Telephone line burglar alarm circuit diagram

Phone alarm device can monitor and prevent unlawful misappropriation of your telephone line. When someone in your telephone line and the machine thefts from outside the alarm on the issue of interference signals, so thieves can not dial, and the light was stolen
Telephone line burglar alarm circuit diagram - schematic

phone to the owner Tip Sound. The following figure is a schematic diagram of the anti-theft device, usually the post office sends program-controlled machine outside line standby voltage of about 60V, the D1-D4 is positive polarity switch on top, D5 breakdown by R2 enable T1 base potential rises, T1 guide pass, T2 cutoff, T3 is turned off, the oscillation circuit consists of T4, T5 composition does not work. When the phone theft elevator, outside the voltage drop of about 9V, can not make D5 breakdown, T1 because no bias cut, T2 base potential rise conduction. T2 is turned on so T3 is turned on and driven by the audio-stage oscillation circuit, LED, DY audible alarm, and through the LED, DY interfering signal plus an outside line, while the external voltage is low, so that person can not be stolen phone dial-up and forced to hang up. Although the owner pick up the phone to reduce the voltage, and T1 is turned off but the T6 or T7 (with T6, T7 two tubes for ease of installation, the line can access, regardless of polarity, D6, D7 isolators) by telephone machine to obtain the base current conduction, the T3 is not conducting an oscillation circuit does not work. Therefore, the owner can dial the normal call is not affected. Because then there is only a very small resistance value between the master telephone with an outside R8, R9 so that when the phone call zero vibration are not affected. Telephone line burglar alarm circuit diagram Selection of electronic components D1-D4, D6, D7 can be used as general IN4007 rectifier, etc., D5 choice about 18V regulator, DY is 3V electromagnetic buzzer. Resistance can be used carbon film resistor 1 / 8W, and other elements of the model shown in the illustration selected.

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