REMI Synth 'Lite' - MIDI sound module (DIY) notes

REMI Synth 'Lite' variant
Monophonic MIDI Sound Synthesizer based on PIC32MX MCU

A DIY Project by M.J. Bauer

remi synth lite

The REMI Synth 'LITE' is battery-powered with OLED display and headphone amp.

Designed especially as a companion sound module for the REMI 2 handset (MIDI wind controller), this 'Lite' version of the REMI Synth is a more compact battery-powered device using the same "sound engine" software as the other REMI synth models (also based on a PIC32MX MCU). The 'Lite' synth can be attached to the player's belt or pocket with Velcro or a metal clip, allowing more freedom of movement while playing through headphones. A wireless audio transmitter (as used on electric guitars) may be plugged in for cable-free performance with an instrument amplifier.

The front-panel user-interface (GUI) is simplified, providing only a few essential day-to-day operations. The GUI comprises a tiny (1.3 inch) OLED display and 2 push-buttons.

The back panel provides a MIDI IN socket (DIN-5) with "power-over-MIDI" (5V DC output) to support a REMI 2 handset or any other MIDI controller with a classic MIDI OUT connection. There is a headphone socket (3.5mm TRS jack) and a low-level output (1/4-inch phone jack) for connection to an instrument amplifier.

A USB port provides the same command-line user interface (CLI) as the other REMI Synth models. The USB connection can supply 5V DC power to the synth module. It also powers the built-in battery charger.
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front view

back panel

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The circuit board is built around a PIC32MX340 "audio dongle" designed by a project follower "Chua" who lives in Singapore. Chua's PCB has provision for the I2C EEPROM (24LC08) and PWM audio output components, but access to MCU I/O pins is very limited, so the PCB must be "hacked" to get enough I/O for the synth.

For example, a pair of test-point pads (RC13, RC14) are used for the two push-button inputs. The I2C bus signals (SCL, SDA) required for the OLED display are accessed from the EEPROM (pins 5 & 6). The 6-pin ICSP header provides a further two port pins (RB6, RB7) which are used in the battery charging circuit.

Chua dongle PCB