| 摘要 |
PURPOSE:To adapt a public telephone set with simple constitution to various control systems, such as telephone set control and switchboard control, by preventing toll origination corresponding to different kinds of switchboards by selecting respective talking circuits, etc., according to combinations of change-over switches of contacts of relays for monitoring polarity inverted signals. CONSTITUTION:The circuit of L1, R3, D1, ZD1, D5, L2, etc., making a dial-in pulse contact with a momentarily polarity-inverted signal from a station before a called subscriber answers and the other circuit of L1, D9, HS, T, R7, and L2 forming a high impedance loop for the momentarily polarity-inverted signal are provided. Further, the circuit of L2, R1, Q1, VSS, D3, R3, and L1 forming a calling loop by a polarity-inverted signal generated by the answer of the called subscriber is formed. Furthermore, switches SW1-SW4 operated according to the kind of a connected exchange, and contacts rl1-rl2 of a relay RL for monitoring polarity-inverted signals under the control of those switches SW1-SW4 are provided. Then, each circuit is selected according to the combination of switches SW1-SW4 and contacts rl1-rl2 to adapt the public telephone set to different kinds of control. |
