Interface a rotary phone dial to an Arduino

An old rotary phone can be used for a number of purposes in your Arduino projects - use it as a novel input device, or use the Arduino to interface a rotary phone to your computer.

This is a very basic guide describing how to interface the dial to an Arduino, and get the number dialed passed into a computer over the Arduino's serial link.

Step 1 Remove the dial from the phone

First step is to remove the dial unit from the phone. I'm using a GPO phone of some sort from the 1970s.

On this phone, the dial popped straight out - I just needed to give it a tug. If it doesn't, you may have to open up the phone and work out how to get it off.

There were five cables connected to the back of the dial unit. On my phone, these were regular spade connections, so I loosened the screws and pulled them out. If you want to re-assemble your phone, remember to record which color wire goes to which connection.

Comments

[philip42]

Why is it necessary to disassemble the dial? Couldn't you read the pulses directly from the phone line (red and green wires). All it is is a sequence of open-close pulses from the mechanical dial.

[TechDante]

had a problem with getting teh wrong output to the numbers (1 became 2 and so on) solved it by changeing the debounce to 20mille seconds and this did the trick

[alexhb]

same setup here... makes for much easier programming ;)

[Montrose]

I like the Skype idea. One could install the necessary computer inside of an ornate base with a flat screen monitor mounted behind the phone and what ever other antique details. It could be a very Steampunk video phone or perhaps use aluminum and go with a Machine Age phone. Oh for the time to explore all the options.

[jtmcdole]

Idea:
-use as a dieselpunk safe/door lock.
-Interface dialer, handset, and google voice to receive and make calls from a physical phone.

[TechDante]

hello i am interested in electronics for my end of year project, but i am just starting out properly into electronics and programing and saw the arduino as a good starting point. could you recomend any reading material i could look into (already have the Arduino Notebook from their website and the make Magazine getting started with Arduino)

[Irregular Shed]

 On the dial I've pulled out to use there's another switch that opens when the dial is turned to a number and closes when it has finished pulsing. I'm planning on using that instead of waiting longer because I'm also going to be having a keypad matrix to scan and an LCD to power!

[kissiltur]

splendid, splendid. Haven't thought about pulse dialling since I stopped working for a telecomms equipment company, lo, these many moos ago.

I had fun explaining to my four year old about how this phone works a bit differently from all the phones he sees in the house.

[Father Christmas]

lol @ "many moos ago."

I too measure my time scale by bovine vocalization! haha

[Aerospaced]

Hang on a bit, you said that if you dial 9 that it will tap out nine times on the switch. As I recall, when hand keying a phone, you add 1 to every number.

[guidomax]

Hi,

Thanks for the comment - an interesting topic. It appears that the pulse dialing regime varies by geographic area, however in the UK (where this telephone is from) and North America, the number of pulses corresponds directly to the number dialed. This is certainly what happens for my telephone - obviously people in other countries may have to alter the source code to account for their particular phone.

Cheers :)

From en.wikipedia.org/wiki/Pulse_dialing :
In most countries one click is used for the digit 1, two clicks for 2, and so on, with ten clicks for the digit 0; this makes the code unary, excepting the digit 0. Two exceptions to this are New Zealand, with ten clicks for 0, nine clicks for 1, and so on, and Sweden, with one click for 0, two clicks for 1, and so on.

[PS118]

One word: Skype! ;)

[guidomax]

It's a plan - that'd be pretty cool!