency time involved? 32uS on the
other hand is about 300 times faster than 1mS access time, suggested for
the Floating point math... 1/3 of a Mega-Slope?.... (use "m/" ....;) )
Lets say that 0.3 "m/" is a theoretical maximum for a serial EEprom
> assuming your CPU can keep up (~30Khz). Fast parallel roms offer
> access times in the tens of nanoseconds range.
>
Yes... well, if I am going to interface to a Fast Parrallel Rom, why not
go whole hog, and use a proper MPU, with a built-in bus... in which case
the PIC is a waste of time. I just build an PCI/ISA BUS CARD with a ROM
socket on it.
Still 10nS is approximately 100 mega-slopes
> If this is a one-off thing you should consider using your desktop PC
> with an analog interface card.
>
Its an experimental unit for testing the concept. I can't afford an analog
interface card, (or Spice as far as I know) I had heard that it was
available as shareware or something, but I haven't looked it up yet.
> If you describe your system in more detail (where the inputs are
> coming from and what bandwidth you need), I could try and give
> you more specific ideas.
Its a general proof of concept circuit, there are so many applications
where it might be useful, each with their own specific data requirements
that I would prefer not to move too quickly to a standard bandwidth.
Address has changed with little warning!
(I moved across the hall! :) )
Email will remain constant... at least for now.
On Mon, 14 Jun 1999, Mike Keitz wrote:
> >The problem is, that the circuit I need,
> >is characterized as a slope type formula... ie: y=mx+b, M tends to
> >have relatively small changes between different versions, so to get
> >the
> >same result,
>
> If you're considering a graphical accelerator or vector to raster
> converter these problems have been extensively studied and optimized in
> the past. There should be plenty of literature available.
Nope, as far as I know, nobody else is working on this particular set of
applications yet.... but then, what do I know?
>
> >The values range from 1 to 128 for the 8 bit values (xmin), and
> >1.0 to 255.0 for the 16 bit values.
>
> Use the 16-bit number as a fixed point with 8 bits of fraction. Then the
> high byte is the integer part and the low byte is the fraction (the LSB
> is 1/256). So there are 256 evenly spaced increments between 1 and 2 as
> well as 2 and 3, etc. The maximum value is 255 + 255/256.
>
I was thinking about that.... its still relatively slow, I would think,
and to do it properly I would need a more expensive chip...
> To multiply these numbers by an integer, just multiply in binary. The
> the low 8 bits of the result are fraction and the rest is the integer.
>
> >Essentially what I need to do, is calculate the Y for a slope function
> >with a variable slope, and upper and lower limits.
> >
> >Y = M * (X-Xmin) + -127
>
> If you are going compute values of Y for consecutive values of X it is
> only necessary to evaluate the whole formula for the first one.
> Subsequent values of Y can be obtained by just adding M to the last one.
>
Sorry, not calculating consecutive values, values will vary, depending on
the individual application in ways that are not predictable at this point.
Hi to all engineers.
last night I made a small circuitry to mute the analog line
the pic part works ok but analog section didn't work at all.
on output when I add 10k pull up resister works fine but I can't
do that on audio line.
I connected pic with max4066 analog chip. the problem
I found is that 4066 needs voltage on output to operate
which we do not have it my question is this is there any part that can
be used to mute the analog line "audio" beside relay ?
any help will highly appreciated.
> I connected pic with max4066 analog chip. the problem
> I found is that 4066 needs voltage on output to operate
> which we do not have it my question is this is there any part that can
> be used to mute the analog line "audio" beside relay ?
> any help will highly appreciated.
You can use the 4066, you just have to follow the rules.
The signal voltage must always be inbetween the supply voltages. I'm betting
you used only 0V (ground) and +5V. If you run a line level signal into
this, you'll find horrible distortion, because the analog voltage levels
are - (someting) to +(something) It's the -(something) part that's getting
you in trouble.
Solution #1: Connect VEE to a low negative voltage, at least 1.5V, -5 would
be ideal.
Solution #2: Capacitively couple the signal in and out of the circuit, and
on the input side, use a pair of equal value resistors, say 10k, to bias the
4066 to 2.5V.
I have seen simple muting circuts using either a JFET or even a small
bipolar clamping the signal to ground. The signal is passed through a
largish value resistor first. This is used even on high end car stereos
systems like Kenwood and Alpine.
The analog switch can only operate with analog voltages within its supply
rails. If your analog signal is 0 volts referenced it swings negative and
the analog switch cuts out. You can bias your analog signal as already
suggested.
Also you can use an NPN transistor(2N3904 or PN3904 works very well) to
short to ground the analog signal if the analog signal is less than .5
volts. Experiment with base resistors to reduce pop sound.
> Hi to all engineers.
> last night I made a small circuitry to mute the analog line
> the pic part works ok but analog section didn't work at all.
> on output when I add 10k pull up resister works fine but I can't
> do that on audio line.
> I connected pic with max4066 analog chip. the problem
> I found is that 4066 needs voltage on output to operate
> which we do not have it my question is this is there any part that
> can
> be used to mute the analog line "audio" beside relay ?
> any help will highly appreciated.
>
> Andre
A simple method is to use a light dependent resistor in the audio
line. The LDR is very high resistance when dark, so a no power-mute
would have the LDR in line with the audio followed by a lowish
(2k-10k) resistor to ground. An LED driven by the PIC could enable/
disable it (2 Meg dark to around 5K light).
I have seen this system used but I have not used it personally, I
dont think there would be any significant distortion being a resistive
device but I don't know how linear an LDR is.
The circuit I saw actually used 2 LDRs in a "T" attenuator . That is
in line LDR, resistor to ground, in line LDR.
I've seen this method in "vibrato" generators and avc circuits etc. going
back well into the valve era. However, it would pay to match the wavelength
response of the LDR against the output from the LED. LDRs are, I think,
somewhat more sensitive to green light. ( = Use a green LED ?)
Dave's solution is probably the best way to go, but if you don't have a good
electronics background you will need an explanation of why it works - so
here goes.
(use a fixed font (like Courier) at 80 chars wide to view this diagram
properly).
Audio signal, swinging line held at Audio signal, swinging
-0.6V to +0.6V half +Voltage +1.9V to +3.1V, all DC
--------/------- +5V
|
AC jumps - AC jumps
capacitor | |10K capacitor
| |
| | |_| | |
IN o-----------------| |-----------|-------------4066 switch-----| |---o OUT
| | - | |
| |
| |
|_|10K
|
--------\------- 0V
The incoming audio signal can jump the capacitor. The high value resistors
hold the line into the 4066 switch at a 'fixed' value above 0V, which the AC
is superimposed on to. Because these resistors are high value they won't let
the DC through very quickly, so the fast-changing AC is unaffected on the
input side.
After passing through the switch the AC jumps another capacitor onto a line
that is not DC biased, so the original AC only gets out.
Take care selecting the value of the coupling capacitors, otherwise some
frequencies will be cut off (could be a good thing in some applications like
intercoms, etc).
Can someone else suggest some capacitor values (and what frequencies they
pass/cut) ?
Solution #2: Capacitively couple the signal in and out of the
circuit, and
on the input side, use a pair of equal value resistors, say 10k, to
bias the
4066 to 2.5V.
Should be good as long as the pk-pk audio voltage is less than 5V
The frequency response will depend on the input Z of the following stage -
but assuming it is high enough, the low frequency cut-off will be determined
by the input cap. value & the 2 10k resistors (in AC parallel = 5k)
The a 100nF cap would give you a (low frequency) cut-off (-6dB) of
1/(2*pi*R*C) = 318Hz.
If the following stage is of low Z, use its impedance in parallel with the
10K resistors to work out the cap required for the input side and just the
input Z to work out the output cap. Allow a fair bit of safety factor (2 -
10 times) if possible
The 10k resistors could probably be increased to 100k or even more if low
frequencies are required - but preferably don't use electrolytic caps as any
leakage would lead to distortion.
Here's an interim report on the Sigma-Delta Analog to Digital
converter that I've been playing with.
