This is a simple design circuit for shock sensitive alarm circuit that has many applications fro home to automobiles. The main application of this circuit is to use it as an anti theft alarm in automobiles. A peizo electric sensor is used as the shock sensor which has to mounted on the door which you have to protect. This is the figure of the circuit.
The operation of the circuit is based on the LM358 as the controller. The IC1 LM 3558 is wired as an inverting Schmitt Trigger. The POT R1 sets the threshold voltage of the circuit.R1 is used as a feed back resistor. When not activated the out put from the piezo sensor will be low and so do the output of the IC. When the piezo sensor is activated its output voltage goes high and triggers the Schmitt trigger. This results the beeping of the buzzer. The buzzer remains beeping for some time even if the vibration is removed. This is because the increase in the inverting input has little effect when the IC is triggered and the state can’t be easily reversed. Fix the sensor firmly to the surface, where ever you place it. It is always good to place the sensor near to the door knob. The circuit is powered by a 3 V battery can be used as power supply. Adjust R2 to obtain the required sensitivity.
The operation of the circuit is based on the LM358 as the controller. The IC1 LM 3558 is wired as an inverting Schmitt Trigger. The POT R1 sets the threshold voltage of the circuit.R1 is used as a feed back resistor. When not activated the out put from the piezo sensor will be low and so do the output of the IC. When the piezo sensor is activated its output voltage goes high and triggers the Schmitt trigger. This results the beeping of the buzzer. The buzzer remains beeping for some time even if the vibration is removed. This is because the increase in the inverting input has little effect when the IC is triggered and the state can’t be easily reversed. Fix the sensor firmly to the surface, where ever you place it. It is always good to place the sensor near to the door knob. The circuit is powered by a 3 V battery can be used as power supply. Adjust R2 to obtain the required sensitivity.
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