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PICList Thread
'How to turn it off'
1997\12\19@084550 by Octavio Nogueira

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Regards,

Octavio
======================================================
Octavio Nogueira  - e-mail:   spam_OUTnogueiraTakeThisOuTspammandic.com.br
http://www.geocities.com/~oct_nogueira
"ProPic" Production PIC Programmer Windows under US$20
======================================================

Attachment converted: wonderland:liga2.GIF (GIFf/JVWR) (0000E534)

1997\12\19@090711 by paulh

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part 0 1317 bytes content-type:TEXT/PLAINOn Fri, 19 Dec 1997, Octavio Nogueira wrote:

> I'm developing a battery operated device with 16C71 and I need the 16C71
> to turn the power off. I thought in a transistor controlled by RA4.

Shouldn't there be a voltage regulator there somewhere?  When the circuit
is on, the 16C71 will get almost 9 volts to Vdd.  RA4 should be fine, but
I don't think 16C71's come in a version rated for 9 volts.

> Please take a look in the attached file (just 2K) and say if it's safe.

I put the image on my website for digest subscribers, and others who are
attachment impaired.  It is at:
     http://www.hamjudo.com/liga2.gif

> Or, does anyone have a better idea?

You need a voltage regulator after the transistor.  I'm afraid I don't do
transistor designs often enough to tell you if the resistors have
reasonable values, or if the transistor is in right.

> Regards,

> Octavio
> ======================================================
> Octavio Nogueira  - e-mail:   .....nogueiraKILLspamspam@spam@mandic.com.br
> http://www.geocities.com/~oct_nogueira
> "ProPic" Production PIC Programmer Windows under US$20
> ======================================================
>

--
paulhspamKILLspamhamjudo.com  http://www.hamjudo.com
The April 97 WebSight magazine describes me as "(presumably) normal".

1997\12\19@093608 by Brian Schousek

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For one thing, this circuit supplies the PIC with 9V (minus vce of the
transistor of course) which will result in one thing: an unhappy PIC. You
should have a voltage regulator somewhere in the circuit, preferably *after*
the transistor (to cut down on the leakage current when power is off)
If somebody complains about the ~8.3V seen on RA4 when power is off, see the
thread elsewhere on the list lately talking about this.

Brian
{Original Message removed}

1997\12\19@102231 by Martin R. Green

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One question about your design.  Is the switch momentary contact?  If
not, I see no way your circuit will work.  I assume you intend the PIC
to start up when the button is pressed and set up RA4 as an output and
drive it low (I suggest you set it low first, before setting it up as
an output to prevent any risk of RA4 trying to drive high while the
button is pressed), thus latching the PIC power on, even after the
button is released.

CIAO - Martin.

On Fri, 19 Dec 1997 11:43:45 -0200, Octavio Nogueira
<.....nogueiraKILLspamspam.....MANDIC.COM.BR> wrote:

{Quote hidden}

Martin R. Green
elimarspamspam_OUTNOSPAMbigfoot.com

To reply, remove the NOSPAM from the return address.
Stamp out SPAM everywhere!!!

1997\12\19@115034 by Dmitry Kiryashov

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Octavio Nogueira wrote:
>
> I'm developing a battery operated device with 16C71 and I need the 16C71
> to turn the power off. I thought in a transistor controlled by RA4.
> Please take a look in the attached file (just 2K) and say if it's safe.
> Or, does anyone have a better idea?

Two suggestions:

1. Voltage source: PIC voltage operating range is 2.5v to 6v .
  Use another voltage battery or apply voltage regulator.

2. Add capacitor aproximatly 20uF after switch , i.e. in parallel with
  PIC power supply pins ("+" capacitor to Vdd and "-" to Vss PIC pins)

WBR Dmitry.

1997\12\19@123307 by DREITEK

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In a message dated 97-12-19 08:48:00 EST, you write:

<<
I'm developing a battery operated device with 16C71 and I need the 16C71
to turn the power off. I thought in a transistor controlled by RA4.
Please take a look in the attached file (just 2K) and say if it's safe.
Or, does anyone have a better idea?

Regards,

Octavio >>
Hello Octavio!
I have accomplished this in the past using a voltage regulator with a powerup
input.
(Toko makes them as well as Maxim.  Digikey sells them both)
I havent looked at your file yet so the may be redundant but this tecnique
worked well for my app.  I has a momentary push button that turned the unit
on.  It stayed on for a [eriod of time and then turned itself off.  The push
button was wired to the Battery+ and to the power up of the regulator.  The
power up input of the regulator is also wired to a bit on the PIC.  The first
thing the software does on powerup is to turn that bit into an output and
bring it true.  This keeps the  regulator turned on.  When it is time to turn
off, simply bring the output bit false and all turns off.

