I found the code and schematic by Joe Grand to interface a Parallax Propeller with the Gameboy Printer. I had an extra WiiChuck adapter that I thought would work with the Gameboy Link Cable, but I had to sand down both edges of the adapter so that it would fit. I also had to cut a trace and solder it to another pin.
Make a robot friend with Adafruit’s CRICKIT – A Creative Robotics & Interactive Construction Kit. It’s an add-on to our popular Circuit Playground Express, FEATHER and other platforms to make and program robots with CircuitPython, MakeCode, and Arduino. Start controlling motors, servos, solenoids. You also get signal pins, capacitive touch sensors, a NeoPixel driver and amplified speaker output. It complements & extends your boards so you can still use all the goodies on the microcontroller, now you have a robotics playground as well.