This provides a VERY low cost analog to digital converter subject to
certain limitations.
I'm getting around 10 bits effective accuracy full scale (9 bits
across the limited range I'm using for reasons summarised below).
- better than on-chip 8 bit A2D converters.
For results accuracies better than a few percent a true comparator or
a gate with a stable and symmetric switching point is needed.
I am using a Z8 with an internal comparator but a PIC, AVR or other
processor with comparator would work equally well.
There's more detail than shown below but this gives enough ideas to
show how it's done.
Russell McMahon
________________________________________
Circuit -
Designate one processor output pin as "feedback pin" = Pfb
Cin = Comparator input state.
Resistor [10K] from unknown voltage to comparator input.
Resistor [10k] from Feedback pin to comparator pin.
Capacitor Cint from comparator pin to ground.
/-----<Pfb
R
R Rf
R
Rin |
Vin ----RRRRR---.------>Cin
|
-
-
|
Gnd
Code:
Assign register Low_Counter
Low_Counter = 0
Set Pfb low until Cin = low
Pfb high till Cin = hi
For N counts
Set Pfb to complement of Cin
If Cin = lo then increment Low_Counter
Next N
Vin unknown is proportional to Low_Counter
NB: The time around the For/Next loop MUST be constant under all
conditions (or else).
Outline:
I find the time constant of Rf//Ri plus Cint can have a major affect
on accuracy - contrary to comments made by some others.
I am currently using a 1uF (!) MKT capacitor but hope to reduce this
for size and cost reasons. Increased resistor sizes (which affect the
time constant in the same way as increased Cint) also have other
affects so care is needed.
I'm getting about +/- 0.2% A2D resolution across a 2 volt range using
a LM324 amplifier to amplify and shift a 0 - 0.2 volt signal to 1 - 3
volt approx. Using Z8 internal comparator. Using 2048 processor loops
at 12uS per loop = 25 ms conversion time. There are all sorts of
potential inaccuracies which are probably not easily addressed
without significant extra expense. Reference is currently divided
decoupled Vcc. Will probably zener regulate this to give enough
stability for this application.
Higher accuracies SHOULD be possible with more conversion loops (and
longer conversion time). I'm considering using a continuous
conversion process where I hold records of say the last 8 conversions
of 100 bits say (to 8 bits) and subtract these from a rolling 16 bit
accumulator every time another 100 sample conversion is completed.
This would allow, in this example, the equivalent of a tracking 8000
sample conversion with a new result available every 100 samples
(every 1.2ms in this case). Whether the consequent affect on response
is acceptable depends on your application.
A single 5v supply is used in this application - a higher voltage if
available will give the 324 a higher common mode range and
accordingly a higher converter range. The LM324 is not a nice
op-amp - where cost is not an utterly driving factor (as it is here)
then the use of a more normal op-amp is indicated. The LM324 does bad
things when its output gets within about 0.6 volts of ground so I
have "translated" the input voltage (0-0.2 volts in my case) up to
about 1 volt and amplified it by a factor of about 10. Adding an
external pulldown to the LM324's output assist its performance when
approaching its lower limit. Spare amplifiers (if any) should be
placed in a defined state - I'm connecting the inverting inputs to
outputs and the non-inverting inputs to the reference voltage. This
keeps the outputs defined and the inputs within the common mode
range.
The LM324 costs $US0.16 in volume and I haven't found any other opamp
which comes close in price.
Any suggestions of a COMPARABLY PRICED but usefully superior amp
would be welcomed.
Changing the Z8 input over from a comparator to a std input pin
produces a result about 10 times worse! - about +/- 2% accuracy!
This demonstrates the advantages of the comparator.
For processors without a comparator a low cost result could be
achieved with an LM339 comparator and LM324 op-amp. If the input
voltage is 0 - 5 volts and low impedance relative to 10K then an
input amplifier MAY be able to be avoided. Note that a non-zero
impedance source will affect accuracy. The LM339 is also a less than
ideal comparator but is slightly cheaper than a 324! In volume a 324
and 339 cost about $US0.30 plus passive R's and C's - the passives
will form an appreciable part of the cost. This would provide up to 4
channels of 10bit (plus, probably) A2D.
> For results accuracies better than a few percent a true comparator or
> a gate with a stable and symmetric switching point is needed.
> I am using a Z8 with an internal comparator but a PIC, AVR or other
> processor with comparator would work equally well.
Russell, when you say "comparator" I start thinking "something compared to
something" but it looks like the Z8 comparator in this case is just
comparing the input voltage to some internally generated mid point. Am I
understanding this correctly?
Years and years ago (I think I was 14) I built R2R D2A on my RCA1802 "Cosmic
ELF" and then connected that to one input of a comparator (seems like I
remember LM339) and an external signal to the other. The comparison was read
by the 1802 and I got about 7 bits accuracy with it after going through
about a gillion resistors to find a matched set (great education in what 5%
tolerance means). I later connected one output pin through a resistor to a
cap to ground and used the top of the cap to feed the comparator instead of
the D2A. I just continually turned on the output pin when the comparator
returned 0 and turned it off when the comparator returned 1. PWM D2A. I
counted the on-time and off-time and calculated the ratio (that was the hard
part on the 1802!). I remember being very happy to get better than 8 bits on
stable input voltages. This is just a voltage follower right? it provides
current gain... so I later hooked up a transistor, audio coupling
transformer and a small speaker and used the uProcessor as an audio
amplifier. Had to decouple the input but it worked ok (some distortion). A
variable resistor acting as a voltage divider between the output pin and the
cap provided variable gain. I was also able to record and play back the
sound by recording the ratios in RAM, then ignoring the comparator and just
modulating the output pin. Had the only talking "Cosmic ELF" on the block!
That was the only thing I ever did that would actually fill up my 4k RAM
board. The grand dream was to do voice recognition... but that was a bit
beyond me at the time. Could never understand FFT or any DSP for that
matter.
Anyway, sorry for the reminiscing but I was trying to say that I think your
continuous conversion idea has merit.
I sandwich a grain of wheat lamp between two LDR's, ( stereo )
slide them into a rubber tube (2.5mm three core flex outer insulation
normally) and seal the ends with black silicone
On the LDR's I use, the resistance varies from ~50 Ohms (light on)
to over 20 MOhms (light off).
I normally supply a second unswitched power source to the lamp
via a pot, so I can use it as a preset attenuator, not full mute.
The attack and decay characteristics of this setup are very pleasing.
The mute time is slow (like a record ending), the attack is a lot faster
but still very smooth ( ~ a quarter second ).
>
> Hi to all engineers.
> last night I made a small circuitry to mute the analog line
> the pic part works ok but analog section didn't work at all.
> on output when I add 10k pull up resister works fine but I can't
> do that on audio line.
> I connected pic with max4066 analog chip. the problem
> I found is that 4066 needs voltage on output to operate
> which we do not have it my question is this is there any part that can
> be used to mute the analog line "audio" beside relay ?
> any help will highly appreciated.
>
> Andre
Here is a simple idea that works really well - it uses just 3 diodes and 1
extra capacitor.
In the common leg of a 3 terminal regulator you add a diode that raises the
regulator's output voltage by the drop across the diode. You then fit 2
identical diodes to the output from the regulator to drop the voltage back
down to where it would have been. Separate smoothing capacitors are then
fitted to the 2 separated outputs.
The really cool thing is that the outputs from the 2 diodes are completely
isolated from each other and can be used to power an analog AND a digital
circuit from the same regulator.
1N4004 diodes that cost less than 10 cents are rated at 1amp/400volts and
470uF caps are about 60 cents, so you can add this second output to your
existing analog power supply for less than a dollar to give you a separate
digital power supply.
part 0 3505 bytes content-type:text/x-vcard; charset=us-ascii; name="vcard.vcf" (decoded 7bit)
Good idea. Does it really cost you 30 cents + 60 cents for 3 diodes and one cap
? Here in India, it costs only 1 cent for 1N4007 and 9 cents for 470 uF / 25V of
a good make in unit quantities. :-)
> Here is a simple idea that works really well - it uses just 3 diodes and 1
> extra capacitor.
