[sdiy] Pots read by microcontroller and sourcing question

[Tom Wiltshire]

An op-amp on each pot is massive overkill in my view. Sorry David!

I second what everyone said about input impedance though - that's the crucial fact. I've used 100K, 47K, 10K and 1K pots all direct into the ADC inputs, all without incident. This is on a PIC, so your mileage may vary on AVR/Arduino. The minimum settling time and maximum accuracy vary with the pot used, but for many applications (reading a knob being twiddled, for example) the uC is so far ahead of the human that it doesn't matter.

HTH,
Tom
 

On 2 Feb 2015, at 19:27, David G Dixon <dixon at mail.ubc.ca> wrote:

>> Hi thanks for the replies.
>> 
>> I'm using an Arduino. Looks like ideal input impedance of 10kb or less
> 
> If you use an opamp buffer in front of every pot, then the output impedance
> to the uC is effectively 0 ohms.  This will cost you about 10 cents per pot,
> so not really a bank-breaker.  I personally would never take a voltage
> directly from a pot for this sort of control, since you really can't
> guarantee linearity unless you feed the pot to a near-infinite impedance
> such as the + input of an opamp.
> 
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