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Fixed Frequency Piezoelectric Alarm Circuit

2016-02-20 05:28  
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A common piezoelectric alarm has many valuable attributes. It is compact, lightweight, efficient and reliable. However, the loud, high-pitched sound output can be quite irritating in many applications.The alarm uses a fixed-frequency piezoelectric buzzer in conjunction with the cadmium-sulfide (CDS ) cell and the two-transistor circuit to provide a unique effect. Whenever light reaches the CDS photo-electric cell, the alarm is silent. But when no light strikes the cell, transistor Ql turns on, and the circuit emits a high-pitched tone.The alarm consists of a piezoelectric disk that oscillates at the fixed frequency of 3.137 kHz, created by transistor Q2, A common piezoelectric alarm, such as the Murata (Smyrna, GA) PKB5-3A shown, has many valuable attributes. It is compact, lightweight, efficient and reliable. However, the loud, high-pitched sound output can be quite irritating in many applications.capacitor CI and C2, and resistors Rl through R3. Transistor Ql is used as a switch. It is forward-biased on by R4;-however, the CDS coll turns Ql off when the light is striking it.This circuit uses a thin piezoelectric sensor to sense the vibrations generated by knocking on a surface.

Piezoelectric Alarm Circuit