Hi Nick,
I think you may also shield the whole story ( pcb, pot etc ) with an
iron case grounded to a true protective earth.
This will not work if the analogic signal is comming from outside, near
the motor or the motor is driven from the same pcb where you try to
measure the analogic inputs.
In any case you have a nasty problem, integrating via RC the input signal
will slow the system response and add/substarct the noise with the active
signal. Maybe a notch filter or an active low pass filter ? And/or
combined with an average reading methode ?
Tell us the solution which has worked...

regards,
Vasile
http://www.geocities.com/vsurducan


On Mon, 6 Jan 2003, Nick Veys wrote:

> Hello all, I have a project here that will be reading a 0-5V value from a potentiometer on an ADC pin of a PIC16f876.  The problem is there's a nice big (several thousand Watt) electric motor nearby kicking out lots of interference.  I'd like to know if anyone has any common simple methods to minimize the effects of noise and interference.
>
> The pot's will have +5 and ground running to them as well as the signal line coming back out.  Cable lengths will be kept to a minimum but some may be upwards of several feet.  My only basic methods of reducing interference would be a twisted cable and possibly a small capacitor (10's of nF?) at the ADC input pin.
>
> Will a capacitor on the input pin screw things up?  Or smooth things out like I hope. :)  I've only been able to find minimal information on the web about cable twisting, most regarding phone systems or high voltage lines.
>
> Does wire gauge play a role?
>
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