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Motion Detector Alrams

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Deepan

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Can you please check this Link out:

**broken link removed**

My question is, why is the circuit build to ignore Ambient light? Is it because ambient light could cause a false alarm in the system?

Thank you for your help.

Dips...
 
The term ambient light is somewhat misleading according to my understanding of the circuit. What they are really doing is using the infared beam as a carrier for a 5KC signal, much like a radio would do. The receiver has a tuned section to pass the 5KC signal to the detector stage. Loss of the signal would trigger an alarm output. If they just used an infared beam without a modulated signal, it is possible to fool the receiver with stray light in the proper frequency range of the detector.
Dialtone
 
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