>
> In the common leg of a 3 terminal regulator you add a diode that raises the
> regulator's output voltage by the drop across the diode. You then fit 2
> identical diodes to the output from the regulator to drop the voltage back
> down to where it would have been. Separate smoothing capacitors are then
> fitted to the 2 separated outputs.
>
> The really cool thing is that the outputs from the 2 diodes are completely
> isolated from each other and can be used to power an analog AND a digital
> circuit from the same regulator.
>
> 1N4004 diodes that cost less than 10 cents are rated at 1amp/400volts and
> 470uF caps are about 60 cents, so you can add this second output to your
> existing analog power supply for less than a dollar to give you a separate
> digital power supply.
>
> Bye.
>
At 09:54 2/08/99 +0530, you wrote:
>Hi Gennette,
>
>Good idea. Does it really cost you 30 cents + 60 cents for 3 diodes and
one cap
>? Here in India, it costs only 1 cent for 1N4007 and 9 cents for 470 uF /
25V of {Quote hidden}
>a good make in unit quantities. :-)
>
>Pailoor
>
>Gennette Bruce wrote:
>
>> Here is a simple idea that works really well - it uses just 3 diodes and 1
>> extra capacitor.
>>
>> In the common leg of a 3 terminal regulator you add a diode that raises the
>> regulator's output voltage by the drop across the diode. You then fit 2
>> identical diodes to the output from the regulator to drop the voltage back
>> down to where it would have been. Separate smoothing capacitors are then
>> fitted to the 2 separated outputs.
>>
>> The really cool thing is that the outputs from the 2 diodes are completely
>> isolated from each other and can be used to power an analog AND a digital
>> circuit from the same regulator.
>>
>> 1N4004 diodes that cost less than 10 cents are rated at 1amp/400volts and
>> 470uF caps are about 60 cents, so you can add this second output to your
>> existing analog power supply for less than a dollar to give you a separate
>> digital power supply.
>>
>> Bye.
People,
I don't agree with this soultion. In general it only partly covers up the
problem nad is very dependant on the type of three terminal regulator used,
as some will not present large amounts of quiesent current into the ground
pins where others will. Also the dynamic response will create problems that
will induce noise into the analaogue supply by produceing effective ground
bounce as the digital rail is moved around. Also the diode will not be
matched and variances in supplies will occur. This may provide some
problems with low power circuits as one attempts to find the elusive
missing microamps.
So what is my solution?
This depends on the application.
In general there is no reason why the same regulator can not be used to
drive both the digital and analogue supplies as long as the gounds are
seperate and don't transvers the PCB in a // method, and the same for the
supplies. Bring back both the analogue supplies to the regulator and use
MECCA or STAR type single point grounds, inducotr can be used in the supply
line if you require, but should be avoided in the digital supply i.e. Can
be used in the analogue supply.
Dinsmore Instrument Company http://dinsmoregroup.com/dico/ has been
making digital compass products based on switching Hall technology for
some time. They now have a compass module (1655) based on linear Hall
technology. It has two Hall devices at a 90 degree separation and by
reading the two voltages you should be able to determine the direction
of magnetic north. Has anyone already used a PIC (16CE674?) to do this?
For a little more information see my web page:
www.pacific.net/~brooke/Sensors.html#Hall
and in patent 5,157,841 look at figure 3 which shows the drum holding
the permanent magnet supported by two bearings as well as a sensor
mounted close by.
Does anyone know of any Australian distributors of Analog devices products
in small (1 at first if possible) quantities? I am looking at their ADC,
digital pot and analog switch product families.
I have looked at all the listed Australian distributors and only 1 has a web
site and it had no pricing info, and looked bulk only.
At 11:34 20/09/99 +1000, you wrote:
>Does anyone know of any Australian distributors of Analog devices products
>in small (1 at first if possible) quantities? I am looking at their ADC,
>digital pot and analog switch product families.
>
>I have looked at all the listed Australian distributors and only 1 has a web
>site and it had no pricing info, and looked bulk only.
>
>Tom.
>
>
>
> Hi
>
> I want my pic to be able to output 8 bit (more doesn't hurt) 0-1 volt.
>
> I was looking at a MAX522 dual DAC it said it could sink and source 5mA to
> within .5 volts to ground or vdd.
>
> I assume that means that the lowest vout is .5 volts?
>
> Do I need a rail to rail DAC?
> I want to keep component count low any ideas?
>
> Thanks
>
> Jon
> > Hi
> >
> > I want my pic to be able to output 8 bit (more doesn't hurt) 0-1 volt.
> >
> > I was looking at a MAX522 dual DAC it said it could sink and source 5mA to
> > within .5 volts to ground or vdd.
> >
> > I assume that means that the lowest vout is .5 volts?
> >
> > Do I need a rail to rail DAC?
> > I want to keep component count low any ideas?
> >
> > Thanks
> >
> > Jon
A simple NPN transistor will solve your problem, with its base-emitter
voltage drop, 0.6Vdc, isn't?
Just connect the DAC output to any NPN transistor base and at the
emitter you will have DAC-0.6, and by free you have a buffered DAC
output.
+ 5V
|
|
/
|/ NPN
DAC OUTPUT --------| 2N2222 or any other
0.5 to 4.5V |\
v
|
o----------> Output 0 to 3.9V
|
R 500 Ohms to
R 20k
|
GND
You just need to find out which DAC output should be used to generate
the first positive voltage step at the transistor emitter, so that will
be your "zero + 1"
The resistor value should be to match your destination circuit impedance
balanced. If you don't know, just use something around 2k Ohms and it
will work ok.
Another suggestion is just use a silicon diode in series with the DAC
output, it will drop also around 0.6V.
> I was looking at a MAX522 dual DAC it said it could sink and source
> 5mA to within .5 volts to ground or vdd.
> I assume that means that the lowest vout is .5 volts?
No, I think that means it can sink or source 5 milliamps to within
0.5V of either rail, just like a PIC can sink about 15 milliamps to
within 0.5V of either rail.
> Do I need a rail to rail DAC?
I believe the device to which you refer *is* a rail-to rail DAC
according to that specification. If you expect a device to drive
current with *no* voltage drop, you are going to be sorely disappointed;
you require a special component called a "relay" to do that.
Generally, the load to your DAC will be a resistance to ground. The
current that resistance draws is proportional to voltage; the closer to
ground it goes, the less current it draws. If you need to drive 4.5 mA
at 4.5V, you have a load of 1 k ohm. This load will draw 1 mA at 1V,
100 µA at 0.1V and so on. The DAC will drive to ground perfectly since
at that point it delivers *no* current at all!
If OTOH you need it to drive all the way to ground against a pull-up
to the 5V rail, then you *are* going to have a problem and will need a
negative rail to power the op-amp which buffers the ADC. For accuracy
of course, the ADC will still be connected to ground.
At 14:44 7/10/99 +1000, you wrote:
>Jon Petty wrote:
>
>> I was looking at a MAX522 dual DAC it said it could sink and source
>> 5mA to within .5 volts to ground or vdd.
>> I assume that means that the lowest vout is .5 volts?
>
> No, I think that means it can sink or source 5 milliamps to within
>0.5V of either rail, just like a PIC can sink about 15 milliamps to
>within 0.5V of either rail.
>
>> Do I need a rail to rail DAC?
This will depend on the application if rail to rail is required. All DACs
have different output configurations, some have a totem pole driver stage,
and others are of the open collector type etc.
You will need to view the output level with respect to load graphs, and
also have a look at the equation to calculate the output level to see if it
sets an offset (Many do, so the 0.5V may be it, others have .25V etc)
>
> I believe the device to which you refer *is* a rail-to rail DAC
>according to that specification. If you expect a device to drive
>current with *no* voltage drop, you are going to be sorely disappointed;
>you require a special component called a "relay" to do that.
