"David Nebenzahl" wrote in message
s.com...
On 3/27/2009 3:55 PM Tim spake thus:

OK, so I'm trying to come up with a simple (maybe even
elegant) solution to a simple problem. Have an idea I
want to run by y'all.

Function: person has a motion-detector light installed
in their home. They want a buzzer/bell/annunciator of
some kind to go off *momentarily* whenever the light is
activated.

Here's my idea for the circuit:
http://www.geocities.com/bonezphoto/...e-shotBell.gif

OK, so a lot of issues here deal with the AC power being
detected and transferred to something useful. I did a
simple data logger for my well pump (URL:
http://personal.nbnet.nb.ca/snowowl/DataRecorder.html),
that had to deal 220V being sensed. I used a cheap little
cell phone / palm pilot charger that was universal
110/220 50/60hz and wired it parallel with the motor
leads. This gave me a nice 5 volts when the power was
applied to the pump, so I could log it's on cycles. You
still have to wire it up the the light, so that's a
danger here as well. Dealing with AC mains wiring, there
always a need for extra safety.

Thanks for your reply.

Unfortunately, your solution, while interesting, misses
one of the requirements of the whole deal: it needs to
operate the bell/chime/annunciator *momentarily*, not
continuously.

Why not take a crack at calculating the values of the
components and post your final circuit here. That way we
will get a good idea of how adept you are at circuit design.
I would still recommend putting R3 across C2 rather than C1
as per my original suggestion. That insures the drive to the
transistor truly goes to zero after some amount of time.

David