Reference Projects

For Players

We are not the first to add MIDI to a vintage organ. These projects by other builders proved out the approach — the same basic technique of reading key contacts through small chips works on organs from Wurlitzer, Hammond, Conn, and others. Our project builds on their work with a more capable computer board that adds wireless Bluetooth MIDI and USB alongside the traditional MIDI cable.

Community Projects

Adding MIDI to Old Home Organs (Instructables)

ATMEGA328p + 74HC165 approach. Uses the same shift register scanning technique planned for this project, but with an older microcontroller that lacks USB-MIDI and BLE-MIDI capabilities.

instructables.com/Adding-MIDI-to-Old-Home-Organs/

MIDI for Digital Organs (Hackster.io)

Arduino Mega implementation with code for both bussed and matrixed keyboard types. Particularly relevant because the 555 uses bussed keyboards.

hackster.io/Larason2/midi-for-digital-organs-f3756c

oxesoft/keyboardscanner (GitHub)

Keyboard-to-MIDI scanner with velocity support. Demonstrates techniques for measuring key travel time to generate velocity values — potentially applicable to the Orbit III’s dual-contact second touch system.

github.com/oxesoft/keyboardscanner

MIDI-Out Key Takeaways

1. 74HC165 shift registers are the standard approach — proven, cheap, fast, and the daisy-chain topology scales to any number of keys
2. Bussed keyboards need pull-up resistors — the shared ground bus means inputs float HIGH when no key is pressed; the shift register reads LOW on key press
3. Scan speed matters — a full chain of 19 shift registers at SPI clock speeds completes in microseconds, well within MIDI’s timing requirements
4. ESP32 is a generational upgrade over Arduino for this application — native USB-MIDI, BLE-MIDI, and enough GPIO/SPI bandwidth to handle 153 inputs without breaking a sweat

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MIDI-In / Organ Control

The reverse direction — receiving MIDI to control organ circuits — has its own body of prior art spanning virtual organs, Leslie controllers, and MIDI-to-CV converters.

Hauptwerk / GrandOrgue (Virtual Pipe Organs)

Software-based virtual pipe organs that define comprehensive MIDI mapping standards for organ control. Hauptwerk’s MIDI implementation covers stop (voice) selection, expression, swell, crescendo, and tremulant control — all via standard MIDI CC and Program Change messages. Their channel and CC conventions inform our Output Inventory MIDI mapping.

hauptwerk.com · GrandOrgue (open source)

MIDI Leslie Controllers

Several commercial products control real Leslie speakers from MIDI, establishing the CC#80 convention used in our Leslie Control design:

• Hammond-Suzuki Leslie 2101mk2 — purpose-built MIDI-controlled Leslie with CC#80 speed selection. The industry reference for MIDI Leslie control.
• Neo Instruments Ventilator — Leslie simulator pedal with MIDI input. CC#80 for slow/fast preset switching plus CC#1 for continuous speed in advanced mode.
• Voce V5+ Organ Module — MIDI-to-Leslie relay interface. Confirms that relay-based speed switching (Scenario A) is the standard approach for real motors.
• Motion Sound Pro-3T — rotary speaker with DC motor and continuous MIDI speed control, demonstrating Scenario B viability.

MIDI-to-CV Converters

The Orbit III CV interface draws directly from decades of MIDI-to-CV converter design. These products bridge MIDI’s digital messages to analog synthesizer control voltages — exactly what the Orbit III CV Interface does:

• Kenton Pro Solo mk3 — single-channel MIDI-to-CV with pitch CV, gate, velocity, and two auxiliary CV outputs. Demonstrates the DAC + op-amp gain stage architecture used in our Output Stage.
• Expert Sleepers FH-2 — 8-channel MIDI/CV interface in Eurorack format. Its multi-channel DAC approach (one channel per CV target) matches our MCP4728-based design.
• Doepfer MCV4 — 4-channel MIDI-to-CV with programmable CC-to-CV routing. Demonstrates the CC mapping flexibility needed for the Orbit III’s multiple control points.
• Polyend Poly 2 — modern MIDI-to-CV with 8 outputs and USB-MIDI input. Relevant for its USB-MIDI-to-CV path, which mirrors the ESP32’s USB-MIDI reception.

MIDI-In Key Takeaways

1. CC#80 is the de facto Leslie speed standard — every major MIDI Leslie product uses it, so our implementation follows suit for maximum controller compatibility
2. MIDI-to-CV is a solved problem — the DAC + op-amp gain stage architecture has been refined over 40 years. Our design uses the same proven approach with modern ICs
3. Coexistence matters — Hauptwerk and hardware MIDI-to-CV converters all implement panic functions and safe defaults, confirming that our MIDI panic design (CC#123) is standard practice
4. Virtual organ standards are directly applicable — Hauptwerk’s CC assignments for expression, swell, tremulant, and stop control map cleanly onto the 555’s physical circuits