>
This it would seem is a totem pole output and will drive in both
directions, just like a CMOS output will (Except this is linear), so there
is to be an expected (Not always some will not, but very expensive) drop
for where it can not sink or source the current without some voltage loss
(As Paul states)
> Generally, the load to your DAC will be a resistance to ground. The
>current that resistance draws is proportional to voltage; the closer to
>ground it goes, the less current it draws. If you need to drive 4.5 mA
>at 4.5V, you have a load of 1 k ohm. This load will draw 1 mA at 1V,
>100 µA at 0.1V and so on. The DAC will drive to ground perfectly since
>at that point it delivers *no* current at all!
Perhaps the best thing that you can do, is connect this DAC output to a
Rail to Rail OPAMP (Yes even these will not be exact, but they will be
better with an offeset and gain to alter the values to rail to rail), or an
OPAMP driving a single transistor output within the feedback loop (Lets you
use another supply, but does get messey, as does offsets, but these can be
done if the Vref from the DAC is accessable)
>
> If OTOH you need it to drive all the way to ground against a pull-up
>to the 5V rail, then you *are* going to have a problem and will need a
>negative rail to power the op-amp which buffers the ADC. For accuracy
>of course, the ADC will still be connected to ground.
>
> Have I missed something?
> I was looking at a MAX522 dual DAC it said it could sink and source
> 5mA to within .5 volts to ground or vdd.
> I assume that means that the lowest vout is .5 volts?
No, I think that means it can sink or source 5 milliamps to within
0.5V of either rail, just like a PIC can sink about 15 milliamps to
within 0.5V of either rail.
> Do I need a rail to rail DAC?
I believe the device to which you refer *is* a rail-to rail DAC
according to that specification. If you expect a device to drive
current with *no* voltage drop, you are going to be sorely disappointed;
you require a special component called a "relay" to do that.
Generally, the load to your DAC will be a resistance to ground. The
current that resistance draws is proportional to voltage; the closer to
ground it goes, the less current it draws. If you need to drive 4.5 mA
at 4.5V, you have a load of 1 k ohm. This load will draw 1 mA at 1V,
100 µA at 0.1V and so on. The DAC will drive to ground perfectly since
at that point it delivers *no* current at all!
If OTOH you need it to drive all the way to ground against a pull-up
to the 5V rail, then you *are* going to have a problem and will need a
negative rail to power the op-amp which buffers the ADC. For accuracy
of course, the ADC will still be connected to ground.
> > If OTOH you need it to drive all the way to ground against a pull-up
> > to the 5V rail, then you *are* going to have a problem and will need a
> > negative rail to power the op-amp which buffers the ADC. For accuracy
> > of course, the ADC will still be connected to ground.
> >
> > Have I missed something?
I sometimes use the trick of adding a pulldown resistor from the output down to some negative voltage.
The voltage do not need to be very clean as the DAC output usually regulates nicely; a simple diode pump from an available digital clock and RC filter usually works.
Design it to pull down enough so the DAC never needs to pull down, and thus the DAC + pulldown resistor seen as one, can drive your load down to GND with the current of the resistor without having voltage drop in DAC internal low side driver.
Regards
/Morgan
Morgans Reglerteknik, HŠllekŒs, 277 35 KIVIK, SWEDEN
tel +46(0)414-446620, fax -70331, TakeThisOuTmrtiname.com
I'm working on a data logger which is a little different than what I've
done before.
I have three independent circuits (Power, Control, and Monitoring).
Control and Monitoring _may_ share a ground, but this is neither necessary
nor preferred by the customer.
Power must be as isolated from Control or Monitoring as possible, as the
Power circuit gets a lot of noise on it and Control is susceptible to noise :-(
My project is to provide data to the Monitoring system (and ground and
power may both be shared).
Required data:
a) Average Voltage to Power circuit. Power is a 6V-24V source to a 70A
load switched at 3KHz to control motor speed. The motor has a nasty back
EMF spike. We need to see the average voltage during the last 100mS.
b) Average Current in Power circuit. Average current during the last 100mS.
c) Voltage of Control circuit. Control is a 3-6V source for a 75mA-300mA
typical load, with occasional 1A loads. The power supply is well able to
provide 1A with minimal drop for short periods.
d) Voltage of Monitor circuit. Monitor is a 4.5-5.5V source (I'm
investigating whether they will use NiCd or Li technology). It is a PIC
driving an Atmel serial DataFlash chip (which I'm not sure yet, probably
the 4M piece), so it will have bursts of "high" current. Supply will have
no problem providing this.
All data points will be sampled at 10-30 Hz (selected by customer at
runtime, with no hardware changes permitted). 8-bit data is sufficient at
this stage, but they may want 10-12 bit in the future.
The software (PIC) is essentially done - I just borrowed another data
logger I did. The hardware is a problem.
The Monitor circuit is supposed to be small (as small as possible) and
needs to run at least 1 hour on batteries (NiCd rechargeable or Li coin
cells). Of course it's mobile, and will use an RS-232 interface to
transfer data to a laptop, either during operation or at the end of a
testing period.
Test points for the Control circuit is an existing jack into the system
(power and ground are on the connector, not a problem).
Test points for the Power circuit are another matter. A connection to the
positive side of the supply is very easy, and to the negative side almost
as easy. Connection for the ammeter function would be easily accomplished
on either the high side or the low side of the supply, but it needs to
introduce as little resistance as possible (they don't want to hurt
performance of the system).
Now my question:
How do I hook these separate analog signals up without sharing the ground
with the Power circuit?
>I'm working on a data logger which is a little different than what I've
>done before.
<snip>
>
>Now my question:
>
>How do I hook these separate analog signals up without sharing the ground
>with the Power circuit?
>
It sounds as if your customer has SOME budget for moderately expensive
parts. I'd use a 2 port or 3 port isolation amplifier. I've used both the
Burr-Brown 3656 and the Analog Devices AD210 - I prefer the AD part. They
cost about $50 USD and are worth every penny in situations such as yours.
They require a single 15 Vdc power source - this source can be isolated from
both the input and output. The input looks like a standard op-amp - you
treat it as such when setting gain, etc. The output is a unity gain op-amp.
There is auxiliary power available at both the input and output side of the
module. The AD part is good for 10 or 12 bits of accuracy (I don't remember
the exact linearity spec).
PS - the difference between a 2 port and 3 port amplifier: the 2 port
generally shares a common ground between the output and power supply; the 3
port is completely isolated between input, output and power supply. The
AD210 is spec'd at 2500 VAC between input and both other ports; 1000 VAC
between power and output. They are tested and must pass at MUCH higher
voltages than those.
There are other ways around your problem, but the easy ones (much harder
than the isolation amplifier) don't have much accuracy.
>a) Average Voltage to Power circuit. 6V-24V
>b) Average Current in Power circuit. Average current during the last 100mS.
>c) Voltage of Control circuit. Control is a 3-6V source
>d) Voltage of Monitor circuit. Monitor is a 4.5-5.5V source
>All data points will be sampled at 10-30 Hz (selected by customer at
>runtime, with no hardware changes permitted). 8-bit data is sufficient at
>this stage, but they may want 10-12 bit in the future.
>The Monitor circuit is supposed to be small (as small as possible) and
>needs to run at least 1 hour on batteries (NiCd rechargeable or Li coin
>cells). Of course it's mobile, and will use an RS-232 interface to
>transfer data to a laptop, either during operation or at the end of a
>testing period.
>How do I hook these separate analog signals up without sharing the ground
>with the Power circuit?
Depends on what your design constraints are, obviously - how much additional
cost is acceptable, etc... Do you intend to use the internal PIC A/D
converters or
an external part? If you are using an external A/D, is that set in stone
or flexible?
This post intregued me because I've spent the last four years working
on EV telemetry and power systems, and we often face similar problems in
terms of noise,
coupling, floating voltages, and you name it...
