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Source files and schematics for a very small, 33-key mechanical keyboard
Eagle C C++ Other
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hardware Moved schematics Mar 18, 2014
pictures Added pictures Aug 20, 2013


This project is the teensy code for Will Yager's custom mechanical keyboard project. (blog post)

The code serves two functions:

  1. If plugged into USB, the device will act as a stand-alone keyboard with 33 keys. ("The master")
  2. If a second device is plugged into that first device, the two devices will share relevant information over I2C. In this way, two of these devices can be connected to form a 66-key keyboard. With some modification to the firmware and the I2C pull-up resistors, one could theoretically chain up to 129 boards together (I believe).


  1. Install avr-gcc.
  2. Install Teensy loader.
  3. cd src
  4. make
  5. Drag main.hex into Teensy loader.
  6. Program Teensy.

Modifying key layout

  1. Modify keys[] in KeyMapper.cpp.
  2. Replace values like KEY_A with other values from keylayouts.h.

This should be fairly simple to figure out. Within the file, I have keys[] laid out just like the physical keys.

Program structure


       Start USB/I2C
       Determine master/slave status
              => get hardware state from HardwareController
              => debounce buttons with ButtonDebouncer
              => detect changes in buttons with ButtonDeltaDetector
              => map button changes to key changes with KeyMapper
              =: key_changes

              => update the slave (if it exists) with the SlaveNotifier
              =: slave_key_changes

              key_changes, slave_key_changes
              => notify the master (over USB or I2C) of key changes with the MasterNotifier
              =: led_status

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