twin bell-push

1111.411104111 It is often desirable for a single door- bell to be operated by two bell- pushes, for instance, one at the front door and the other at the back-door. The additional bell-push, S2, in series with the break contact of relay Re1, is connected in parallel with the original bell-push, Si. When S2 is pressed, the bell voltage is rectified by D1and smoothed by C1. After a time T = R1R2C2, the direct voltage across C2 has risen to a level where T1 switches on. Relay Refis then energized and its contact breaks the circuit of S2, so that the bell stops ringing. After a short time, C1and C2 are discharged, the relay returns to its quiescent state, and the bell rings again. In this way, Si will cause the bell to ring continuously, while S2 makes it ring in short bursts, so that it is immediately clear which bell-push is operated. S2 twin bell-push Tr1 = bell transformer elektor july/august 1985