Personally, I'd recommend you use true differential delta-sigma A/D
converters - and no,
before everyone jumps on me, these aren't necessarily out of the price
range on any reasonable
project - Analog's AD7705 is a relatively inexpensive (~$4 in small
quantity, I think) dual differential 16 bit D-S A/D that has an
SPI interface and works very nicely under extremely noisy conditions.
Because of the
integration-deintegration performed in the D-S process, noise and random
jitter in the data is reduced
significantly - to the point that one of these was used on the output of a
large (500W) switching power
supply to measure current through a shunt- and had consistent and accurate
average currents out to 10 to 12 bits
without a problem. And with a main ground bus that can have ~2-3 volts of
ripple on it due to currents and inductive
kickback, this is no small feat! Power consumption on these is very
reasonable for battery-based applications - I believe
they can be standby'd to 10uA or so...
If that isn't an option or you would prefer to use some other A/D
converter, just put an instrumentation amp on the
front end - these usually have two drawbacks: they're expensive if you go
for really high-quality versions, and otherwise
their common mode rejection isn't the greatest at higher frequencies.
Since you're only looking for averages, though, you
could R-C integrate off all the high frequencies and leave the in-amp to
only convert the differential input signal you're
trying to monitor down to a "ground" referenced voltage for your circuit to
read. I'm personally a fan of Burr Brown INA2128s, but
these are costly if you actually have to use them in a production circuit.
Analog also makes some very nice ones at lower cost, I
believe. For your application, they also have one other drawback I just
thought of - they're usually current hogs. On the order of ~20mA.
Concerning my earlier post concerning instrumentation amps or differential
ADCs, I feel I should mention
after reading Dwayne's post I rethought my assumption that these signals
are all loosely referenced to some theoretical "ground", your
problem was just that there was excessive noise floating around on the
power ground for the circuit that you didn't want
messing up your readings or coupling back into the signals being sensed...
If that isn't the case, pretty much everything I said is meaningless drivel
and just ignore it...
>If that isn't the case, pretty much everything I said is meaningless drivel
>and just ignore it...
But you said what I wanted to hear - don't take it all back!!!
I think Dwayne interpreted me more correctly. I'm looking to keep these
other systems isolated from the Power system. Not just because of noise,
but because it's possible that they are connected inadvertently and I don't
need to let magic smoke out of somebody else's equipment, let alone mine,
by picking up "ground" in different places.
What I need is some way to measure the Power parameters without being
electrically connected, in a way of thinking. I would opto-isolate if
necessary, etc, but that gets into other problems (like real estate).
As an addendum to the differential A/D and instrumentation amplifiers, and
depending on the precision you require, a standard differential amplifier
using 1,2 or three opamps could be used. As the "common" ground connection
is taken as being a low impedance source, the single op-amp config may well
be adequate. In this configuration run the "common" side to the inverting
input and the "signal" side to the non-inverting input. Common mode error (&
l.f. noise rejection) will be mainly determined by resistor matching so us
1% or better if you need useful accuracy. This will limit any current loops
to the values determined by your input resistors.
If you need better isolation a double op-amp config will give you high input
Z but somewhat limited common mode range. 3 op-amp will give you best
performance overall - but at the expense of realestate.
Suggested opamp - OP177 for low DC drift & offset (I think a quad pack
version is also available now)
I was thinking along the lines of using another PIC (like maybe 12C671)
powered from the motor supply making the motor measurements, but
electrically isolated from everything else, then sending a bit stream
through an optocoupler to the PIC with the EEPROM. It's cheap (<$2 in 25's
from Digikey), tiny (8-pin), and has an 8-bit A/D.
At 03:29 PM 10/28/1999 -0500, you wrote:
>I was thinking along the lines of using another PIC (like maybe 12C671)
>powered from the motor supply making the motor measurements, but
>electrically isolated from everything else, then sending a bit stream
>through an optocoupler to the PIC with the EEPROM. It's cheap (<$2 in 25's
Well, DUH!!! Why didn't I think of that.
You forgot one point - I HAVE THEM IN STOCK!!!! How Stupid can I be!
>At 12:22 PM 10/28/1999 -0500, you wrote:
>>A simple technique requiring a capacitor and DPDT relay:
>>
>>Vx+ >----o | o-----> AtoD
>> |
>> +-)(-+
>> C |
>> +----+
>> |
>>Vx- >----o | o-----> GND
>
>I need to make up to 30 samples/sec. That's a pretty nasty buzz for a
>
>I like the concept, though.
>
>Other ideas?
>
>Thanks.
>
>Andy
>==================================================================
> Eternity is only a heartbeat away - are you ready? Ask me how!
>------------------------------------------------------------------
>.....andyRemoveMErc-hydros.comhttp://www.rc-hydros.com - Race Boats
>KILLspamandyTakeThisOuTmontanadesign.comhttp://www.montanadesign.com - Electronics
>==================================================================
>
This is a "flying capacitor" analog isolator. As I recall, Maxim makes
a chip that does this.
Harold
On Fri, 29 Oct 1999 11:28:36 +0100 fernteix <TakeThisOuTfernteixspam_OUTTELEWEB.PT> writes:
> Hi
>
> Use the same idea with analogue swiches.
>
> fernando
>
> {Original Message removed}
At 10:31 AM 10/28/99 -0600, you wrote:
>>I'm working on a data logger which is a little different than what I've
>>done before.
>
><snip>
>
>>
>>Now my question:
>>
>>How do I hook these separate analog signals up without sharing the ground
>>with the Power circuit?
>>
This is similar to a problem I was just working on. We were measuring
current loops, so we could power the isolated side of the circuit. I'm not
sure if that's an option for you here. What we did is basically just power
an AD off of the current loop via a zener and send the serial signals
through optoisolators.
Some of the other things we thought about are :
1: analog optoisolators .... really crappy temp coefficient kills your
accuracy over temp.
2: Voltage to frequency using op-amps then through opto isolators or caps.
Uses a fair amount of power on the iso side. This problem can be solved by
having a truly isolated supply on the other side using a transformer.
3: A sort of charge sharing setup where storage caps are switched from iso
circuit to internal circuit. I never quite got this one, but the EE's tell
me it should work.
4: Voltage to PWM through opto-isolators. Also somewhat of a power hog and
sort of complicated.
I am looking for a circuit that will convert a 0-100 duty cycle at 15 Hz to a
0-5v analog signal to send to the ad converter. 50% duty= 2.5v. There are
some timing reasons why I don't want to measure the pulses directly. The
analog voltage still needs to be responsive with a refresh rate of at least
10Hz, so a large cap (1000 uF) makes the response to slow. I found lots of
circuits for converting voltage to a variable duty cycle or frequency to
voltage, but nothing for duty to voltage.
> I am looking for a circuit that will convert a 0-100 duty cycle at 15 Hz to a
> 0-5v analog signal to send to the ad converter. 50% duty= 2.5v.
This is a "PWM DAC", essentially. I have a circuit that I commonly use
for creating 4-20mA current loop driver signals that does this. Requires
a dual op-amp, a couple of transistors (V-I converter) and a few resistors
and caps. This thing is driven off a PIC output pin at 40Hz in most of
my stuff, but with some minor tweaks (double the integrating cap value)
it should work fine at 15Hz. Making it do 0-5V is also a simple circuit
change.
Send a private email if you want the schematic (as soon as I scan it ;)
As far as I know, duty to voltage converters are simply low-pass filters.
In your case cut-off frequency of the filter is very near to the pulse
carrier frequency. To filter 15 Hz out of signal with an LP filter with 10
Hz cut-off frequency you will need very high order filter - Is it realistic?
Why simply not use interrupts on edges of the PWM signal and read timer
value at these moments? It takes only about 20 instructions to convert timer
samples to the pulse width. With constant PWM frequency you can use look-up
table to convert pulse width to analog value.
I used the same approach to read output of Analog Devices TMP03 temperature
sensor - It has floating frequency of 20-40 Hz and needs about 120 kHz
sampling rate to get accurate measurement. Worst of all, it needs both pulse
width and period measurement :)
> Why simply not use interrupts on edges of the PWM signal and read timer
> value at these moments? It takes only about 20 instructions to
> convert timer
> samples to the pulse width. With constant PWM frequency you can
> use look-up
> table to convert pulse width to analog value.
