--- In motm@y..., mark@i... wrote:
> Then it says this circuit generally has "problems with noise and
> instabilities at high frequencies because of the op-amp's high gain
> and internal phase shifts".
Well, how high? 100kHz? 1 mHz? You will be running more or less 1
kHz - 2 kHz tops, so I'd guess you don't even have to worry about it.
Try it on a breadboard, and see if it works.
> Even if I can get the differentiator to work, I would end up with
> both negative and positive voltages. So after this
> differentiatior, I would need an "absolute value circuit"
>
> Do they make comparators that will give a positive output
> regardless of the polarity of the input voltage?
You won't be able to get by with just one differentiator and a
comparator. That's not enough to deal with 3 voltage states - high,
zero, and low. You'll still need the absolute value circuit, OR you
could build a second comparator to trigger on the zero to low
transition, then sum the two comparator outputs. You may also need to
add a one shot to insure that you have a clean output pulse of known
duration.
Moe