How To Build An Intercom For Your Small Business Using 2 Old Cordless Phones

Small business owners are very cautious about their company's expenses, keeping them as low as possible. One way you can control your business' expenses is to build an intercom system yourself, instead of buying an expensive telephone system with intercom capabilities. Keep reading to learn how to turn 2 average cordless phones into an intercom system that you and your employees will find invaluable:

Materials Needed For This Project:

  • 2 Cordless telephones

  • 2 Telephone cords (CAT 1 cable)

  • 9-Volt connector

  • In-line coupler

  • Dremel

  • 265 - 300 Ohm resistor

  • Soldering iron

  • Solder

  • Wire cutters

  • Electrical tape

  • Helper

Step 1: Open the in-line coupler to access the wires.

Use your hands to open the in-line coupler by applying pressure to the center and separating the two sides. If you have to, press it against the table or your desk to crack it open. Once the coupler is opened, you will see red, yellow, black, and green wires. You only need to be concerned with the red and green wires for this project. The other wires are for the second telephone line and are not needed.

Step 2: Cut, and strip the wires.

Use your wire cutters and snip the red wire in the middle. Now you have 2 red wires, one on each side of the coupler. Strip the insulation off the ends of both red wires.

Step 3: Solder the wires, resistor, and 9-volt connector.

Take the end of one of the red wires and solder it to one side of the resistor. Solder one end of the 9-volt battery connector to the other end of the resistor. It doesn't matter which end of the 9-volt connector you solder the resistor to. Now, connect the other red wire to the empty side of the 9-volt battery connector.

NOTE: all of these wires need to fit back into the coupler when the project is done, so it's a good idea to trim off excess wires from the 9-volt connector and resistor before you solder them. Since you don't need the yellow and black wires at all, you can cut them off completely.

Step 4: Put it together.

With the coupler still open, plug a cordless phone into one end of the coupler. Then plug the second phone into the other side of the coupler. Now plug in the 9-volt battery. Make sure the cordless phones are charged before moving on to the next step.

Step 5: Test the connections.

Grab a helper to test your new intercom system. Simply push the power button on both phones. One person should talk into their phone while the other person listens. If the intercom works, proceed to Step 6. If it doesn't work, skip to Step 7.

Step 6: Seal the coupler.

Once you've verified that your new business intercom system works, seal any exposed wires with electrical tape. Use a Dremel to drill a small hole into one side of the coupler to allow the 9-volt battery connector wires to come through when it's closed. Being careful not to break any of the soldering you did in Step 3, close the coupler with the 9-volt connector leads coming out of the hole you drilled.

Note: if you'd like your new intercom system to ring, you'll need to purchase a ring generator.

Step 7: Troubleshooting

If your new homemade intercom system isn't working, here are some troubleshooting tips:

Verify the phone cable works: Replace the cable on a working phone with the cable you're using on your intercom. If the phone doesn't work after switching cables, it means there is a problem with the cable. Use a new cable on your intercom.

Verify both phones work: Replace a working phone with one of the cordless phones you're using for your intercom system. If you hear a dial tone, the phone is working. Check the other cordless phone in the same manner to ensure it's working.

Verify the coupler is making a circuit: Take out the coupler's battery. Then go to your nearest working telephone and make connections in this order: wall jack connected to cable, connected to the coupler, connected to another cable, connected to the phone. If you hear a dial tone then you either have a short in the coupler or you soldered the wrong wires together. If you hear scratching sounds when you move the coupler, then there's a bad connection and you need to re-solder the wires or insulate them better. If you don't hear anything, that's good. Use a screwdriver to complete the circuit at the 9-volt battery connector. If you hear a dial tone, that's good. If not, then you have a broken connection on the red or green wires and you need to find it and fix it.