The rotary phone dial is the pinnacle of user interface for satisfying, slow number entry! Originally designed for dialing phone numbers, you can now re-purpose this beautiful piece of machinery as a USB number pad to use with your computer or mobile device.

With the KB2040 Kee Boar and a bit of CircuitPython code, you can read the mechanical dial pulses and convert them to USB HID number key messages. You can also modify the code to type letters, or go even further and make your phone send MIDI messages.

This project is non-destructive and fully reversible, should you decide to restore your phone to it's intended purpose.


Rotary Dial Phone

A model 500DM telephone or equivalent with rotary pulse dialing mechanism. Designed by Henry Dryfus, and manufactured by Western Electric, with millions of them made between 1950-1980s. You can find them in basements, attics, closets, garage sales, thrift/vintage shops, and online auctions.

Licensed models later made by ITT/Cortelco, Northern Electric/Northern Telecom, and Stromberg-Carlson will work just fine.

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RJ11 Cable

If you want to create an unholy "telephone-to-USB" cable, you'll need some four-conductor phone wire with a typical RJ11 connector on one end.

The connector should be a 6P4C type.

Note: 6P4C (six position, four conductor) RJ11 jacks are used to plug the phone base into the wall and are wider than the 4P4C (four position, four conductor) RJ9/10 jacks that are used to connect the handset to the phone base.

This guide was first published on Feb 08, 2022. It was last updated on Jul 19, 2024.

This page (Overview) was last updated on Mar 08, 2024.

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