An intercom can be a useful tool or a fun toy. In this project, I am going to show you how to make a simple intercom using a pair of old corded telephones. This is an easy electronics project that is great for beginners and fun to do with children. 

Step 1: Materials

Two Corded Telephones
Phone Cord
9 Volt Battery
300 ohm Resistor (270 ohm or 330 ohm can also work)
Heat Shrink Tubing
9 Volt Battery Connector
Small Plastic Project Housing

Wire Strippers
A Sharp Knife
Soldering Iron
Screw Driver
<p>hi is it possible to connect 4-5 phones ?? How? </p><p>Is it possible to ring the phone 2 using a number or switch?</p><p>Is it possible not to use a resistor?</p>
Yes. Connect all the phones in series.<br />It is possible but adding a ringing function makes it a lot more complicated<br />If your power supply is 6 volts such as 4 AA batteries, then you would not need a resistor.
<p>Hi, do you think a public payphone type of phone would be suitable for this? Or does this only work only on the ordinary kind? </p>
<p>I don't know how public pay phones are wired up. But it is worth a try.</p>
<p>What type of 300 and 600 ohm resistor do I buy? How many watts, volts, etc? I looked online and there's many different types. A link to Amazon would be great.</p>
I used a 1/4 watt. The specific type doesn't matter.
<p>Hello. I successfully hooked up two old rotary phones together by using a 9v battery between them. Now, will using 9v with no resistors harm the phones in any way either in short time use or long term use? I can use 6v if that is better.<br><br>Another question: Inside the phone wire there are three wires; red, blue and white. I found out that white is (-) and red is (+). I am unsure what the blue one does. <br><br>Do you know if there is any signal output when phone 1 is lifted off? I wanted to hook it up so that a 12v buzzer sounds(next to phone 2) when the handle of phone 1 is lifted off. Maybe the third wire gives power when the phone is lifted off? </p>
<p>6 volts would be best. There can be as many as 4 wires in the cord. Just worry about the red one. The switch that is on the base of the phone just connects the signal wire when the phone is picked up so that you only hear someone when the phone is off the hook. But you could rewire it to use one of the extra wires to activate a buzzer.</p>
<p>Hello, I just attempted to do this project with two old 2554 phones. I have tried 3 different power supplies ranging from 5-8 volts DC with 200ma to 1 amp of current and none seem to be able to power the phones. Then I finally tried my 12 volt battery and it supplies enough power, but only 1 phone will transmit. I even replaced the handset cord to rule out a possible bad cord and eliminated the possibility of broken power wire. Any ideas as to why my circuit isn't working correctly? Thanks</p>
I don't know. One of the phones might be broken.
<p>I tested both out prior to attempting to do the project. Both phones worked on the phone line. I'll figure it out sometime. I only did the project because I thought it'd be something fun to mess with. </p>
<p>Hi, I am looking for any readily available cordless phones(pair) for intercom connectivity without phone line ...can you please suggest any model available online.</p>
Sorry. I have no suggestions.
<p>I built this to do an off grid intercom between buildings about 200 ft apart at my property. This part is really simple - the trick is to get it to ring. I successfully rigged a buzzer system, but now I'm trying to refine it to make the phones actually ring. I also modified the system to run of a micro solar system with a car battery rather than a 9 volt battery (Overkill, but I plan to add more stuff to the system). When I get it done, I'll post my own instructable.</p>
Cool idea.
<p>How difficult would this be to convert to a multi person system. say 5 users. Do you just pigtail all the wires together?</p>
<p>I am not sure. You could probably just connect them in series in a big loop. Try connecting the red wire to the green wire of the previous one until they are all connected.</p>
<p>Hi am Keshav see brother ur given just 2 telephone intercom connection yes that is really good but i want go hot line connection how its please give me suggestion </p><p>Thank you </p>
I am not sure I understand what you are asking about. Could you please clarify.
<p>Hello! Can I ask something? Can you put a schematic on how you put a buzzer / led to both telephones?</p>
You can just wire them up in series like this<br />http://cdn.instructables.com/F2D/MLM1/HEBNHKGW/F2DMLM1HEBNHKGW.LARGE.jpg
<p>I made the project and I also added a on/off switch. I also changed the project box to an altoids tin lined with duck tape on the interior</p>
<p>I need to run a line about 150ft long will this work?</p><p>Can I power it off a 12v battery?</p><p>What does the resistor do? Will I need it?</p><p>Thanks, Kaden</p>
Yes it will work. Yes you can use a 12 volt battery. All you to do is use a slightly larger resistor. The resistor drops the voltage down to about 6 volts (the voltage that the parts are designed to work with). If you are using a 12 volt battery try using a resistor that is close to 600 ohms.
<p>thanks for the clairifictaion!</p>
