'Running a pic at 3.3 volts and peripherals at 5 vo'
William K. Borsum
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
Anyone done this? And did it work? (without a lot of level shifting)
William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems
<dascor.com> & < borsumhttp://www.dascor.com>San Diego, California, USA
Juan Pablo AGUIAR
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
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.
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
De: William K. Borsum <DASCOR.COM> borsum
Para: MITVMA.MIT.EDU < PICLISTMITVMA.MIT.EDU> PICLIST
Fecha: Lunes, 20 de Diciembre de 1999 11:19 a.m.
Asunto: Running a pic at 3.3 volts and peripherals at 5 volts
With clamping diodes you would expect battery charging from high input level
via limiting resistor ;)
I prefer this simple circuit:
| | PIC
any diod |
Input low level voltage must be low enough to compensate for diod voltage
Good thing is that the circuit doesn't draw current when input level is
Nikolai Golovchenko, Electrical Engineering Student
National Mining University of Ukraine http://www.nmuu.dp.ua
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