Then I made the structure for the feedback LEDs, which will be placed under the touch sensors bar.

I needed a bar of polycarbonate like the one of the touch sensors:

Then I decided the colors for the various functions, and I started soldering the LEDs on the polycarbonate bar:

On the other side of the cables I soldered the 10-pin connector:

then I isolated the wires with heat-shrink sleeve:

A LED test:

I was not satisfied with the result, so I modified the bar of the LEDs: I removed the wire that joined all the LED cathodes, and I replaced it with two rigid wires, made from a single thick copper wire, instead of a braid of thin copper fibers.

Also I replaced some LEDs that were less bright than the others, and this is the result (compared to the previous pics, you can see how the lighting of the LEDs is more homogeneous, while previously the light of the low brightness-LEDs was too weak):