If you need a 'flying cap' front end, you may want to take a look at the
LTC1043 Dual Precision Instrumentation Switched-Capacitor Building Block
from Linear Tech at http://www.linear-tech.com/
>I would really like to see how you did this.
>
>Wanna share ??
>
>> Why simply not use interrupts on edges of the PWM signal and read timer
>> value at these moments? It takes only about 20 instructions to
>> convert timer
>> samples to the pulse width. With constant PWM frequency you can
>> use look-up
>> table to convert pulse width to analog value.
>
>
Why not. Don't know if it will be useful to you, because the routine is very
specific.
Here is the setup:
TMP03 connected to RB0.
TMR0 programmed to run from internal clock (4 Mhz crystal) with 1:8
prescaler. The timer is free running, without corrections to TMR0 register.
This snippet measures time of pulse in high state TMP_T1L, TMP_T1H and time
of pulse in low state TMP_T2L, TMP_T2H. The main program uses these values
to compute temperature. To read the values the main program polls ready flag
TMP_READY.
On timer overflow there is a correction to high byte. Because timer overflow
handler does some other stuff I use nested interrupts (BSF INTCON, GIE).
This is unnecessary if you move the timer overflow handler in the main
program.
Note that the routine is designed for TMP03 sensor, which never has 0% or
100% duty cycle.
Is this what you wanted?
Bye
-----------------------------------------------------------
;**** temperature measure
MOVF TMR0, W
;if after rb0 front the timer overflowed then
;use value 255 as the most near value to the truth
BTFSC INTCON, T0IF
MOVLW 255
If this is for the TMP-03 sensor you may wish to
consider a routine Dwayne Reid wrote. IIRC, it uses an
interlaced co-routine type trick to poll a pulse and
achieve 3 tcyc resolution in the measurement and have
16-bit dynamic range. I presume you can obtain similar
results with TMR0 by setting the prescaler to 0 (i.e.
give the WDT the prescaler), polling TMR0 rollovers,
and polling the pulse. However, since there are two
things that have to be polled you'd only be limited to
4 or 5 Tcyc resolution (that is if you're lucky or
clever - which ever comes first)
hi Nikolai ,
your approach sounds great !!
if you do decide to make it available to others , please put me on your list .
TFYT,
Glen
i have sent this to you privately !
*****************
> As far as I know, duty to voltage converters are simply low-pass filters.
> In your case cut-off frequency of the filter is very near to the pulse
> carrier frequency. To filter 15 Hz out of signal with an LP filter with 10
> Hz cut-off frequency you will need very high order filter - Is it realistic?
> Why simply not use interrupts on edges of the PWM signal and read timer
> value at these moments? It takes only about 20 instructions to convert timer
> samples to the pulse width. With constant PWM frequency you can use look-up
> table to convert pulse width to analog value.
> I used the same approach to read output of Analog Devices TMP03 temperature
> sensor - It has floating frequency of 20-40 Hz and needs about 120 kHz
> sampling rate to get accurate measurement. Worst of all, it needs both pulse
> width and period measurement :)
>
> Cheers
> Nikolai
>
>If this is for the TMP-03 sensor you may wish to
>consider a routine Dwayne Reid wrote. IIRC, it uses an
>interlaced co-routine type trick to poll a pulse and
>achieve 3 tcyc resolution in the measurement and have
>16-bit dynamic range. I presume you can obtain similar
>results with TMR0 by setting the prescaler to 0 (i.e.
>give the WDT the prescaler), polling TMR0 rollovers,
>and polling the pulse. However, since there are two
>things that have to be polled you'd only be limited to
>4 or 5 Tcyc resolution (that is if you're lucky or
>clever - which ever comes first)
No, thanks.
Resolution is pretty, but PIC is kept busy while doing pulse measurement.
Because pulse frequency is as low as 20-40 Hz it means blinking LED
indicator. :)
BTW, what "interlaced co-routine" means? Is it interlaced with other routine
or something?
> BTW, what "interlaced co-routine" means? Is it
> interlaced with other routine
> or something?
Yeah.
In the simplest case, 'co-routines' may be thought of
multi-tasking with just two tasks: task_A & task_B.
task_A gets control (somehow), runs for a while,
suspends, and then calls task_B. task_B then does the
same thing. The point at which the two tasks suspend
is saved in some kind of context. For example, task_A
will save a point to the address where it would like
to begin executing the next time it gets control.
Now, what makes a co-routine different from a
full-blown multi-tasking OS is that the information
stored in a task's state is much simpler. For example,
instead of storing pointers to addresses you may
decide to retain a 'state variable' that serves as an
index into an array of address from which a task may
begin executing. So when task_A decides to relinquish
control, it may increment its state variable and then
call task_B's state table. I've seen multi-tasking
OS's that take this kind of approach too. The only
difference is that the co-routine approach doesn't go
through a multi-tasking middle layer; task_A always
passes control to task_B (and vice versa).
With a PIC, you may take this concept to the extreme.
The 'multi-tasking' / 'co-routine' can be encoded
directly in the programming. In Dwayne's case, there
were two tasks to be performed: poll on an I/O line
and determine when it has changed states AND measure
how lon it had taken to make that change. So the code
was tightly inter-twined like so:
loop:
btfsc port,bit
goto bit_is_high_1
movlw DELTA
btfsc port,bit
goto bit_is_high_2
addwf total_count_lo,f
btfsc port,bit
goto bit_is_high_3
rlf known_zero,w ;get the carry
btfsc port,bit
goto bit_is_high_4
addwf total_count_hi,f
btfss port,bit
goto loop
;labels for bit_is_high_ 1,2,3,4 are here
IIRC, Scott and Reggie provided enhanced versions of
both of these. But Scott's no longer subscribed and I
haven't seen anything from Reggie for quite some time.
.lo
=====
__________________________________________________
Do You Yahoo!?
Bid and sell for free at http://auctions.yahoo.com
Thanks for all the replies. I was at a trade show with no modem port to reply
to your responses. I'll be reviewing them over the next couple of days, but
thanks again for the help
> As far as I know, duty to voltage converters are simply low-pass filters.
> In your case cut-off frequency of the filter is very near to the pulse
> carrier frequency. To filter 15 Hz out of signal with an LP filter with 10
> Hz cut-off frequency you will need very high order filter - Is it
realistic?
> Why simply not use interrupts on edges of the PWM signal and read timer
> value at these moments? It takes only about 20 instructions to convert
timer
> samples to the pulse width. With constant PWM frequency you can use
look-up
> table to convert pulse width to analog value.
> I used the same approach to read output of Analog Devices TMP03 temperature
> sensor - It has floating frequency of 20-40 Hz and needs about 120 kHz
> sampling rate to get accurate measurement. Worst of all, it needs both
pulse
> width and period measurement :)
>
> Cheers
> Nikolai >>
> BTW, what "interlaced co-routine" means? Is it
> interlaced with other routine
> or something?
Yeah.
In the simplest case, 'co-routines' may be thought of
multi-tasking with just two tasks: task_A & task_B.
task_A gets control (somehow), runs for a while,
suspends, and then calls task_B. task_B then does the
same thing. The point at which the two tasks suspend
is saved in some kind of context. For example, task_A
will save a point to the address where it would like
to begin executing the next time it gets control.
Now, what makes a co-routine different from a
full-blown multi-tasking OS is that the information
stored in a task's state is much simpler. For example,
instead of storing pointers to addresses you may
decide to retain a 'state variable' that serves as an
index into an array of address from which a task may
begin executing. So when task_A decides to relinquish
control, it may increment its state variable and then
call task_B's state table. I've seen multi-tasking
OS's that take this kind of approach too. The only
difference is that the co-routine approach doesn't go
through a multi-tasking middle layer; task_A always
passes control to task_B (and vice versa).
