Vibrating burglar alarm circuit

Published:2014/1/16 21:14:00 Author:lynne | Keyword: Vibrating burglar alarm circuit, | From:SeekIC

The alarms on the doors and windows using a hidden cheap piezo buzzer X1 as a sensor. This piezoelectric buzzer with bidirectional effect: when a voltage at both ends thereof, the piezoelectric ceramic material which will vibrate and produce a sound mechanical deformation; mechanical hand, when it is subjected to vibrations generated thief sound housebreaking When, at its ends will produce a corresponding output voltage. >After the use of a property here, making it play a role in vibration sensor. As shown, the voltage generated by the piezoelectric sensor X1 transistor T1 of the first stage amplifier composed of the discharge is about 100 times. Effect transistor T2 from the detector, its collector voltage is only 50mv. Since R3 directly to the base of T2 being connected to the power line, T2 is always in the ON state can not afford to amplification. If you need to increase the magnification, you can change the upper end of R3 T2 collector received. The transistor T3 provides a voltage gain of about 3 times, and the drive pulse detector D1. When the input pulse level is high enough, T4 rapid charging to C6. After the pulse, C6 slow discharge through a high impedance circuit R9 and R10 and T5 base-emitter composed this discharge time determines the turn-on time of the relay. Therefore C6 capacity required by the test needs to decide its value can select between 1uF-10uF. Piezoelectric sensors X1 should use shielded cable to the input of the circuit Swiss, but the cable should be as short as possible. If radio frequency interference, as shown in dotted lines can be shown between the T1 connected to the base and to add a bypass RFI lnF ceramic capacitors. In use, a known vibration source (such as under normal environmental sounds produced) should be kept away from the sensor in order to avoid false triggering. When the relay is not working, the circuit consumes only a few milliamps. Vibrating burglar alarm circuit shown in Figure:



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