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Basic Alarm Circuit

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Basic Alarm Circuit

Postby Dippel43 » Mon Jan 27, 2014 10:36 pm

I am trying to help a friend build a basic alarm using a diagram he sent me which I believe he found online. It's been awhile since my EE courses in collage but i dusted off the bread board anyway and tried to set it up as shown in the diagram. But something is not correct, it is a simple alarm that is tripped when a ground is broken. Right now, the alarm will go off, but it is supposed to quit after a few moments so as not to drive everyone crazy. I cannot get it to stop unless i reattach the ground. Any ideas? I've attached the schematic to this post.
Attachments
caralarm.jpg
circuit diagram
caralarm.jpg (87.92 KiB) Viewed 5862 times
Dippel43
 
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Re: Basic Alarm Circuit

Postby pebe » Sun Feb 16, 2014 3:19 pm

It appears that T1 stays switched on. I would suspect C1 is connected the wrong way round, or is leaky..
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Re: Basic Alarm Circuit

Postby colin55 » Fri Feb 21, 2014 7:18 pm

Try 1M between base of first transistor and ground
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