Re: Help needed designing simple circuit

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 <49c944ff$0$29984$822641b3@xxxxxxxxxxxxxxxxxxxxxxxx>,
nobody@xxxxxxxxxxxxxxx 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

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.

--
Best Regards:
Baron.
.

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