Interface a rotary phone dial to an Arduino

Step 2: Identify the switch

Once the dial is out, it should be relatively easy to see how the dial converts rotary movement into pulses. Try spinning the dial by hand and watching the movement on the back. You should see a switch making and breaking a circuit rapidly - so if you dial '9', the switch should engage nine times.

For those of you who may never have used a rotary dial before - remember that the dialing only happens when you let go the number and let it spool back .

I've documented how it works for my phone in the Notes of the photo below.

There's also a blurry video of the mechanism working.