For main keys I wanted to use 24mm arcade buttons like these as they have micro switches ( which means a softer, easier press) and they're transluscent. Which means it can pass light so I can use RGB leds with each one to assign different color functions

As usual, we don't always get what we want, The only available arcade buttons in this country were these 35mm and 45mm buttons with a cost of 35 or 45 LE each, and I needed 9 of them which meant a cost of 315-405 only for the switches only, which almost exceeded my desired price for the product

I decided to use these limit switches, as it was the only affordable available microswitch . and to use a flexible printed key pad above it.

These Idea was inspired from a project by GreatScott a popular maker x Youtuber, he used the same mechanism but with normal capped push buttons, which I refused to do for two reasons: I didn't want to replicate+ Push buttons press is too hard for a musical instrument.

• Schematic design was simple as usual, I used female pin headers for the pico, but I had some missing footprints, which were ( slide potentiometer, limit switch and multiplexer) I'll attatch their libraries below.

To make the PCB buttons alligned with enclosure holes, I took a sketch of the enclosure face and exported it as a dxf and imported it to eagle using the following ULP: import-dxf.ulp

I designed a 150x150x30 mm box for the encloure with a white acrylic back.

It was easier for me to draw all features on the same sketch to be easier to edit. and to have accurate symmetrical and ergomical design.

The PCB didn't fit well for a reason that I didn't have time to search for, so I sized it down using a small saw and some sanding paper and the result was acceptable. and the switches were alligned well with the square holes. but it was going to be better if the switches were 180 degrees rotated to make the limit switch lever better alligned.

there were minor scratches on the top caused by the 3d printer bed, but it has nothing to do with functionality

The keypad fitted will in it's required place but it was stiff, if you pushed it lightly it doesn't move, If you pushed it hard, it's removed from the enclosure.

I used an open source code by a Brazilian music technology engineer and maker called Gustavo Silveira, it's a thousand line code but he designed it in a great way to be easily customized to any number of keys and pots with multiplexer or directly to the I/O pins.

The code uses the following libraries:

• Multiplexer4067.h to easily use our multiplexer

• Thread.h it creates virtual threading that makes the potentiometer response faster

• MIDIUSB.h it makes the device recognized as midi device and makes it send midi signal using bottons, pots, etc.

After including libraries, he defines the multiplexer selector and output pins.

Then he starts defining variables for total number of pins, uC pins and mux pins .

then he creates an array with the midi notes assigned to each button to bes assigned to butons selected previuosly

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Then in the part using the virtual thread:

threadPotentiometers.setInterval(15); thread read rate (every 15 milli second)

threadPotentiometers.onRun(potentiometers) called function

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for (int i = 0; i < N_BUTTONS_ARDUINO; i++) {

buttonCState[i] = digitalRead(BUTTON_ARDUINO_PIN[i]);

} In this for loop, the uC reads the number of buttons connnectef directly to the arduino defined above in n_buttons_Arduino and saves it in a variable called buttonCstate

Then the same way is used with pots and mux, and the rest of the code is made of conditions if other uC were used. And the direct funstions that send midi notes through usb communication