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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chabong7 years ago
OMG it actually works. my band has tried different things to talk to each other like walkie talkie and stuffs but this is the best solution. We bought 2 sets of the GE DECT 6.0 follow the instructions above and all 4 handsets can communicate. Now i have to make it some how louder and less noisy. Can I use 12 volt instead? Thanks.
M.K1 chabong4 months ago

If you're using a set of 4 matching multi-handset DECT 6.0 cordless phones, look in the instructions (if you still have them) for how to set them all up to talk to the same base. If you can do that, you won't need the project this instructable is for...

lk-8 years ago
This hack does not qork in Portugal. I think our phones are different from yours. Our phone line power its 47votls. what can i do?
static lk-7 years ago
Here in the States the Central Office provides a nominal 48 VDC . Evedently the cordless base units are happy when presented with 9 VDC, I would expect yours should be too, one volt isn't that much. If you have one use a variable DC power supply use it to determine what voltage makes your units happy.
maker12 static6 years ago
use a 12 or 7 v lantern batt
maker12 maker126 years ago
also use a 1 ohm 1 of 2 watt SANDSTONE ristor in siries
standalone resistor in series? thats what the spell check is for.
well sandstone is right because its a resistor embedded in stone,with the leads poking out
M.K1 Derin4 months ago

I'm guessing they meant to say "Sandbar" resistor... They call it that because the resistor is encased in a bar of cemented sand...

bgtrammell2 years 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)  bgtrammell2 years 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.
M.K1 RTourn4 months ago

If I were to use an AC/DC power adapter, what would be the recommended current rating, and what value of capacitor would do the job if I have hum then?

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:

M.K1 RTourn4 months ago

If anybody else is looking for that article, it has been moved to:

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.

wait, how do you call the other phone?

factory9099 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.
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 ??
xucaen3 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?
jalke1163 years ago
Can you use more than 2 phones?????
agnestre3 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"
civicturbo4 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.
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
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