Input Inventory
Summary
Section titled “Summary”| Category | Count |
|---|---|
| Digital inputs | 151 |
| Analog inputs | 2 |
| Total | 153 |
Digital Inputs (151)
Section titled “Digital Inputs (151)”| Input | Type | Count | MIDI Mapping |
|---|---|---|---|
| Upper Manual (Swell) | SPST silver contacts | 44 | MIDI Ch 1, Note On/Off |
| Lower Manual (Great) | SPST silver contacts | 44 | MIDI Ch 2, Note On/Off |
| Pedalboard | SPST contacts | 13 | MIDI Ch 3, Note On/Off |
| Orbit III Contact 1 (note) | SPST mini-key | 25 | MIDI Ch 4, Note On/Off |
| Orbit III Contact 2 (aftertouch) | SPST mini-key | 25 | MIDI Ch 4, Channel Pressure or CC |
| Digital total | 151 |
Analog Inputs (2)
Section titled “Analog Inputs (2)”| Input | Type | Count | MIDI Mapping |
|---|---|---|---|
| Expression pedal (volume) | Potentiometer | 1 | CC#11 (Expression) |
| Expression pedal (slide/bend) | Potentiometer or switch | 1 | Pitch Bend |
| Analog total | 2 |
Shift Register Allocation
Section titled “Shift Register Allocation”151 digital inputs require 19 daisy-chained 74HC165 shift registers (8 inputs each = 152 channels, one spare).
Suggested allocation:
| Registers | Input Group | Inputs | Channels Used |
|---|---|---|---|
| 1–6 | Upper Manual (Swell) | 44 | 48 (4 spare) |
| 7–12 | Lower Manual (Great) | 44 | 48 (4 spare) |
| 13–14 | Pedalboard | 13 | 16 (3 spare) |
| 15–17 | Orbit III Contact 1 (note) | 25 | 24 (need 1 from next) |
| 18–19 | Orbit III Contact 2 (aftertouch) | 25 | 16 + overlap |
The exact allocation will be finalized during hardware design once the physical wiring layout is assessed.
Key Contact Characteristics
Section titled “Key Contact Characteristics”- Contact type: Silver-plated SPST
- Signal at contact: 0-12V square wave at note frequency (when key pressed)
- Bus architecture: Bussed keyboards — shared ground bus, key press pulls input LOW
- Scan approach: Read the INPUT side bus wires going to divider-keyer ICs