Dual device that can perform both telephone control and power reset

The circuit diagram of the device is shown below. Its control switch is located in the broadcast control room at the bottom of the mountain, and the rest of the settings are located in the radio room on the top of the mountain. J is a 5v relay, and its normally closed contact is connected to the working power supply (AC220V) of the logic controller. When the switch in the room at the bottom of the mountain is turned to the short-circuit end (reset), the b-pole of transistor T1 is turned on by adding a positive potential through the switch, relay J is energized, and the normally closed contact is disconnected, that is, the 220V power supply of the logic controller is disconnected. When the switch in the room at the bottom of the mountain is turned back, the b-pole of transistor T1 loses the positive potential and is cut off, so that relay J is released and the reset process is completed, thus avoiding the need for personnel to go to the room on the top of the mountain to operate. The internal telephone is connected to the business copper wire through the other end of the switch in the room at the bottom of the mountain, and connected to the telephone in the room on the top of the mountain, so that when the reset operation is not performed, the communication between the telephones on the top of the mountain and the bottom of the mountain is normal.

Diodes D2 and D3 are used to isolate the voltage of about +25V on the telephone line from the ringing voltage of about 90V. D4-D9, D10-D15 are two sets of diodes connected in series and then connected in reverse parallel to ensure that the telephone will not misoperate the reset circuit under various circumstances. Resistor R- is generally a few hundred ohms. It is connected in series with the line resistance to form a current limiting resistor. Its value should ensure that when performing the reset operation, relay J can be reliably attracted.

Line connection

The business line sent down from the transmitter room on the mountain has a voltage value of about +3.8V at both ends. The positive end is in the switch connection and must be on the same terminal as the positive end of about +25V sent from the telephone switchboard to ensure normal operation.