The secondary expansion board that completes the 16-channel multiplexer pair. Provides 8 additional key inputs with NeoPixel feedback, connecting to Extension Board 1 through a female header.
Overview
Extension Board 2 is the companion to Extension Board 1. Together, the two boards provide a full 16-channel input array using a single 74HC4067 multiplexer (hosted on Board 1). Board 2 carries the remaining 8 key inputs (channels 8–15) and their corresponding NeoPixel LEDs.
The board connects to Extension Board 1 through a female pin header, creating a compact, stackable assembly that can be mounted side-by-side or back-to-back inside the console enclosure.
Key Features
- 8 key inputs — Channels 8–15 of the shared 74HC4067 multiplexer on Extension Board 1
- WS2812 NeoPixel LEDs — Per-key RGB indicators continuing the daisy chain from Board 1
- Female header connection — Plugs directly into the bridge connector on Extension Board 1 for a clean, solderless assembly
- Auxiliary debug pins — Channel states exposed for testing and troubleshooting
- Compact footprint — Designed to match Extension Board 1 dimensions for uniform mounting
Connection
Extension Board 2 receives its address lines, power, and data signals entirely through the bridge connector from Board 1. No direct connection to the MIDI Controller Board is needed—Board 1 handles all upstream communication.
Extension Board 1 (Bridge Connector)
│
│ Female header
▼
┌───────────────────────┐
│ Extension Board 2 │
│ │
│ [Key 8] [LED 8] │
│ [Key 9] [LED 9] │
│ [Key 10] [LED 10] │
│ ... │
│ [Key 15] [LED 15] │
│ │
│ [AUX Debug Pins] │
└───────────────────────┘
Usage Scenarios
The Extension Board 1 + 2 pair is typically used for:
- Stop tab arrays — 16 rocker-style stops controlling organ rank selections
- Coupler controls — Manual-to-manual and manual-to-pedal couplers
- Combination pistons — 16 preset memory buttons for quick registration changes
Multiple Board 1+2 pairs can be connected to different ports on the MIDI Controller Board, allowing consoles with 32, 48, or more stop controls.
Manufacturing
Standard 2-layer PCB with through-hole and common SMD components. Designed to be ordered alongside Extension Board 1 for cost-efficient panel fabrication.