This man-made product does not claim originality, but the no less really works, unlike schemes on one relay.
The scheme consists of an analysis of the condition of the tube (connected to the AVU L1 and L2) and transducer ringing (Conn. to AVU Zv). The analyzer tube status configurable podstroechnik (upper circuit) so that the output appropriate logic element, when answered was a log. "0". Must be set to zero at the output persisted in set rooms.
The sensor of the call consists of a pulse shaper(lower left element) and the delay element, his task is to ensure that it did not work on "the bells" when raising and lowering the tube, only when you call and set rooms (setting respectively the second podstroechnik).
On the logic of the scheme is clear, through the element And combining the two sensor, enabled via the relay transistor (I RES). On the second transistor assembled circuit protection of the phone, disconnecting the call signal, when lifting the handset. For the operation of the circuit requires a power supply 9-15V and the power source for the call, (~60V breaks) I have a transformer with windings 10 and 60 V.
When reprinting, please do not throw me out of the list of authors.
Author: Victor Naumov; Publication: N. Bolshakov, rf.atnn.ru