Automatic Door Bell Ringer Project Multisim

Circuit Operation

The IR LED and the phototransistor is placed near such that, in normal operation, the phototransistor doesn’t receive any light and doesn’t conduct. Thus, the transistor (as it doesn’t get any input voltage) doesn’t conduct.

Since the timer input pin 2 is at the logic high signal, it is not triggered and the buzzer doesn’t ring, as it doesn’t receive any input signal. If a person approaches the door, the light emitted by the LED is received by that person and gets reflected back. The phototransistor receives this reflected light and then starts conducting.

As this phototransistor conducts, the transistor gets biased and starts conducting too. Pin 2 of the timer receives a low logic signal and the timer gets triggered. As this timer gets triggered, a high logic pulse of 9V is generated at the output, and when the buzzer receives this pulse, it gets triggered and starts ringing.
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Видео Automatic Door Bell Ringer Project Multisim канала LabVIEW & MULTISIM