AVR-Chat

I can agree with David on this one, I recently used a A2D on a Atmel
ARM7 microcontroller and got really noisy results. Looked at the
analog waveform with my scope and noticed that everytime the A2D did a
sample-and-hold, the voltage dropped by around 0.2V on a 2V signal,
all due to the output impedance of the analog driver. 

Buffering your analog signal could solve that problem ! 

Cheers
Hein B
Auckland, New Zealand.


--- In AVR-Chat@yahoogroups.com, "David VanHorn" <microbrix@...> wrote:
>
> On 6/4/07, Jim Wagner <jim_d_wagner@...> wrote:
> > Some devices allow interrnal pullup to remain on in ADC
> > mode. Check that pullups, etc, are off on those pins.
> 
> That could well be it, or the sourcing impedance is too high on
> whatever is driving the pins.
> There is a certain amount of leakage current possible, that might be
> giving you anomalously high voltages.  IIRC they want the source
> impedance below 10k.
>