> It's been forever and a day ago since I read that section, but I thought
> the multiplexer
> specifically discharged the sample & hold capacitor between conversions
> specifically
> to prevent this type of cross talk.
>
> Or is my memory going like my hair?
>
> -Denny

Choosing a random chip
(http://ww1.microchip.com/downloads/en/DeviceDoc/39646c.pdf ) on pdf page
281, there is mention of "discharge" at the end of the ADC cycle, but I
believe this is the discharge of a capacitor array used in a sort of
charge balancing ADC instead of the discharge of the input holding
capacitor. In practice, I designed a DMX lighting controller about 15
years ago. The PIC ADC read slide pots. Each channel also had a "bump
button" that ran the lights to full when the button was pressed. This was
done using a SPDT pushbutton switch. The PIC ADC input connected to the
common terminal of the switch. The NC contact connected to the pot wiper.
The NO terminal connected to +5V. It turned out that these switches had
flakey NC contacts that would sometimes not close. In that case, adjusting
one pot affected the next scanned channel (I scanned down, so pot 13 would
affect light 13 and 12 if the switch on 12 was bad).

So, that's my experience, but I'd like to hear others!

Thanks!

Harold




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