Device for connecting several telephone sets to one telephone line

摘要

In an automatic changeover switch, several telephone sets F1 to F4 can be connected in each case via first switching elements 16, 30, 31, 32 to loop current detection circuits S1 to S4, on the one hand, and directly to the telephone line 11, on the other hand. The telephone line 11, in contrast, can be connected in parallel via a second switching element 13 to the inputs of the loop current detection circuits. When a loop current occurs, the latter generate a control signal 21, 39, 40, 41 and 43 so that the second switching element is always reset jointly with one of the first switching elements. As soon as one of the control signals is generated as the receiver is taken off the hook on one of the sets F1 to F4, this results in a disconnection of all paths via S1 and S4 to the sets F1 to F4. It is only the set which was first activated which is still connected directly to the telephone line 11 via its associated first switching element. The remaining sets can therefore not be activated as long as the connection to the first one exists. In consequence of the parallel branching and the effect of each of the first switching elements which is limited to the respective branch, more than two telephone sets can be connected without great expenditure. <IMAGE>