| 摘要 |
1. An alarm circuit for public prepayment telephone station monitoring system, having a first oscillator (OSC1) the output of which is connected to the primary of a transformer (TR) the secondary of which is respectively connected through two capacitors (C7, C8) to the wires (L1, L2) of the public telephone station line before the connecting contacts (s1, s2) of said station, characterized in that it has a second oscillator (OSC2) the output of which is mounted like the first oscillator (OSC1) output, the first and second oscillators (OSC1, OSC2) being tuned at two different audio frequencies, the circuit also having on the two supply wires of the two oscillators (OSC1, OSC2) two inverter microswitches (PC1, PC2) the condition of which depends on wether or not the cash box is present in the station, those inverter microswitches switching the supply onto the oscillator (OSC2) when the cash box is present and onto the other (OSC1) when the cash box is absent. |
