AVR-Chat

Richard Cooke Wrote
>I'm trying to minimize current consumption and I'm using the internal
>1.1V reference so I'm using a voltage divider 1M + 3M to bring the
>signal down to below the 1.1V reference.  I don't care how long the
>conversion takes as I'm only making the measurement every 10 minutes
>or so.
>
>Do I need to use a buffer between the divider and the input to the
>ADC?  

I would expect so.

>If I do, what small, cheap and low power chip would you recommend?

A 0.1 uF capacitor.  Although you will need to sample faster than once
every 10 minutes to avoid aliasing issues.  The capacitor will act as a
local charge buffer and the charge taken from/added to it by the s/h
capacitor will be small enough not to be noticeable.  It will also act as a
low pass filter, just not long enough to deal with a 10 minute sampling
period.

Robert


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