[sdiy] Pots read by microcontroller and sourcing question

[Roman Sowa]

It all depends on what ADC requires in terms of input impedance. The ADC 
input has some capacitance, and it must be fully charged before it 
starts conversion during fixed, very short acquisition time. It should 
be clearly stated in the datasheet.
However, if you only need lower resolution, like for example 7 bits for 
MIDI in 10-bit ADC, you don't care for 1LSB accuracy in 10 bits. So it 
is still safe to use higher impedance source, that small error is 
smaller than 7-bit LSB.

Of course you can always add an OPAMP working as a buffer, but then you 
have more parasitic capacitance still in the circuit covering all pots. 
That limits your maximum scan rate. The voltage from potentiometer must 
change between scans from one pot to another, and with 100k it will take 
longer to settle.

Another issue is sensitivity to interference. Just like with a 
microphone. Longer wires from pot to ADC - more prone to pickup hum. 10k 
pot will be less sensitive than 100k.

Roman

W dniu 2015-02-02 o 14:04, Jack Jackson pisze:
> Hi all,
>
> Is there any difference in operation when using a 10Kb potentiometer
> into an ADC instead of a 100Kb?
>
> Also any source out there for 9mm ALPs pots with a centre detent?
> also 9mm ALPS with 4 detents?
>
> Best Regards, Jack _______________________________________________
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