alarm clock question

Feb 21, 2010 2 Replies

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Jon 16 years ago

I have a digital alarm clock. I want to wire the alarm signal to activate a fire bell. The fire bell is 120vac @ 40mA. The alarm signal from the clock is around 1.5 vdc.

I found a connection on the alarm clock that is 7.5 vdc all the time.

I have 5vdc relays with contacts rated for 6 amps. I have some 5vdc reed relays. None of them work for the 1.5 vdc alarm signal. I tried messing with some transistors but I don't know enough about them to rig something up. I have a bunch of resistors and capacitors.

I have a second alarm clock where the alarm is connected to a small speaker. I'd like the fire alarm to go off when the speaker beeps a signal or when the radio alarm goes off.

Any suggestions?

Jon

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Jan Panteltje 16 years ago

On a sunny day (Sun, 21 Feb 2010 12:20:41 -0500) it happened "Jon" wrote in :

7.5 V --| |---| |------------------- |/| |/| | | | Si doides | | | -------- bell ---- | --- | | | === / \ | o | --- --- [ \ ] | 120V AC |100uF | | o | | |------- | | | b |/ c ------------------

1.5V DC --- R 1500 ---)---- | NPN relay | |\\ e 5V | | GND ----------------------

Something like this perhaps?

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Jon 16 years ago

Thank you Jan. Using your help I wired the transistor in and my fire alarm clock works! I used a capacitor and two resistors, no diodes, and a transistor. Jon

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