Build your own intercom or walkie talkie out of two old cordless phones

We all have old phones. Why not turn them into an intercom for your kids tree house. Or turn two old cordless phones into home base walkie talkie. Here is how.
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Step 1: Materials

In-Line coupler (I got mine at Frys for 1.49)
9 volt connector (radio shack, or cut it out of some old piece of junk)
milk (helps keep you hydrated and keeps bones strong)
Soldering iron
300 ohm resistor or close to it
black electrical tape
two telephones
two telephone cords. (CAT 1 cable)

Step 2: Open your coupler

Apply pressure to break it open at the center, in the same way you might break a twig. You may press it up against the side of your desk if it helps. You will see 4 wires, they should be color coded red, green, yellow and black. If they are not, it will be harder. The red and green cables are the one you should worry about. The other two are for the second line; it will not affect this project at all.
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wait, how do you call the other phone?

factory9094 months ago

What about putting a speaker on the other end instead of a phone? Would I need an amp for that portion?

schand51 year ago
I will try it first
nodoubtman1 year ago
what are you doing with green wire? then?
RTourn (author)  nodoubtman1 year ago
Nothing, don't cut the green wire.
bgtrammell1 year ago
I'm using two single slot pay phones, rewired as intercom, for childrens play. I have the power source connected directly to the handsets with a 330ohm resistor. I have audio but with a loud buzz. I've tried w &w/o resistor. all various wiring combinations and varied voltage from 9 - 15 - 24vdc but can't eliminate the buzz that over rides the voice. Is there a fix?
RTourn (author)  bgtrammell1 year ago
First try using a 9 Volt battery. If that fixes the problem then the issue was your power supply was noisy. The easiest fix would be to use a rechargeable 9volt. There is a way to fix this by adding some high capacitance capacitors to the circuitry, but I don't think I can adequately describe how to do that in a few paragraphs without knowing your setup.

Or you may be getting electromagnetic interference from the house power lines which run at 60Hz (US). You can verify this is the case by wiring you're phones along a different path away from power cords and make sure you don't bundle the phone wires with electrical wires.

I hope one of these solutions works for you.
ilpug2 years ago
I really want to make this now, seeing as how I have a ton of old phones. I might use a rechargeable battery though.
Is the flavor of the milk optional? Is there any flavor you suggest? Thanks!
No, you must use Orange flavored milk. If Orange flavored milk is not availible, any citrus or acidic fruit can be used as a substitute.
Is this wireless? I want to make one for my woods
s1966352 years ago
Does any one know how to use the dial pad if i wanted to use button number 1 to ring/connect me to that phone because i have it conected to my house phone line( Not easy)
Any ideas ??
xucaen2 years ago
I have no clue what you are doing. How do these phones talk to each other? What are you doing with that battery? Can you do this with two cell phones as these people suggest you can do?
jalke1162 years ago
Can you use more than 2 phones?????
agnestre2 years ago
Is 270 ohm 2W OK?
exactly what do the cords connect to? from what, to what?
Smart Plan3 years ago
Thank you for this! It Really Helped Me and my Friend !
lesklassen6 years ago
Can you do a 4 phone system?
RTourn (author)  lesklassen6 years ago
Although I haven't tried it I'm very sure all you need is a triple phone jack.
How would you configure an intercom with a 3-way phone splitter?
no. That requires a different circuit.

Go here and scroll down to "theatrical intercom"
civicturbo3 years ago
Nice instructable! I saw this idea in 1988 at a science fair at the local county fair. They used wall power, 12v DC, a regulator, cap to clean the DC from ripple fullwave bridge rectifyer, a sand resistor on each wire from the power supply and ran it in parrallel with the phones in parrallel. Then used the second pair in common phone station wire and created a ring by wiring a doorbell button at each end and a buzzer at each end. worked really well. I went to radio shack and bought most of the parts for the power supply and tryed it. Worked good. Ive also seen this done with a 12v latern battery, everything in parrallel w/no sounder.
vlasktom7 years ago
will hooking a regular power cord up to it, and plugging it into a wall outlet create a ring?
RTourn (author)  vlasktom7 years ago
It may ring, but probably blow a capacitor, or catch fire. There is more current than you need. Spark Fun has a great little article and schematic on how to build a ring generator. they use it in a slightly different way but it has all the right gut. At some point I'll adapt it for this project.

Here is the website:

joinaqd RTourn5 years ago
does it work without the ring generator?
If you read it it says the ring generator is for the ringer. This does not have any effect on using the phones for the intercom, just the ring feature.
Thebighat994 years ago
How about two of the same phones with a transfer function. Then when you want to talk to other party. just hit transfer the other phone would ring then hang up then talk to each other. Would that work for ring generator?
playpep4 years ago
Would a 330 ohm resistor work?
ReeceLV4 years ago
Could you maybe use the wires for the second line for a buzzer or some leds ? I mean that you do it so that if you flick a switch a buzzer or some lights at the other end notify the person
alleyezonme6 years ago
hey, your instuctables was AAAWWWSSSOOOMMMEEE!!! Did You know i was your biggest fan? anyways, can you pleeeeeeese make an instructable about how to make the ringer!? oh, and also I need to now how much energy it takes to get the the ringer to ring, and how to make it ring. so please help me out here. your best fan, Alleyezonme
Ringing is rather more difficult. You need to generate a ~45v AC wave length at 50 or 60Hz. But there are *plenty* of schematics and information online. Google is your friend.
It is actually 20 Hz.
vicvaneyck6 years ago
So the resistor isn't really needed? What can go wrong when you don't use it? And when you use cordless phones, do they still need to be plugged into electricity?
The resistor may not be required for wall-powered cordless phones, but are mandatory for other phones. Use the resistor!
luck vicvaneyck6 years ago
I can answer your qeustion about the cordless phone u would still need to plug them in for the wireless part to work
Yes they have to be plugged in
bombmaker25 years ago
does the watts on the resistor matter
yes. anything above a 1/4 watt should be fine. Too small and the resistor will fry.
RTourn (author)  bombmaker25 years ago
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