Originally I was thinking about laser cutting an acrylic case for the keyboard, but later decided to just use some cardboard and super glue (and some tape…) to make a rough looking case. I’m a complete noob at soldering. The soldering process took me about 8 hours, and designing & making the case took me one and a half. The dimension of the case is roughly 17.4 cm * 6.2 cm * 2.3 cm (front hight) ~ 3.6 cm (back). Under the protoboard is an Arduino and a 9V battery. I think the next step for this project is to figure out a way to replace the Arduino with just a single ATmega328 chip, making the keyboard even cheaper and thinner.
Inside the case: