Turns out the pogo pins on the X1 Tablet keyboards (gen 1,2 & 3) are just USB. 6 pins. 2 NC (not connected) and 4 standard USB [red (+5v), white (data+), green (data-), black (gnd)].
Thanks to cc9cii over on the /r/thinkpad subreddit we now have the pinout for the Gen1, Gen2, and Gen3 keyboards. The Gen1 and 2 are the same with 2 staggered rows of 3 pins and the Gen3 is 1 row of 6.
While the keyboard is facing you the pinouts are as follows:
Gen1 & Gen2:
- top row: white (data+), red (+5v), NC
- bottom row: black (gnd), green (data-), NC
ThinkPad X1 Tablet Gen 3 Thin Keyboard (01HX850 / Model TP00089K1):
- NC, red (+5v), green (data-), white (data+), NC, black (gnd)
Ideally a magnetic pogo pin connector could be used to connect to the keyboard in the same way the tablet does but I’ve yet to find one that’d work. Another solution would be to build a 3D printed clamp. I was impatient and ended up cutting off the end of an old USB cable and soldering to the pogo pins. At some point I plan to purchase a female USB C or Mini B port and replacing the cable.
Update: Ended up buying a usb micro breakout board from AliExpress and epoxied that onto the edge and wired that up instead.
- The Gen1 & Gen2 keyboards apparently requires drivers for the trackpad.
- Gen3 trackpoint and buttons don’t currently work on Linux
- Not all function keys will work on a typical system.