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working of knock vibration activated alarm
#1

KNOCK/VIBERATION ACTIVATED ALARM

This inexpensive project can be used as knock / vibration activated burglar alarm. Piezo electric sensor plate can be fixed on table, door, cupboard, window etc using cello tape or adhesive.
When an intruder knocks on them, piezo electric sensor converts mechanical vibrations into electrical vibration.
Electrical pulses are undergone amplification by transistor amplifier stages. Final transistor drives a piezo buzzer.
Time delay can be changed by adjusting value of capacitor connected across 220k resistors. TO activate AC loads buzzer may be replaced with a relay. Load to controlled can be connected via normally opened contacts of the relay.
For demonstration a 9 volts battery can be used.
For continuous use, alarm may be powered using 9 volts or 12 volts AC adaptor. Simple unregulated supply is enough. This alarm can be used to protect car and other vehicles. Other application of this project is an earthquake warning alarm.

Reference: http://seminarsprojects.in/showthread.ph...z4Fsx4CJNe
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#2
Abstract

In this modern world everyone wants something new, something different, so instead of using aswitch to ring the door bell just an alarm is produced by knocking the door which people feelmore luxurious. The circuit of automatic alarm on knocking uses a thin piezoelectric plate,senses the vibration generated on knocking a surface (such as a door or a table) to activate thealarm and can also be used to safeguard motor vehicles. The piezoelectric plate is used as thesensor. It consist IC 555 Timer to which speaker is connected at the output. Piezoelectricmaterial is used at the input in order to convert any mechanical vibration into electrical variation,it avoids false triggering. The plate can be fixed on a door, cash box, cupboard, etc usingadhesive. A 1-1.5m long, shielded wire is connected between the sensor plate and the input of the circuit. A led is placed at the output of the IC 555 Timer. The circuit operates off a 9V or a12V battery.
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#3

Detailed explanation on the working of a earthquake detector alarm with help of a circuit diagram.
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