A ready-to-go tool to reverse-engineer all the laptop keyboards that you want to reuse, and then to be used as an I2C-connected controller.

Why?

• Reuse laptop keyboards with your microcontroller and SBC projects
• Build your own Raspberry Pi-powered laptop inside another laptop's case while reusing as much as possible
• Make a very sleek USB keyboard that you can easily carry around
• Debug issues with replacement laptop keyboards
• Use this board as an I2C keyboard controller after you're done reverse-engineering

How?

Connect the keyboard to this shield, connect the shield to a Raspberry Pi or some other I2C host, then launch the reverse-engineering script and press the keys one by one, as the script demands. After finishing, you will receive:

• Pinout for the keyboard, showing rows, columns and unused pins. You will need this information for designing the controller PCB or properly programming an off-the-shelf controller.
• Table of keys mapped to physical pins on the keyboard. You will need this info to program whatever it is that you'd like to use as a controller.

This tool can also help you reverse-engineer the LED positions and the power/other separate button pins, if your keyboard has those.

Features

• Fully open-source - both hardware and software
• 32 GPIOs for keyboard pins
• 0.5mm, 0.8mm and 1mm pitch keyboard connectors
• Kinda follows the RPi HAT format
• • Has no EEPROM, as it doesn't use any kernel drivers or overlays
• • The board outline is extended so that the 1mm pitch pin header would fit. That means the board will stick out of i.e. a Pi case, however.
• Has resistors protecting the GPIOs from short-circuiting
• Can be hotplugged safely onto a powered Pi
• Can be used as a keyboard controller with extra code

The board comes with a 40-pin GPIO header for Raspberry Pi connection. It's easier to ship these unsoldered, if you'd like me to solder it, you should pick the corresponding option!

Notes

I had to increase the product cost because MCP23017 expanders are currently very hard to obtain and where they're available, they're being price-gouged. You can still get MCP23017 relatively cheaply on eBay/Aliexpress as part of breakout boards, but it's clear to me that the stock will be limited there, and if I were to buy those for my product, I'd deprive other hobbyists from I2C GPIO expander breakouts.

This is an experimental run of these boards, to gauge interest, work through usecases and raise funds for the next batch. When I was sourcing parts for this batch, I only could get 30-pin 1mm connectors. Some keyboards out there use a 32-pin 1mm connector, however. If you want to RE such keyboards, I have some 32-pin connectors available to me that I can get from laptop motherboards, however, that option is not something I can offer to everybody, which is why it's at extra cost.

During rework, I ruined a few of the 0.5mm connectors on these boards. If you don't plan to reuse keyboards on very modern laptops, which sometimes use 0.5mm connectors, you can save a bit of money by not going for an 0.5mm connector!

The next batch will have 32-pin 1mm connectors by default, as well as a way to connect non-standard keyboards - i.e. Thinkpad keyboards, DIY keyboards, commercially made mechanical keyboards etc.

Connectivity

• Two MCP23017 expanders connected through I2C
• Requires 4 pins in total (GND, VCC, SDA and SCL), and an extra pin (INT)
• INT pin is not required for me software to function, but is available for your own experimentation - see below for an explanation on that
• Can be used with a Raspberry Pi (like a HAT), a BeagleBone, or other I2C-equipped Linux systems - even a laptop as long as you can get to I2C pins!
• Will work with VCC and IO voltages in 3V-5.5V range

FAQ

• Q: What if my keyboard has different pin pitch/connector/more than 32 pins?

• A: Message me and we will figure out a solution for that =)

• Q: I have this other question about reusing laptop parts, keyboards or otherwise...

• A: Ask me on Twitter or Hackaday.io - I'm always happy to help when it comes to reusing laptop parts!

• Q: How does it work?

• A: The software uses the GPIO expanders to scan the keyboard pin-by-pin, filtering weird pins (i.e. permanently shorted pins) and waiting for your keypresses.

• Q: What is the INT pin for?

• A: It could be useful if you wanted to reuse this board as a controller for your keyboard. While it's not the primary use and it will only work through I2C (not like a USB keyboard), it's very doable and only needs a bit of extra software. If you want to do this, the INT pin will save you a lot of CPU power - without the INT pin you would need to poll expanders over I2C constantly, which is neither efficient nor low-power-friendly.

The controller mode is something that I don't currently have finished code yet, but it's already being written, and by the time you get your expander, I will likely already have published the first versions of controller mode code.