Burglar Alarm Circuit

Published:2011/5/10 0:43:00 Author:chopper | Keyword: Burglar Alarm | From:SeekIC

As is shown in figure is a burglar alarm circuit. Detection circuit in the figure adopts resistance bridge and the switch of door adopts magnetic operation switch.The switch will be conducted when door closes while it will be stoped when door opens.The switch and a resistor of electrical bridge form a arm of the electrical bridge,which is set up in the hovel.Thus, if the door is unclenched,the magnetic operation switch will stop;And if exterior line is short or disconnective,in both cases,the bridge circuit will lose balance.The voltage of A、B through rectifier bridge 1N4148 makes optical-coupler run,therefor makes bidirectional thyristor connected and then the bell sends out a alarm.We get supply voltage through the process of voltage reduction by capacitor, half-wave rectification and voltage stabilization by 18V stabilivolt.The switch of door can adopt a magnetic operation switch which is always on as well as microswitch or micro-button.One resistor of the bridge-arms must be set up with the switch.Cut off the power when it needs not to give an alarm,or it will ring even if you yourself opens the door.



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