Roy J. Gromlich wrote:
> This is just a guess, but I think he wants to digitize the 50KHz
> signal and do some processing on it.  Unfortunately, the rule of
> thumb for signal processing says that you need to digitize at least
> 2X your highest frequency of interest (100K samples/sec).

This is not just a "rule of thumb", but a hard theorectical limitation.  The
2x frequency is also called the "Nyquist rate".  In practise, you *need* to
sample at least a little faster than the Nyquist rate.  This is because in
reality there is no filter that has a totally sharp cutoff.  Most of the
time you will need to sample at least 4x the maximum frequency of interest,
although even that will require a reasonably decent digital filter.

> The A/D converter is not going to run at
> 250K samples/sec. --- you need an external chip to do that. But
> that's not a big deal:
> 12-bit 1MegaSamples/sec chips are readily available and are pretty
> cheap, even.

Or use a dsPIC with 12 bit 500K sample/sec A/D.  Check out the 30F2010,
which is also the first dsPIC to become available.


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