Output Inventory

For Players

The Input Inventory catalogs everything the MIDI encoder reads from the organ. This page is the reverse — everything the MIDI encoder can write back. Imagine a DAW, foot controller, or another keyboard sending MIDI messages that control the Leslie speed, bend the Orbit III’s pitch, or select voices automatically. The organ already responds to voltages and switch closures internally; MIDI-In just generates those same signals from an external source.

Summary

Category	Targets	Control Mechanism
Continuous (DAC)	8+	Voltage via DAC + op-amp gain stage
Binary (GPIO/relay)	20+	Relay closure or solid-state switch
Total	28+

Target counts are approximate — bench investigation will confirm which circuits are accessible and safe to drive externally.

Continuous Targets (DAC)

These circuits accept a voltage that varies over a range. The ESP32’s DAC output (0–3.3V) is scaled to the organ’s operating voltage through an op-amp gain stage. See Output Stage Hardware for the analog interface design.

Target	Circuit	Control Mechanism	Voltage Range	MIDI Mapping	Confidence
Expression volume	Main amplifier gain	Potentiometer (VR)	0–12V (TBD)	CC#11 Expression	High
Expression slide	Orbit III Slide circuit	Potentiometer (VR)	TBD	Pitch Bend	Medium
Orbit III VCO pitch	Resistor ladder summing node	CV summing	0–10V (TBD)	Pitch Bend or CC	Medium
Wah-Wah cutoff	Switching & Special Effects board	CV or VR	TBD	CC#74 Brightness	Medium
LFO rate	Modulator on S&SE board	VR	TBD	CC#76	Low
LFO depth	Modulator on S&SE board	VR	TBD	CC#77	Low
Delta Pitch (detune)	S&SE board	VR or CV	TBD	CC#94	Low
Reverb level	Reverb drive circuit	VR	TBD	CC#91 Reverb	Medium

Note

“Confidence” reflects how certain we are that the circuit can be externally driven without modification. High = confirmed potentiometer that can be paralleled or replaced with a DAC. Medium = schematic suggests a voltage control point exists but needs bench verification. Low = circuit exists but control mechanism is unknown — may require signal tracing.

Binary Targets (GPIO / Relay)

These circuits are switched on or off — tab stops, speed selectors, and pattern triggers. The ESP32 drives relay modules or solid-state switches (via ULN2803 Darlington arrays) to simulate the mechanical switch closures.

Target	Circuit	Control Mechanism	MIDI Mapping	Confidence
Leslie fast	Motor speed relay/switch	Switch closure	CC#80 ≥ 96	Medium
Leslie slow	Motor speed relay/switch	Switch closure	CC#80 43–95	Medium
Leslie off	Motor speed relay/switch	Switch closure	CC#80 ≤ 42	Medium
Tremolo on/off	Tremolo circuit	Switch	CC#92	Medium
Vibrato on/off	Vibrato circuit	Switch	CC#77 or CC#1	Medium
Orbit III — Reed	Tab stop contact	SPST closure	Program Change 1	Low
Orbit III — Brass	Tab stop contact	SPST closure	Program Change 2	Low
Orbit III — String	Tab stop contact	SPST closure	Program Change 3	Low
Orbit III — Banjo	Tab stop contact	SPST closure	Program Change 4	Low
Orbit III — Harpsichord	Tab stop contact	SPST closure	Program Change 5	Low
Orbit III — Electro Piano	Tab stop contact	SPST closure	Program Change 6	Low
Orbit III — Vibes	Tab stop contact	SPST closure	Program Change 7	Low
Orbit III — Xylophone	Tab stop contact	SPST closure	Program Change 8	Low
Orbit III — Glock	Tab stop contact	SPST closure	Program Change 9	Low
Orbit III — Chimes	Tab stop contact	SPST closure	Program Change 10	Low
Rhythm pattern select	Rhythm section switch matrix	Multi-position switch	CC or Program Change	Low

Caution

Tab stop contacts in the 555 are mechanical switches with pull-rod linkages. Electrically paralleling them with relays is straightforward if the contacts are simple SPST closures to ground. Some organs use resistive ladders or multiplexed scanning for tab sensing — the actual contact wiring must be traced before committing to a relay approach.

Investigation Queue

These unknowns must be resolved at the bench before finalizing the MIDI-In hardware design. Each item feeds directly into the Output Stage Hardware specifications.

• Trace Leslie wiring — follow the console Leslie switch to the motor. Determine: relay-switched speeds? Variable voltage? What motor type (AC induction, DC, shaded-pole)? See Leslie Control for the full investigation plan.
• Acquire Orbit III service manual — the factory service manual ($30–50 on eBay) contains voltage specifications for every CV node. Without it, bench probing is guesswork. Required for all “Low” confidence CV targets.
• Probe tab stop contacts — measure the electrical characteristics of each Orbit III tab stop. Are they simple SPST to ground? Resistive ladder? Multiplexed?
• Measure expression pedal circuit — confirm potentiometer values, taper (linear vs. log), and voltage range at the amplifier control input.
• Measure CV node voltages — with the Orbit III powered and playing, probe the VCO pitch summing node, Wah-Wah control input, LFO rate/depth pots, and Delta Pitch control to establish actual voltage ranges.
• Test rhythm clock — determine if the rhythm section accepts an external clock pulse (for MIDI sync) or if it’s a self-contained oscillator.
• Measure reverb drive — identify the reverb driver circuit (spring tank drive amplifier) and determine if level can be externally controlled via voltage.
• Tremolo/vibrato control — trace the tremolo and vibrato enable circuits to confirm they are simple switch closures suitable for relay control.