Touch keypad for fischertechnik

Uses a cheap ripoff of the retired SparkFun Capacitive Touch Keypad from aliexpress. There's different versions, I assume they all use the same overall layout, though.

Warning: My board came with faulty soldering of the MPR121 chip. It showed up under the address 0x7B but wouldn't work otherwise. It seems some pins were either short-circuited to other pins or not connected at all. With a lof of flux and resoldering I got it to work as expected with the 0x7A address. If some of the keys don't work, most probably it's due to too much, not too little, solder.

For printing the transparent part: The standard diagonal criss-crossing pattern results in lots of tiny air bubbles which will cloud the view. So the most important trick, not mentioned in most transparent printing guides, is making Cura print only parallel lines by putting "[90,270]" into theTop/Bottom Line Directions option.

Use the provided LibreOffice Writer document to print a key layout of your choice.