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A classic MIDI interface module for Adafruit’s STEMMA interface #STEMMA #Adafruit #MIDI @Adafruit @CedarGroveMakr

A classic MIDI interface module compatible with the UART mode of Adafruit's STEMMA

Cedar Grove Studios has produced a clever interface board translating between the Adafruit STEMMA I2C interface and a classic MIDI connection.

The STEMMA MIDI interface is a self-powered, one-quarter protoboard-sized module for use with Adafruit STEMMA-compatible products. The interface converts incoming and outgoing classic MIDI current-loop input and output to STEMMA 3.3-volt logic. This interface requires that the host STEMMA interface be placed into UART mode with a fixed rate of 31,250 baud.

The module has two ways to connect UART signals: a STEMMA-compatible 4-pin JST connection is provided on the top edge of the module, and two four-pin strips are available to allow header-style or soldered connections. The header-style connections allow the module to be used with UART signals from sources without a STEMMA interface connector. All power, ground, and RX/TX pins of these connectors are wired in parallel via printed circuit board traces.

The Type B (3.5mm TRS) MIDI input is an optically-isolated Type B 3.5mm TRS connection. The Type B (3.5mm TRS) MIDI output is buffered. On-board receive (RX) and transmit (TX) LEDs indicate incoming and outgoing MIDI signals. Interface module power is supplied by the STEMMA’s 3.3-volt power pin.

The STEMMA MIDI interface

The OSH Park STEMMA MIDI module project page is at

The STEMMA MIDI interface was tested with CircuitPython version 3.1.1 and version 4.0.0 Alpha_5. Example test code for the Trellis M4 is provided in the repository.

See the code and details on GitHub.

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