MOTM

At 4:31 PM +0000 03/12/01, mate_stubb@... 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.

Good point!!

>> 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.

Hmmmm...using two comparators might be less parts.  Do they make
comparators that can be configured to detect negative or positive
voltages??  That way I can get two (or more) of the same kind one chip.  I
also wonder how I can connect output of the same differentiator to two
different comparators without having them interfere with each other.

I'm starting to think that Horowitz & Hill might not be the best book for
me.  I need something entitled _Comparators for Dummies_ or _So You Want to
Use a Comparator??_  :)

Are there any comparators whose application notes you would recommend??

>You may also need to add a one shot to insure that you have a clean
>output pulse of known duration.

OK :)  I know how to build one with a 555 if I find that's necessary.