How to Build a FM Intercom

Frequency Modulation, or FM, bands normally are associated with radios, but FM is just the frequency range the device uses to transmit and receive information. Old cordless phones also run on a similar frequency band, which allows them to be used as transmission and reception devices for an intercom.

Things You'll Need

    > Telephone in-line coupler
    > Adjustable wrench
    > Wire cutters
    > Wire stripper
    > Soldering iron
    > 290-ohm resistor
    > 9-volt connector
    > Utility knife
    > Quick adhesive glue
    > 2 used cordless phones
    > 2 used cordless phone bases


Instructions

1.Open a telephone in-line coupler. Hold one end of the coupler with an adjustable wrench and apply downward pressure to the other side of the coupler. The coupler should open in the middle.

2.Cut the middle of the red wire using wire cutters. The red wire is one of four wires inside the coupler. Place a wire stripper on the end of the red wire. Position the teeth of the wire stripper a quarter-inch from the end of the red wire. Squeeze the coating of the wire and pull the coating away from the wire. The internal wire is exposed. Repeat for the opposite end of the red wire.

3.Solder one end of the first red wire to the end of a 290-ohm resistor. Solder the opposite end of the resistor to a 9-volt connector wire. Solder the second red wire to the end of the opposite 9-volt connector wire. A 9-volt connector contains two attachment wires.

4.Cut a quarter-inch hole into the center of the coupler using a utility knife. Insert the excess wire into the inside of the coupler. Pull the 9-volt connector through the hole in the coupler. Glue the center of the coupler using quick adhesive glue and close the coupler.

5.Insert one end of a telephone cord to the right side of the coupler. Insert the opposite end of the telephone cord into the base of the first cordless phone. Insert one end of a different telephone cord into the left side of the coupler. Insert the opposite end of the telephone cord into the base of the second cordless phone.

6.Connect a 9-volt battery to the 9-volt connector. Plug the bases of the cordless phones into an electrical outlet. Press the talk button of the cordless phones to connect the intercom. The coupler connects the two bases to provide communication between them.

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