Re: Help with normally closed relay on motion sensor

On Fri, 28 Sep 2007 22:05:37 -0700, Elephant <drw41@xxxxxxx> wrote:

I have a motion sensor that has a normally closed relay. When motion is
detected, the relay opens. There is no option for a normally open
connection.

If I hook the contacts up to a buzzer, the buzzer of course will sound
all the time unil motion is detected.

What would be the best way to get around this. Another relay, an
opto-isolator.........??????

Any help would be appriciated. Don't want to have to construct too
complicated circuit.

There is no best way, but better ways shade into more complicated
solutions. A straightforward approach is to use a second relay with
the opposite sense such that, when it is powered through the motion
detector relay it will hold its contacts open. When the motion
detector fires, its relay contacts open, allowing the second relay
contacts to shut, powering the buzzer.



.----------------------.
battery or | | |
other source | | |
--- | |
- | |
| | |
| | | .-----.
=== | | | |
GND / \ | |
.----. o o .-----_ o o | .-.
| |----- )| | )| | ( X )
| | )| | )| | '-'
| |----- )| | .-_)| | |
'----' '-------' | '-----' |
| |
=== ===
GND GND

sensor NO relay NC relay alarm/buzzer
"on" = shut "on" = open
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
.

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