The bass will have 4 individual picks to pluck each string. Each pick is attached to a shaft with a 3D printed part and will rotate with the shaft. The shaft is powered by a bistable rotary solenoid. When unpowered, the solenoid stays in one of two positions. When a voltage is applied, it will rotate to the other stable position. This motion will swipe the pick across the string, causing it to play a note.

The bass will be able to play 20 notes, which is adequate range for most songs. 4 of those are open strings, and the other 16 are fretted notes. Each fret that is used will have a linear solenoid actuator placed above it. When a voltage is applied, the solenoid will extend linearly, pressing the string down. This is how the bass will change the pitch of each string.

The volume of the bass will be controlled by a servo attached to it's volume knob.

The strings will be muted by a single bar with foam on the end. The foam will press on the strings to stop the current notes being played. A single linear solenoid will press on the bar to lower it.

Solenoids will be controlled, as with the other instruments, by a single Teensey 4.1 microcontroller. These 3 controllers will then be connected to a central Raspberry Pi, which will accept MIDI files and break them down into the instruments' respective parts. 

All components will be soldered to a custom PCB. Each linear solenoid is powered with a Darlington solid state relay. Each bistable rotary solenoid is powered with a h-bridge driver. The servo will be connected to 5v and ground on the PCB, with the PWM wire connected to the microcontroller.