On Tue, 2008-05-06 at 15:31 -0400, John Ferrell wrote:
> Until I fell into the trap I would have agreed with you. The AP Notes 
> regarding ADC are serious reading.
> If you keep the pot onboard with the PIC you can get away with a lot. 
> Reading the wiper of a 5K pot across Vcc and ground is not a problem.
> 
> My Pot is at the end of about 75 feet of cable. The cable contributes some 
> unknown reactance in the configuration. The troublesome noise is a byproduct 
> of the conversion within the PIC.  The current requirements are likely to be 
> damaging to the Pot (500 ohms) if I simply put Vcc across it... I have a 
> 4.3K resistor in series with it.
> 
> The conclusion that I draw at this time is that remote sensing is not a 
> simple matter even if it is just a resistor.

The trick often used for longer sensor runs is actually very simple:
instead of measuring voltage, measure current. By using a current loop
you automatically lower the effects of coupling noise. You also pretty
much remove the wire resistance from the equation.

TTYL
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