Olin Lathrop wrote:

> microsoftwarecontrol wrote:
>
>> But, on my hand, I have plenty of
>> 100k pot and I don't have spare
>> money for "parameter luxury".
>> I did give longer sample time
>> in adc_do();
>
>
> But long sampling time isn't the only problem caused by high source
> impedence.  The leakage current of the A/D input times the impedence 
> causes
> an offset that can't be corrected for by increasing the sampling time.
>
>
> ******************************************************************
> Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
> consultant in 2004 program year.  http://www.embedinc.com/products

Dead right.

Better to use a low impedance method (such as switching the input thru a
MC4066). Otherwise the value measured is often 5-10% off true value.

--Bob
 

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