My implementation focuses on USB Midi communication (Midi-in through the onboard USB-C port) and features a push button to cycle between wave types (sine, saw, square, pulse, triangle, and noise). An RGB led inside the button changes color according to the current wave type.
Other than the onboard speaker driven by an LM386 amplifier, Portami has a 3.5" mini-jack port to plug a pair of headphones. The audio socket has a switching mechanism, disconnecting the speaker when in use.
The whole setup is powered by a 3.7V, 1100mAh li-ion battery, recharged and protected by a TP4056 USB-C charger module. A regulator boosts voltage to 5V, providing power to the Midi keyboard.
Seeed Studio XIAO SAMD21 (Seeeduino XIAO)
TP4056 battery charger module
18650 or equivalent lithium battery
Voltage regulator (like boost converter MT3608)