fm1-cartridge

From the project's README ("Using it on the FM-1"):

1. Power the cartridge from its battery and connect its USB to the FM-1, switched on.
2. Hold HOME, select the USB section and set USB RETURN to 100%; leave the menu. Keep the speaker volume low but audible.
3. Select track 1. Once the cartridge answers, the track on the cartridge's MIDI channel (channel 1 by default, under GLO → MIDI) is the cartridge track: its footer, TRACKS and the PRESETS page show the cartridge's engine and preset, and its internal engine stays silent.
4. Play. The keys, chords, arpeggiator, steps, rolls and recorded takes of the cartridge track play the cartridge over MIDI, with GLO → SYSTEM → OUT left at KEYS.
5. Turn PRESETS on HOME, TRACKS or the PRESETS page to step through the cartridge's presets; past the last preset of an engine it goes on into the next engine.

Tap GLO and turn SELECT to CARTRIDGE: knobs 1 and 2 choose engine and preset, 3 a parameter and 4 its value. The header shows the running firmware (CLIPPER OK, MELODEE OK, FELUCCA OK) or NO LINK. To switch synthesizer, stop the transport, turn knob 3 to FIRMWARE and knob 4 to a slot: the cartridge reboots into it 2 s later. Each firmware keeps its sound, MIDI channel and edits on the cartridge.

The user guide walks through every step, from connecting the cartridge to switching firmware, with a troubleshooting table.

Read the full instructions

From the project's README ("Safety and risks"):

> Read this before building or connecting anything. The cartridge is an experimental > prototype: hobby modules, a lithium cell and a USB connection outside the Type-C power policy, > attached to a commercial instrument whose firmware is replaced. A mistake can damage the FM-1, > the ESP32-S3 board, a computer's USB port or the cell, and a damaged lithium cell can vent or > catch fire. Everything here comes without any warranty (GPL-3.0, sections 15 and 16); build and > use it at your own risk.

• The cell. Use a protected 1S LiPo, check its polarity with a multimeter, insulate every joint, and never crush, puncture, heat or charge it unattended.
• Power sources. Never connect the cartridge to a computer or a charger while it is plugged into the FM-1, and connect nothing but the cell and its switch to the board's power pads.
• The USB link. Both boards present themselves as USB sinks; the link works outside the Type-C policy and depends on the cable, orientation and order. No hubs, chargers or other devices in between.
• The FM-1. Its firmware is replaced by a modified Sloop, which can hold the FM-1's charger off through a register bit whose effect is not measured. Back up the FM-1 first; the vendor's firmware can be put back.
• Low cell. On the prototype, a partly discharged cell takes the ESP32-S3 below its minimum supply voltage.
• Volume. A fault can produce full-scale noise: start with the FM-1's volume low.

Details: electrical risks and …

Read the full instructions