How to make an Intercom using telephone cables
An intercom (intercommunication device), talkback or doorphone is a stand-alone voice communications system for use within a building or small collection of buildings, functioning independently of the public telephone network. Intercoms are generally mounted permanently in buildings and vehicles. Intercoms can incorporate connections to public address loudspeaker systems, walkie talkies, telephones, and to other intercom systems. Some intercom systems incorporate control of devices such as signal lights and door latches

Step 1: Materials

Things you will need:

1) 12-30VDC volt power supply (Can be a standard battery or transformer plugged into an AC outlet) (Confirmed 4 9-volts will work

2) 300 ohm resistor (Less than a $1 at 99% of radioshacks)

3) Minimum 2 wire telephone cable

4) Wire Strippers

5) Two or more telephones

6) Electrical Tape

Step 2: Procedure

How to make an Intercom using telephone cables
Process:

Take the telephone cable and somewhere along the line strip the covering down to the 2 small cables (most likely red and green).

THE GREEN/WHITE WITH BLUE STRIPE SHOULD NEVER BE ALTERED IN ANY WAY

In that location, cut the red(or blue w/white stripe) wire in half

For the next steps you might want to have 2-3 inches of wire spare around or cut it from red of the telephone cable

Strip the red wire on both sides where you just cut

Completed Diagram/Schematics6Attach one side of the red wire to one terminal of the power supply (Polarity does not matter)

Take the 2-3 inches of wire and connect the other power supply terminal to one end of the resistor

Attach the other side of the cut red wire to the other end of the resistor.

Plug any form of telephone into each plug at each end of the telephone cable

Presuming everything is done correctly, one person on each end should now be able to communicate with each other

Step 3: Tips

How to make an Intercom using telephone cables
Do minimal stripping and always cover the connections with ELECTRICAL Tape

Step 4: Warnings

THE GREEN/WHITE WITH BLUE STRIPE SHOULD NEVER BE ALTERED IN ANY WAY

The ringer will not work (The ringer is a 90-volt AC wave at 20 hertz)
 
 

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