The scheme is simple electronic guard device published the magazine “Funkamateur” (GDR). Across the doors of the protected object stretched thin wire. Until he is whole, the tension on the bases of the transistors VT1—VT3 are few and they are closed. In case of wire break on VT1 through a resistor R2 receives the bias voltage, and this semiconductor device is opened. Now, through a chain of R2—R4, the transistor VT3 will get more offset. Relay K1 will work, and its contact system will include a siren, a buzzer or a lamp. Moreover, the elimination of wire break will not change the situation is to disable the watchdog is possible only with the switch ЅА1.
The device can be applied to domestic transistors series КТ342, KT315 (VT1), KT361, КТ203 (VT2) with h 21E> 100. The type of transistor VТЗ selected depending on current of the relay K1, for example a series КТ603, KT315. The diode VD1 — D226 with any alphabetic index.
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