[sdiy] Pots read by microcontroller and sourcing question

[Jack Jackson]

Hi thanks for the replies.

I'm using an Arduino. Looks like ideal input impedance of 10kb or less

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> Date: Mon, 2 Feb 2015 14:39:05 +0100
> From: modular at go2.pl
> To: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Pots read by microcontroller and sourcing question
>
> 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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