via this eBay listing
"Synth:Bit – 16‑Note Micro:Bit Synthesizer Keyboard Module with OLED Display, Battery Pack & Audio Jack, Lego‑Compatible Base, Matrix Inputs, Jumper Pins for Expansion
16‑Note Synthesizer for Micro:bit — turns your Micro:bit into a full octave keyboard (16 inputs in a 4×4 matrix) for creative music projects and experimentation.
Integrated Audio Output & Battery Pack — built‑in audio jack to hook up a speaker and a portable battery pack so you can use it anywhere.
OLED Display & Intuitive UI — clear screen interface for visual feedback, settings, and control of synthesizer parameters.
Lego‑Compatible & Breadboard Friendly — board spacing fits LEGO bricks; jumper pins allow easy breadboard or external keypad integration.
Expandable & Open Source — supports expansion via jumper pins, external keypads, or custom builds; program via MakeCode, Python, or microcontroller tools."
