ADC Impedance (for reading pots)

[npnick]

Hi. When I use PIC18F I usually use a 10k pot when I want to read a pot value. But now I am using a dspic33f microcontroller and the input impedance is much smaller - 2.5kOhms is maximum recommended for PIC18F, but for the dspic the maximum is only 200ohms! (To minimize the effects of pin leakage currents, it says). I have 6 pots Id like to read, but don't want to consume too much current. Has anyone got any recommendations?

Oh and does it matter if I connect the pot ends to the PIC power supply or the AVdd/AVss pins?

Thanks

 

[duffy]

Just slap a .1uF cap across the input pin and ground, and keep using your 10K pot. They have that low impedance spec because of the charge time on the internal sample cap and the super-high sample rates. For the fraction of a microsecond it samples the pin to the 4.4pF internal DAC cap, the external .1uF cap will show nearly zero impedance.