With a PIC, you may take this concept to the extreme.
The 'multi-tasking' / 'co-routine' can be encoded
directly in the programming. In Dwayne's case, there
were two tasks to be performed: poll on an I/O line
and determine when it has changed states AND measure
how lon it had taken to make that change. So the code
was tightly inter-twined like so:
loop:
btfsc port,bit
goto bit_is_high_1
movlw DELTA
btfsc port,bit
goto bit_is_high_2
addwf total_count_lo,f
btfsc port,bit
goto bit_is_high_3
rlf known_zero,w ;get the carry
btfsc port,bit
goto bit_is_high_4
addwf total_count_hi,f
btfss port,bit
goto loop
;labels for bit_is_high_ 1,2,3,4 are here
IIRC, Scott and Reggie provided enhanced versions of
both of these. But Scott's no longer subscribed and I
haven't seen anything from Reggie for quite some time.
.lo
=====
__________________________________________________
Do You Yahoo!?
Bid and sell for free at http://auctions.yahoo.com
> In the simplest case, 'co-routines' may be thought of
> multi-tasking with just two tasks: task_A & task_B.
I commonly use this in PICs (and other micros) to operate the A/D. I
set TMR0 to interrupt at 2x the sample rate, and in interrupt service
either sampling to the track-and-hold is done (state 1) or the conversion
is started (state 2). I pick up the conversion result at the beginning of
the next sample service state.
>IIRC, Scott and Reggie provided enhanced versions of
>both of these. But Scott's no longer subscribed and I
>haven't seen anything from Reggie for quite some time.
I posted the orginal question and several very helpful souls found the
answer I am now using. The core of the routine came from Scott Dattalo. Enjoy!
The following is snipped from one of my messages to Scott:
BTW: the code works VERY well. Its being used to measure the pulse duty
cycle ratio from Analog Devices TMP03 / 04 temperature sensors and can
resolve down to fractins of a degree (far more accuracy than the sensor). I
cleaned the normalize part of the routine up slightly as follows at the end
of this message.
The entire measurement routine (wait for HI, wait for LO, measure LO,
measure HI, test for noisy signal, normalize everything, multiply HI pulse
by constant, divide by LO pulse, average 16 samples) takes about 400 code
spaces - left me lots of room for the rest of the project in a 12c508.
;up to 19 bit pulse timer with 3 cycle resolution
;concept by Scott Dattalo, this version by Dwayne Reid
;now measure HI period
clrf MH_low
clrf MH_mid
clrf MH_high ;used as known zero for main loop
MH_loop
btfss PULSE
goto MH_1st
movlw 1
btfss PULSE
goto MH_2nd
addwf MH_low,F
btfss PULSE
goto MH_3rd
rlf MH_high,W ;get C into W (add 0 or 1 to next byte)
btfss PULSE
goto MH_4th
>Thanks Dwayne for your version of pulse measurement routine.
>The code is so spaghetti like, and I really enjoyed digesting it :-)) Took
>some time!!
>
>Regards,
>Nikolai
No problem! It IS spaghetti-like, but it lets a 4 MHz 12c508 measure pulses
with 3 uS resolution. As I mentioned earlier, Scott Dattlo and Reggie
Bergin get most of the credit for it.
>>Thanks Dwayne for your version of pulse measurement routine.
>>The code is so spaghetti like, and I really enjoyed digesting it :-)) Took
>>some time!!
>>
>>Regards,
>>Nikolai
>
>
>No problem! It IS spaghetti-like, but it lets a 4 MHz 12c508 measure
pulses
>with 3 uS resolution. As I mentioned earlier, Scott Dattlo and Reggie
>Bergin get most of the credit for it.
>
>dwayne
>
I think this is a very good routine too. Though it has some dead time and
can skip small pulses greater then 3 uS. This is because there is some time
between detection of low pulse end and starting to poll for high pulse end
:)
I am looking for a "simple as possible" preamp circuit to connect to a VCA
and allow the Audio imput to switch between Mic and Line Level with a gain
pot if possible.
There are always those preamps made with 4000 series CMOS Logic parts?
Pretty simple, but I haven't done one in a long time (You let the
inverters act as an oscillator, they generate a voltage proportional to
your audio signal, anyone have the design handy? If I were done moving,
... <G>)
Some of the below may be duplicates mirrored, just quick possibilities
for you:
Also, ftp://ftp.unina.it/pub/electronics/cookbook/video/kuckuck.zip is
about using a DRAM chip as an optical imaging device. Interesting page
there <G>
>
> Hi,
>
> I am looking for a "simple as possible" preamp circuit to connect to a VCA
> and allow the Audio imput to switch between Mic and Line Level with a gain
> pot if possible.
>
> Thanks
>
> Mathew Cohen
--
I do small package shipping for small businesses, world-wide.
If anyone has any documentation on servo control signals, would you be so
kind
as to mail it to me please.
(Assume I know nothing about servo control signals).
I want to read a servo control signal and convert it into an analogue
voltage (say
0 to 5V) - using perhaps pwm with a pic.
If anyone has done anything similar please e-mail me direct.
Darren,
By servos I assume you mean hobby servos like those used in radio control
cars and airplanes. To control these with a PIC (or read the signal) is
very simple. The R/C receiver sends an on pulse to the servo that lasts
between 1 and 2 milliseconds depending on the position of the
corresponding stick on the transmitter. It repeats these pulses every
20ms (the total period is 20ms, so if the on signal is 1ms the off signal
is 19ms and if the on pulse is 2ms the off period is 18ms). So the
pulses are being transmitted at a frequency of 50Hz. A 1ms on pulse will
rotate the servo all the way in one direction, a 2ms pulse all the way in
the other direction, and a 1.5ms pulse will center the servo. So a
centered servos control pulse will look like:
-----_______________-----________________
On for 1.5ms, off for 18.5ms on for 1.5ms, off for 18.5, etc.
Some servos can be driven beyond the 1 and 2ms limits described here, but
1 and 2ms are the normal limits. I have also seen pulse frequencies as
high as 80Hz and as low as 5Hz. With some servos the higher the pulse
frequency the more torque and holding power the servo provides.
To read the incoming pulses I would hook the line coming from the R/C
receiver to an input port on the PIC that can trigger an interrupt.
Set/reset a counter when the interrupt occurs, then watch for the next
change on that port. I have use the PORTB change interrupts on a
16C(F)84 quite successfully for this measurement.
Someone else will have to help with converting to a voltage.
> Hi
>
> If anyone has any documentation on servo control signals, would
> you be so
> kind
> as to mail it to me please.
> (Assume I know nothing about servo control signals).
>
> I want to read a servo control signal and convert it into an
> analogue
> voltage (say
> 0 to 5V) - using perhaps pwm with a pic.
>
> If anyone has done anything similar please e-mail me direct.
>
> Thanks a million in advance.
>
> Regards,
> Darren Logan BSc
Adam Bryant (age 0x23) spamadamdbspam_OUTjuno.com
Parker, CO, USA
Robotics, RC Airplanes, anything using a PIC
___________________________________________________________________
Why pay more to get Web access?
Try Juno for FREE -- then it's just $9.95/month if you act NOW!
Get your free software today: dl.http://www.juno.com/dynoget/tagj.
Well, I put together some informations about servos (controlled by lpt
port on a pc running win 95, but still interesting if you know nothin
about servos) :
>
> Hi
>
> If anyone has any documentation on servo control signals, would you be so
> kind
> as to mail it to me please.
> (Assume I know nothing about servo control signals).
>
> I want to read a servo control signal and convert it into an analogue
> voltage (say
> 0 to 5V) - using perhaps pwm with a pic.
>
> If anyone has done anything similar please e-mail me direct.
>
> Thanks a million in advance.
>
> Regards,
> Darren Logan BSc
> Well, I put together some informations about servos (controlled by lpt
> port on a pc running win 95, but still interesting if you know nothin
> about servos) :
OK, firstly your webpage omits the ground connection to the printer
port connector. I think you should have shown that clearly as some
people will otherwise complain of very peculiar behaviour.
