Switching circuit for telephone set - changes hand-crank generated 50 hz signal over to 25 hz frequency used in set, which is then used for both systems

摘要

The changeover circuit changes the e.g. 50 Hz frequency of a ringing signal, generated manually by a hand-crank over to the e.g. 25Hz frequency that is usually used in telephone sets and thereby allows the same set to be used for either of the two systems. A pushbutton (T) connects a control circuit (T1-T3) to the output of the cranked generator (1). The control circuit drives a relay (R) whose two changeover contacts (r1, r2) connect the generator's output to the changeover circuit's output (A).