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.

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)
wire-nippers
milk (helps keep you hydrated and keeps bones strong)
Dremel
Soldering iron
solder
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.

Step 3: Cut, strip and solder

Cut the red wire in the middle. You now have two red wires. Strip the ends of both red wires. Now you will need some basic soldering skills for the rest of this project.

This sight has some good tips if your new:
http://www.makezine.com/blog/archive/2006/04/how_to_solder_resources.html?CMP=OTC-0D6B48984890

Now solder one side of the resistor to one end of the red wire. Solder the other end of the resistor to one end of the 9 volt connector( it doesn t matter witch end). And the last side of the 9 volt connector will connect to the other red wire. It should look something like this. Now when you do this cut off exess wires from your resistor and 9 volt connector before you solder, remember it all has to fit back into the coupler when your done.

Note: int the photo I cut the yellow and black wires because they got in the way.

Note I also used 265 ohm resistor, because it was more handy. I have completed this project much earlier with out any resistor. Be careful if you do this, I am not sure what the implications are.

Step 4: Testing

Quick test, leave it open Plug two phones into both ends of the coupler put in the 9 volt battery and talk. You may use two old wall phones with no problems. If you use cordless you need to make sure you have power going to them before they will work.

If they work Seal the expose wire with black tape. Dremel out a little slit into one of the sides. This will be where the 9 volt connector wires will exit the coupler. Close up the coupler, and be careful not to break any of the soldering you did earlier. Bring the leads of the 9 volt connector out of that slit. See photo.

Step 5: Clean up

If you use two cordless phones you have just made a makeshift home base walkie talkie. Clean up your area and drink your milk call a friend.

Note: to ring one of the phones you will need a ring generator, but that is another project for another time. Have fun.

Step 6: Troubleshooting

Make sure the cable works:
Find a phone where you can hear the dial tone. Now hang up and replace the line with the cable you plan to use, check to hear a dial tone now. If not then your cable is bad.

Make sure the phones work:
Temporary replace your home phone with one of the project phones, check to hear a dial tone. Then make a call to see if the microphone and the speaker work in the handset. And to see if the handset has a charge if it applicable. If you fail to make a call for any reason the phone is bad.

Make sure the Coupler makes a circuit:
Take the battery out of the coupler. The battery must be out. Then go to a working phone and make the connections in this order

Wall jack------> to cable -------->to the Coupler-------->to another cable------->to phone

This will check if you connected the right wires in the coupler. Pick up the phone and listen you should hear nothing, if you do here a dial tone then the wrong wires are soldered, or you have short in the coupler. If you move the coupler and you hear scratching sounds then you have a bad connection, and must re solder or better insolate.

If you hear nothing that is a good sign so far, now take a screwdriver or something metal and complete the circuit at the 9v battery connector. You should hear a dial tone now. If not then your connection on the red or green is just broken somewhere and you have to find it.

The green wire is just a straight shot; you do nothing with the green. The red wire is in series with the 300 ohm resistor and a 9v battery. Make sure its set up like this. I hpe this was helpful, drink your milk and have fun.

Comments

[schand5]

I will try it first

[nodoubtman]

what are you doing with green wire? then?

[RTourn]

Nothing, don't cut the green wire.

[bgtrammell]

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]

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.

[ilpug]

I really want to make this now, seeing as how I have a ton of old phones. I might use a rechargeable battery though.

[dvandevender]

Is the flavor of the milk optional? Is there any flavor you suggest? Thanks!

[lug big lug]

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.

[project_builder]

Is this wireless? I want to make one for my woods

[s196635]

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 ??

[xucaen]

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? http://blog.dialaphone.co.uk/2007/12/13/14-things-to-do-with-an-old-cell-phone/

[jalke116]

Can you use more than 2 phones?????

[agnestre]

Is 270 ohm 2W OK?

[leggomylegoeggo]

exactly what do the cords connect to? from what, to what?

[Smart Plan]

Thank you for this! It Really Helped Me and my Friend !

[civicturbo]

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.

[vlasktom]

will hooking a regular power cord up to it, and plugging it into a wall outlet create a ring?

[RTourn]

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: http://www.sparkfun.com/commerce/present.php?p=High%20Voltage%20Ringer

[joinaqd]

does it work without the ring generator?

[tinkertoymania]

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.

[Thebighat99]

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?

[playpep]

Would a 330 ohm resistor work?

[ReeceLV]

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

[alleyezonme]

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

[xsmurf]

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.

[tristantech]

It is actually 20 Hz.

[lesklassen]

Can you do a 4 phone system?

[tristantech]

no. That requires a different circuit.

http://www.epanorama.net/documents/telecom/telephone_intercom.html

Go here and scroll down to "theatrical intercom"

[RTourn]

Although I haven't tried it I'm very sure all you need is a triple phone jack.

http://www.radioshack.com/sm-recoton-modular-triplex-phone-jack--pi-2459860.html

[MunkyCh333z]

How would you configure an intercom with a 3-way phone splitter?

[vicvaneyck]

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?

[tristantech]

The resistor may not be required for wall-powered cordless phones, but are mandatory for other phones. Use the resistor!

[luck]

I can answer your qeustion about the cordless phone u would still need to plug them in for the wireless part to work

[Gamernotnerd]

Yes they have to be plugged in

[bombmaker2]

does the watts on the resistor matter

[tristantech]

yes. anything above a 1/4 watt should be fine. Too small and the resistor will fry.

[RTourn]

no

[bombmaker2]

thanks

[Brandosmarto]

Hi, I have a question. What is the purpose of the resistor, can you make this project ring, and can it be plugged in using a transformer instead of a battery? Any of these questions answered would be helpful.

[tristantech]

You can certainly use a DC wall adapter. Just follow the instructable but solder the wires to the power supply instead of the battery clip.

The purpose of the resistor is to limit the amount of current (20-30 mA) through the talking circuit. Too  much current will be too much for the coils inside the speakers and microphones.

No, this project cannot ring. If you want it to ring, you need a very high voltage (50-90 Volts AC) at about 20 Hz. That's enough to give you a dangerous zap and 20 Hz is very unusual.