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'Running a pic at 3.3 volts and peripherals at 5 vo'
1999\12\20@140821 by William K. Borsum

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Hi all:

Has anyone had any experience running a Maxim MAX 186 or similar ADC at 5
volts while talking to a PIC running at 3.3?

I'm running into some power issues where I would like to keep the analog
side at 5 volts, but the PIC side and all the memory and logic running at
3.3 volts.

Anyone done this?   And did it work? (without a lot of level shifting)

Kelly

William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems
<spam_OUTborsumTakeThisOuTspamdascor.com> & <http://www.dascor.com>San Diego, California, USA

1999\12\21@080708 by Juan Pablo AGUIAR

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I have made a radio control receiver using a pic at 5 Volt. the input to
the pic is a digital signal of 0 to 8 volts. I used a resistor between
both. With out the resistor pic works fine, also.

At the transmiter, Pic is running with 2 AAA bateries (3 Volt) and the
radio oscillator running with a 12 Volt battery. I noted great energy
saving if PIC is running at low voltages.

Juan Pablo Aguiar

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1999\12\21@160506 by Erik Reikes

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At 09:44 AM 12/21/99 -0300, you wrote:
>I have made a radio control receiver using a pic at 5 Volt. the input to
>the pic is a digital signal of 0 to 8 volts. I used a resistor between
>both. With out the resistor pic works fine, also.
>
>At the transmiter, Pic is running with 2 AAA bateries (3 Volt) and the
>radio oscillator running with a 12 Volt battery. I noted great energy
>saving if PIC is running at low voltages.

I would recommend current limiting resistors and clamping diodes.

With just the resistors you are using the internal clamping diodes of the
PIC, which I hear is a no-no.
Also, be sure the any external logic you are interfaceing with allows logic
highs way below 3.3 (I'd recommend 2.2 or so.).

There are some inverter/buffer chips that are good at this sort of thing.


-Erik Reikes

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1999\12\23@105329 by felix centeno

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I had used the MAX1240 , this is a A/D conveter with Vcc=3.3 V
I put tree 1N4001 diodes to supply and the PIC know that over
3 Volts is ONE , all the other circuits were Vcc=5V

-----Mensaje original-----
De: William K. Borsum <KILLspamborsumKILLspamspamDASCOR.COM>
Para: RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU <spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU>
Fecha: Lunes, 20 de Diciembre de 1999 11:19 a.m.
Asunto: Running a pic at 3.3 volts and peripherals at 5 volts


{Quote hidden}

1999\12\27@234834 by Nikolai Golovchenko

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{Quote hidden}

With clamping diodes you would expect battery charging from high input level
via limiting resistor ;)


I prefer this simple circuit:

            + +Vdd
            |
            \
     51k    /
            \     ----
            |     |  PIC
 +----|<----+-----|
     any diod     |
                  ---


Input low level voltage must be low enough to compensate for diod voltage
drop.
Good thing is that the circuit doesn't draw current when input level is
high.


_

Nikolai Golovchenko, Electrical Engineering Student
National Mining University of Ukraine http://www.nmuu.dp.ua
Dnepropetrovsk, Ukraine
E-mail: RemoveMEgolovchenkospamTakeThisOuTmail.ru

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