| 摘要 |
PURPOSE:To avoid the time when communication is impossible, after the transmission of the push-button signal with suitable amplitude as the side tone, by controlling the side tone to the operator of the trunk board with the light emitting element given to the push button signal transmission circuit. CONSTITUTION:The control circuit 1 monitors whether or not the trunk board 2 has the request to deliver the push-button signal or not, and if request is present, the push-button signal transmission circuit 4 is controlled to deliver the push-button signal, and the light detection element 15 is operative through the operation of the light emitting element 16. When the photo detection element 15 is operated, the transistor 10 is non-conductive, and the push-button signal is transmitted to the communication path switch 5 and delivered to the trunk board 2 with attenuation due to the resistor 11 and capacitor 12. On the other hand, while the push button signal is not delivered, the base current flows via the resistors 14, 13, the transistor 10 is conductive and the communication current to the trunk board 2 is supplied. |
