Benjamin Grant wrote:
> I posted the schematic
> here https://wiki.duke.edu/download/attachments/10715668/Pulsemeter.bmp

While I've certainly seen worse, you need to go back and clean up your
schematic.  Neatness counts whether you think it should or not.  You've got
lines going right thru caps and opamps, redundant part designators,
gratuitous dots in random places, and writing so small as to be nearly
unreadable.  You've already blown your one opportunity to make a good first
impression.  This schematic says "Eh, who cares, good enough for a bunch of
chumps I'm going to ask for free advice.".  And no, I don't want to hear you
blame it on whatever too you are using.  It's your responsibility to both
use the right tool and learn how to use it properly.  It would also be
better if you exported the schematic as a PDF file instead of a image.  That
way we can scale it to actually read some of the text.

As for the circuit:

1 - U is acting like a pure integrator.  It will accumulate any DC offset
from ground indefinitely, including its own offset voltage.  The output of U
won't take long to peg one way and stay that way.  Since that gets used as
the DC level a other U amplifies about, you likely won't get what you
intend.

2 - It looks like OP1 is a photodiode you are trying to use in leakage mode.
That by itself is fine, but I don't see any DC biasing.

3 - I don't see what purpose you think U serves at all.

4 - Q, Q, and Q are NPN transistors with their emitters tied to the positive
rail.  It looks like they are supposed to be PNP.

If you're confused about which U I'm talking about, remember that you gave
them all the same name (duh).


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