By modifying the two telephones, short-range communication is possible as long as the ringing circuit is available. A battery string is used to supply power to the two machines, and is connected to the external line through a micro switch. Take the handset and talk to the other party.
Select two telephones (both new and old) as long as the ringing circuit and the call circuit are normal. Repurchase two transformers with a secondary output voltage of 34V to 50V.
Use two self-reset switches to be installed on the two machines A and B respectively. Connect the 34V voltage and connect it to the outside line as shown in the drawing. Then use a battery string and an inductor to supply power to the two units in parallel with the external line. The series inductor mainly prevents the voice signal from being short-circuited by the battery during the call. It can also be connected to the 6V regulated power supply by the power adapter. It is connected to the external line through a micro switch (self-resetting type is installed at the bottom of the earpiece). Pick up the handset during the call and automatically supply power to both A and B. When not in use, the handset is returned to the original position and the two machines are automatically powered off. This circuit is an analog working mode of the telephone line of the telecommunications bureau. When calling, press the ringing circuit button. Take the handset and talk to the other party.
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Post time: Jul-26-2018