A simple intercom made from a pair of old corded telephones

Do you have a couple of old telephones lying around in your closet? - There is no need to throw them away - make a very simple intercom out of them - an intercom. With it you can establish wired communications over hundreds and even thousands of meters. Everything is free and no roaming.
At one time, my friend and I installed such an intercom between apartments, and wires were routed through the windows. And even now this has not lost its relevance: you can establish a constant connection with a summer house in the garden, with a bathhouse, with a neighboring house, etc. This is also a great toy for children.

Will need

• Two telephones - any: push-button, rotary, the oldest Soviet or the newest foreign.
  
• Wires for connecting phones to each other. If the device is connected through a socket, the wires must have connectors at the end.
  
• Battery 9 V crown type.
  
• 300 Ohm resistor (+/- 10% if this is not the case).
  
• Electrical tape or heat shrink.

Tool:

How to connect phones and make an intercom - intercom

Everything is very simple to the point of banality! You just need to connect all the elements in series: telephone sets, battery, resistor. Polarity is not important.
For reference: The usual modes of the telephone network are such that at the moment of rest there is a voltage of 60 V in the network, at the time of a call - 180 V and at the time of a conversation about 9 V. So we will use a battery to create a potential of 9 V in the circuit between the devices.
Let's take the wire connecting the phones and cut one of the two and make a branch.

We connect a resistor and a battery in series into the gap. All! The intercom is ready.

Let's check. If everything is good, solder everything permanently and insulate it with heat shrink.

Next, it is advisable to place everything in the case. Having previously made slots in it for the wires.


As a result, the intercom looks like:

Checking the work:

The audibility is excellent: clear, without jumps or “drops”, generally ideal.
Now you can extend the wire to any distance. It is not necessary to disconnect the battery - if both tubes are in position, the current consumption is almost zero.
But if you don't have a crown, take a regular 9 V adapter.

Or 12-15 V, but in this case you will need to make a step-down converter according to the scheme:

We assemble and insulate with heat shrink.

Now, if you need to make a conversation with a subscriber, turn the unit on to the network and talk.

Watch the video