The described device protects the telephone line of a subscriber from unauthorized connection "pirate" of the device.
In the proposed blocker applied some schematics contained in the materials published in "Radio" earlier [1, 2].
The lock is easy to manufacture, requires no additional power. It is supplied from the telephone network. Current consumption - no more than 160 μa. The device is assembled on the shared elements, does not require setting.
Connect the lock to break the telephone line at the entrance to the apartment, observing the polarity. When the handset is on the phone, the line voltage is 60 V, in this case, through the Zener diode VD4 in the base of transistor VT2 current flows. The transistor VT2 open. When hook line voltage drops to 5... 15 V Zener diode VD4 is closed. If the tube has been withdrawn by the owner with the phone connected after lock, opens the transistor VT1, collector current which supports when open, the transistor VT2. On his header and the control input the switch SW1 is low. The key is closed, and bypass the phone lines 's going on.
If connected to "pirate" the phone (before the lock), tension in the line falls, the transistor VT2 is closed, the transistor VT1 and a Zener diode VD4 closed. The capacitor C3 is charged through the circuit VD1, DA1, VD3, R3, R5, key K1 opens and bypasses the resistor R2 of blood. Dialing a "pirate" phone becomes impossible.
The current stabilizer DA1, Zener diode VD2 and capacitor C1 provide nutrition (3 In) of the transistor VT2 and chains IN R5C3 moments-circuit dialer "pirate" phone capacitor C2 provides recharge of the capacitor C3, and diode VD3 prevents the discharge of capacitor C2 through the Zener diode VD2.
The device incorporates capacitors: C1 and C2 - C50-16, C3 - km-6. Zener diode VD4 can be replaced by SI, XI, SI.
The device is assembled hinged mounting on the circuit Board sizes 21x41 mm.
The described device is not certified, so it can apply only as part of the office PBX and on the lines, which has no outlet in telephone network of General use. To improve the reliability of the device recommend the emitter-base of transistor VT2 shall be shorted resistor 1 MOhm.
Literature
Author: V. Davidenko, St. Petersburg