On 3/29/2009 6:43 AM Baron spake thus:

David Nebenzahl wrote:

On 3/28/2009 1:30 PM Baron spake thus:

David Nebenzahl wrote:

On 3/27/2009 3:55 PM Tim spake thus:

In article m,
kens says...

(famous last words, "simple circuit" ...)

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.

I think that a small sugar cube relay, diode, resistor and capacitor
will do the job !

Circuit, pleeze?

Ok but excuse the ascii art.

live ----diode---relay---resistor---capacitor---neutral

You're excused. That illustrates the circuit perfectly.

Size the resistor to give the time constant with a particular value
capacitor. The relay contacts are isolated and can be connected to
your low voltage circuit.

The resistor should have sufficient wattage rating with respect to the
current and the capacitor should be rated for at least the maximum
voltage applied. ie 120v X 1.414. The relay can be almost anything
with a suitable coil voltage. ie 100 - 120.

The circuit works by utilising the charging current into the capacitor
to energise the relay. As the capacitor voltage increases the relay
will drop out. The time difference between energising and dropping out
is how long the annunciator will sound.

So I take it you'd like this circuit:
http://www.geocities.com/bonezphoto/...-shotBell2.gif

And now can you give us the R and C values to give, say, a 1- or
2-second on time? I don't know how to calculate such things. (Understand
how they work, just never learned the actual math involved.)


--
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Made With Pears: Pretty good chance that pears will be detectable in
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(with apologies to Dorothy L. Sayers)