Michael Rigby-Jones wrote:

>> I am trying to take an analog signal (out of an MP3 player) and
>> determine its signal amplitude with the PIC's A2D input.  I would like
>> to keep the sampling frequency down (to reduce the clock speed and save
>> power) so I thought of adding a large cap outside the PIC in parallel
>> with a resistor to ground to hold the level.
> 
> Google for "peak detector"

It depends on what you mean by "signal amplitude". If you mean the peak
amplitude, then a peak detector is exactly your thing. If you mean the
equivalent of audible volume in the signal, a peak detector probably won't
give you what you want. In that case you'd need to rectify (small-signal
rectifier) and average (low pass filter) for an approximation.

Gerhard
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