If you need more just hollar.

Dave Duley

1997\12\20@044912 by Octavio Nogueira

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>One question about your design.  Is the switch momentary contact?  If
>not, I see no way your circuit will work.  I assume you intend the PIC
>to start up when the button is pressed and set up RA4 as an output and
>drive it low (I suggest you set it low first, before setting it up as
>an output to prevent any risk of RA4 trying to drive high while the
>button is pressed), thus latching the PIC power on, even after the
>button is released.
>
>CIAO - Martin.

Thanks to all that respond my question and,

Yes, the switch is momentary, there is a 5V regulator after the transistor,
what I'm worried about is the 8.3V in the RA4 when the circuit is off. Is
this safe?

Regards,

Octavio

======================================================
Octavio Nogueira  - e-mail:   @spam@nogueiraKILLspamspammandic.com.br
http://www.geocities.com/~oct_nogueira
"ProPic" Production PIC Programmer Windows under US$20
======================================================

1997\12\20@054748 by wwl

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On Fri, 19 Dec 1997 11:43:45 -0200, you wrote:

>I'm developing a battery operated device with 16C71 and I need the 16C71
>to turn the power off. I thought in a transistor controlled by RA4.
>Please take a look in the attached file (just 2K) and say if it's safe.
>Or, does anyone have a better idea?
>
>Regards,
>
>Octavio
>======================================================
>Octavio Nogueira  - e-mail:   KILLspamnogueiraKILLspamspammandic.com.br
>http://www.geocities.com/~oct_nogueira
>"ProPic" Production PIC Programmer Windows under US$20
>======================================================
Why turn it off at all.. ?
Put the CPU in sleep mode, woken by the watchdog or INT interrupt etc.
If you use a micropower 5v reg (e.g. Holtek HT1050 or similar chips
>from Ricoh, Telcom etc.), power when off will be about 5uA (WDT off),
15-20uA (WDT on)., which gives > 20Khours from a PP3/MN1604 battery
(500mAH).

I  saw a neat trick at a seminar recently, using the RC osc, use
OSCOUT to drive a simple charge pump to hold the gate of a supply
switching fet on - doing a sleep instruction turns the supply off.
    ____                                                           ____
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_/ W_/  Hardware & Software design / PCB Design / Consultancy  _/ W_/
/_W_/  Industrial / Computer Peripherals / Hazardous Area      /_W_/

1997\12\23@150809 by Johan Wouters

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part 0 704 bytes
       Alias DarkBob

----------
From:   Octavio Nogueira
Sent:   vrijdag 19 december 1997 14:43
To:     spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU
Subject:        How to turn it off


I'm developing a battery operated device with 16C71 and I need the 16C71
to turn the power off. I thought in a transistor controlled by RA4.
Please take a look in the attached file (just 2K) and say if it's safe.
Or, does anyone have a better idea?

Regards,

Octavio
======================================================
Octavio Nogueira  - e-mail:   TakeThisOuTnogueiraEraseMEspamspam_OUTmandic.com.br
http://www.geocities.com/~oct_nogueira
"ProPic" Production PIC Programmer Windows under US$20
======================================================



1997\12\24@045506 by Octavio Nogueira

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>Why don't you simply use the sleep command? It uses only a few µA.That's
the way we do it in all are batery powered >devices.
>        Alias DarkBob

The problem is I have several op-amps in the same circuit and I need
to turn all off.

Regards,

Octavio
======================================================
Octavio Nogueira  - e-mail:   RemoveMEnogueiraspamTakeThisOuTmandic.com.br
http://www.geocities.com/~oct_nogueira
"ProPic" Production PIC Programmer Windows under US$20
======================================================

1997\12\24@051554 by tjaart

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Octavio Nogueira wrote:
>
> >Why don't you simply use the sleep command? It uses only a few µA.That's
> the way we do it in all are batery powered >devices.
> >        Alias DarkBob
>
> The problem is I have several op-amps in the same circuit and I need
> to turn all off.
>
> Regards,
>
> Octavio
> ======================================================
> Octavio Nogueira  - e-mail:   nogueiraEraseMEspam.....mandic.com.br
> http://www.geocities.com/~oct_nogueira
> "ProPic" Production PIC Programmer Windows under US$20
> ======================================================

Use a 4011 to supply your regulator(s?) and other components that
use unregulated power. You'd battle to even measure the current
and you won't (really) need low-drop regulators because the
circuit is switched off as solid as you can get without a relay.

You can go even further by connecting the 4 NAND gates to form
two 'SR' flip-flops. With these you can let the PIC switch the
whole bangshoot off, and some external input switch it back on
when needed.

--
Friendly Regards

Tjaart van der Walt
EraseMEtjaartspamwasp.co.za
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