You mention obtaining 5V to operate the servos from the PC, and note
the risk involved. The risk may be minimised by using a device called
a "fuse" appropriately.
The most convenient source for this 5V is the joystick connector where
this is on a separate sound card - at worst you will torch the sound
card.
You can use the keyboard socket with a "piggyback" connector but not
all motherboards have polyswitches (or fuses) fitted and I for one am
getting sick of repairing burn holes in motherboards. (Recall my post
on the damage caused by the excremental USB adaptor?)
Finally, and along the same lines, I do recommend the use of a printer
adaptor card for experimentation, best one of the old ones using 74LS
chips as they are actually repairable, modifiable (to bi-directional
use) and adaptable to non-standard printer addresses.
--
Cheers,
Paul B.
> Finally, and along the same lines, I do recommend the use of a printer
> adaptor card for experimentation, best one of the old ones using 74LS
> chips as they are actually repairable, modifiable (to bi-directional
> use) and adaptable to non-standard printer addresses.
I would certainly agree - but it's pretty hard to find those old 74LS TTL
based printer port cards. Before they disappeared, they were as cheap
as the single chip ones are today. The last ones I got even had full
sockets for all chips, for around $15. Easy to repair, or change logic
families (I liked 74ACT). Any IO address, bidirectional modifiable in a
few minutes with a soldering iron.
Zhahai Stewart wrote:
>
> > Finally, and along the same lines, I do recommend the use of a printer
> > adaptor card for experimentation, best one of the old ones using 74LS
> > chips as they are actually repairable, modifiable (to bi-directional
> > use) and adaptable to non-standard printer addresses.
>
> I would certainly agree - but it's pretty hard to find those old 74LS TTL
> based printer port cards. Before they disappeared, they were as cheap
> as the single chip ones are today. The last ones I got even had full
> sockets for all chips, for around $15. Easy to repair, or change logic
> families (I liked 74ACT). Any IO address, bidirectional modifiable in a
> few minutes with a soldering iron.
>
> Know of any sources today?
Again, I fully agree, however you won't get one new today of course, but
you can get equivalents. They don't have the simple 74 family stuff, but
at $19USD I guess it doesn't matter a lot. If it protects your computer
at that price.
jdr.com has one example "MCT-1P" $19.99
Perhaps there is even a market for a small 74xx type single port card at
the right price.
>
> Zhahai Stewart wrote:
> >
> > > Finally, and along the same lines, I do recommend the use of a printer
> > > adaptor card for experimentation, best one of the old ones using 74LS
> > > chips as they are actually repairable, modifiable (to bi-directional
> > > use) and adaptable to non-standard printer addresses.
> >
> > I would certainly agree - but it's pretty hard to find those old 74LS TTL
> > based printer port cards. Before they disappeared, they were as cheap
> > as the single chip ones are today. The last ones I got even had full
> > sockets for all chips, for around $15. Easy to repair, or change logic
> > families (I liked 74ACT). Any IO address, bidirectional modifiable in a
> > few minutes with a soldering iron.
> >
> > Know of any sources today?
>
> Again, I fully agree, however you won't get one new today of course, but
> you can get equivalents. They don't have the simple 74 family stuff, but
> at $19USD I guess it doesn't matter a lot. If it protects your computer
> at that price.
>
> jdr.com has one example "MCT-1P" $19.99
>
> Perhaps there is even a market for a small 74xx type single port card at
> the right price.
>
> Don McKenzie EraseMEdonRemoveMEdontronics.comhttp://www.dontronics.com
>
> World's Largest Range of Atmel/AVR and PICmicro Hardware and Software.
> Free Basic Compiler and Programmer http://www.dontronics.com/runavr.html
http://www.computergate.com/ has a $7.99 part, part number "ONPP", 8-bit
card, not bi-dir; looking at the one I have here, it's a 1-chip
solution card, really inexpensive. It's a "fuse", works well for
dot-matrix printers or prototyping programmers.
I'll start keeping an eye out for old style LPT cards, seems like I've
been passing on those occasionally at computer shows here.
Mark
--
I re-ship for small US & overseas businesses, world-wide.
(For private individuals at cost; ask.)
Mark Willis wrote:
> http://www.computergate.com/ has a $7.99 part, part number "ONPP", 8-bit
> card, not bi-dir; looking at the one I have here, it's a 1-chip
> solution card, really inexpensive. It's a "fuse", works well for
> dot-matrix printers or prototyping programmers.
That chip on the card probably has a bi-direction
enable/disable pin that the cardmaker just hard wired one
way. A resistor and a piece of wire will fix this defect..
But most are wimpy and blow out easily.
One of the best printer port card makers is LAVA. Don't
remember the url (is not lava.com) but search, they have a
site. Guaranteed for life. Mine has been tortured (got it
for $3 in a junk bin!) and still works. You break it, just
send it to them and they send a new one (or the closest
match for older cards).
> OK, firstly your webpage omits the ground connection to the printer
> port connector. I think you should have shown that clearly as some
> people will otherwise complain of very peculiar behaviour.
Well, you're right on the whole thing : I made this for simple testings.
The only advantage of this design is the fact that you don't need to
open your computer, nor add a new card. But the biggest problem, as you
mentionned, is the risk for your lpt port.
Anyway, thanks for the comments. May I add them to the web page?
>
> You mention obtaining 5V to operate the servos from the PC, and note
> the risk involved. The risk may be minimised by using a device called
> a "fuse" appropriately.
>
> The most convenient source for this 5V is the joystick connector where
> this is on a separate sound card - at worst you will torch the sound
> card.
>
> You can use the keyboard socket with a "piggyback" connector but not
> all motherboards have polyswitches (or fuses) fitted and I for one am
> getting sick of repairing burn holes in motherboards. (Recall my post
> on the damage caused by the excremental USB adaptor?)
> Finally, and along the same lines, I do recommend the use of a printer
> adaptor card for experimentation, best one of the old ones using 74LS
> chips as they are actually repairable, modifiable (to bi-directional
> use) and adaptable to non-standard printer addresses.
"Paul B. Webster VK2BZC" wrote:
>
> Philippe Jadin wrote:
>
> > Well, I put together some informations about servos (controlled by lpt
> > port on a pc running win 95, but still interesting if you know nothin
> > about servos) :
>
> > goto http://users.swing.be/philippe.jadin/servoen.htm
>
> OK, firstly your webpage omits the ground connection to the printer
> port connector. I think you should have shown that clearly as some
> people will otherwise complain of very peculiar behaviour.
You also talk on your web page of pulse lengths of 1.5 to 2 millisecs.
AFAIK 1.5 millisecs is servo centre with 1 millisecs minimum and 2
millisecs maximum position of the servo. Also don't use 1 millisec and 2
millisecs as absolutes, as it can damage some servo's. Rather keep it
between 1.2 and 1.8 millisecs to be safe.
Servo signals vary widely among manufacturers. I took an article on faith
that claimed 0.5 to 2.5 milliseconds was the right signal range. Worked
great on one servo. Bought another servo, and it was acting a little funny
around the end of travel. the second time it hit the end stop it went
"POP!" and never worked again. OOPS it was a 1 to 2 ms servo. You can
NEVER tell this info from the packages, you have to just call the mfr and
ask their tech heads. Don't guess.
SILVER LINING: So I took apart the servo, and removed the busted pot and
the stops. Replaced it with an external 5K linear pot. Now my servo drives
a little nonlinear mechanism (cams and stuff) that is linearized because
the feedback is an external linear pot! Much improved. I have another
servo that I replaced the pot with fixed resistors and removed the stops.
Instead of position, the input signal determined speed and direction. If
you hack a servo this way (they are EMINENTLY hackable!) you can go outside
the mfrs. signal specs quite a bit.
I fell in love with servos about a year ago, having ignored them all this
time. Servos are great little packages of cheap mass produced technology!
They were born to marry the PIC.
mindlink.bc.ca) But now he'll drink no more,
