A musician from lower Saxony named eVADE/duality micro has produced a cable to sync up Game Boys running popular homebrew software with Korg drum machines and synths.
On the Game Boy side, you need either LSDJ or nanoloop cartridges for music tracking. The cable then connects to the Gamelink Port or your Nintendo handheld.
On the Korg side, the volca series and monotribe can take that input via their sync port. (The Game Boy has to be the clock master with LSDJ, at least, for now; nanoloop appears to work both directions. A future LSDJ may also send.) I believe this should also work with devices like Teenage Engineering’s Pocket Operator line or some iOS apps – anything capable of responding to the Korg-style sync pulse, which has become something of an unintentional de facto standard.
Stop breadboarding and soldering – start making immediately! Adafruit’s Circuit Playground is jam-packed with LEDs, sensors, buttons, alligator clip pads and more. Build projects with Circuit Playground in a few minutes with the drag-and-drop MakeCode programming site, learn computer science using the CS Discoveries class on code.org, jump into CircuitPython to learn Python and hardware together, or even use Arduino IDE. Circuit Playground Express is the newest and best Circuit Playground board, with support for MakeCode, CircuitPython, and Arduino. It has a powerful processor, 10 NeoPixels, mini speaker, InfraRed receive and transmit, two buttons, a switch, 14 alligator clip pads, and lots of sensors: capacitive touch, IR proximity, temperature, light, motion and sound. A whole wide world of electronics and coding is waiting for you, and it fits in the palm of your hand.