<p>You could set up a buzzer system by reusing the same 2 wires. Since the phones are out of the circuit when hung-up, you could reverse the polarity of the power supply &amp; use two diodes to &quot;steer&quot; the power to a set of buzzers.</p>
<p>This is what I mean. Expand image to see it all.</p>
<p>I dont quite get what you are saying. could you give a bit more detail</p>
<p>I want to set something up like this but with rotary phones. Preferably candlestick phones. Problem is I dont have the phones yet to figure it out. Something so you click the holder twice it rings phone 2. Three times for phone three ect. Someday Ill figure it out.</p>
And you can get all of the parts you need, at you local Radiosh......Damn
HA HA HA!<br>Good point. I should update that.
<p>Every plan I've seen for this requires the 300 ohm resistor. Why? What does it do? Wouldn't it just drop the voltage and nothing else?</p>
Yes. It drops the voltage to the appropriate level. The phone actually needs about 6 volts to run. The only reason that a 9V battery is used is because it is a little more convenient to work with. If you used a 6 volt battery pack you could probably leave off the resistor and be fine.
<p>Would it possible to do this with two fax machines? I am curious as most fax machines have a separate mains connection for the mechanical parts to operate, the printer and scanning components for instance. I am wondering if the analog phone components run in parallel to this circuit and they are isolated or they use the same source. </p>
Maybe. I don't really know how a fax machine's internal circuits work.
<p>Would it possible to do this with two fax machines? I am curious as most fax machines have a separate mains connection for the mechanical parts to operate, the printer and scanning components for instance. I am wondering if the analog phone components run in parallel to this circuit and they are isolated or they use the same source. </p>
<p>Is there a way to get the other phone to ring ? like an extension number or something ?</p><p>That would significantly increase its usefulness.</p>
Like veeguy said, much more practical to utilize whats already there, the other 2 unused lines in the phone cord. Theres a million and one ways to get it to ring (oscillate) the phones onboard transducer, if your not savy with discrete components, use a MCU like and arduino or something.
<p>To get a corded phone to ring, you need to send aprox. 90 volts AC through the same line as the 9 volts DC is sent through. It might be more practical to use the other 2 wires ( yellow &amp; black ) in a phone cord to ring a chime or buzzer on the other end. Put a momentary on pushbutton switch on each end to send a ring signal to the other end. Push the button to signal the other end to &quot;pick up&quot;.</p>
<p><a href="http://www.epanorama.net/circuits/telephone_ringer.html" rel="nofollow">http://www.epanorama.net/circuits/telephone_ringer.html</a></p><p>To make the phone ring you'll need to raise the line voltage to ~70VAC@20Hz</p>
Just curious.... Why would this be useful? :)
<p>A lot of houses have phone wires throughout the house, with phone boxes in most rooms. These boxes are all, theoretically, connected. One option would be to inject current into the line and then have readily accessible intercoms for each room.</p>
<p>I had this same thought, but you have to remember to disconnect the house from the outside telephone system or you run the risk of sending a charge back to the central office and damaging their equipment or injuring a line worker (very small chance, but why risk it?).</p>
A 5 cent diode will fix that issue :)
<p>I have a two floor house with a very dispersed layout (lots of halls), a garage and a barn where I have a workshop on one floor, practice area on another and intend to make the third floor into useful space at some time...</p><p>My house also has three doors that get used a lot and have no door bells; people either call our cell phones or think we are snubbing them when we don't hear the knock - we can't hear the kitchen door (next to the driveway) from the living room and we can't hear any of the doors when we are upstairs in the bedroom.</p><p>We have to yell to be heard between the floors and even then we tend to have to walk to the middle of the house where the stairs are and ask the other person to repeat themselves..</p><p>I've been wanting to install an intercom system since I bought the house. With a trip to Goodwill, this one would cost me only about $25.</p>
<p>Intercom house to shop, playhouse to kitchen, access gate to house, etc.</p>
Mostly I see this as something that children would use as a toy. But you could set it up just like a regular intercom and use it to communicate across a house or to a workshop or front gate. There are a lot of potential uses even if they all seem a little ridiculous.
<p>House to garage/barn/greenhouse etc.</p><p>If you can ring the other phones it would be infinitely more useful.</p>
I've measured the average voltage of a phone line to be about 50v.. Surely a 12v supply would be adequate?

About This Instructable




Bio: My name is Jason Poel Smith I am a Community Manager here at Instructables. In my free time, I am an Inventor, Maker, Hacker, Tinker ... More »
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