Microcontroller Pin Selector

Use it online: https://ccrome.github.io/microcontroller-pin-selector/

A lightweight, static web app for exploring MCU peripheral-to-pad mux options and planning board pin assignments. Works on any static host (including GitHub Pages) and offline.

What it does

• Lets you pick a CPU and browse all instance/port pad options
• Optionally pick a board profile to filter to only pads exposed on that board and map pads to board pin numbers
• Prevents selecting conflicting board pins across instances
• Persists selections and hardware choice in localStorage

Getting started

1. Visit the live site: https://ccrome.github.io/microcontroller-pin-selector/
2. Or serve the repository root with any static server and open index.html.
3. Use the header controls to select a Board (optional) and/or CPU.

Repository layout

boards/        # Board definitions (metadata + pad→board pin map)
cpus/          # CPU pin-mux databases
assets/        # UI code and styles
  app.js       # Main application logic
  styles.css   # Styles
index.html     # App shell

Board discovery and format

Boards are discovered via a simple manifest at boards/index.json. The manifest lists file paths only; all descriptive metadata lives in each board file.

boards/index.json example:

{
  "files": [
    "boards/teensy4.1.json"
  ]
}

Each board JSON must include an id, a human-friendly name, the CPU id it targets, and its pad→pin mapping:

{
  "id": "teensy4.1",
  "board": "Teensy 4.1",
  "cpu": "i.mxrt1062",
  "pins": [
    { "pin": 0,  "aliases": [],       "pad": "GPIO_AD_B0_03" },
    { "pin": 1,  "aliases": [],       "pad": "GPIO_AD_B0_02" }
    // ... more pins ...
  ]
}

• id: stable identifier used in the UI
• board: display name
• cpu: must match a CPU id in cpus/index.json
• pins[]: links board pin numbers to MCU pads; optional aliases are display-only

When a board is selected, the app:

• Filters all combos to the set of pads present in the board's pins[]
• Maps a selected pad to one or more board pin numbers for display and conflict detection
• Locks the CPU dropdown to the board's cpu

CPU discovery and format

CPUs are listed in cpus/index.json with an id, name, and the path to their pin database file.

cpus/index.json example:

{
  "cpus": [
    { "id": "i.mxrt1062", "name": "NXP i.MX RT1062", "file": "cpus/i.mxrt1062.pins.json" }
  ]
}

CPU pin database format is a simple nested object:

{
  "LPUART1": {
    "LPUART1_TXD": [["GPIO_AD_B0_12", "ALT2"]],
    "LPUART1_RXD": [["GPIO_AD_B0_13", "ALT2"]]
  },
  "I2C1": {
    "I2C1_SCL": [["GPIO_AD_B1_00", "ALT3"]],
    "I2C1_SDA": [["GPIO_AD_B1_01", "ALT3"]]
  }
}

Shape details:

• Top level keys are peripheral instances (e.g., LPUART1, LPI2C1)
• Each instance has ports (e.g., LPUART1_TXD)
• Each port is an array of [pad, alt] tuples; alt can be "-" if not applicable

Adding a new board

1. Create a new file under boards/ following the Board JSON schema shown above.
2. Add the file path to boards/index.json under files.
3. Ensure the board's cpu id exists in cpus/index.json.

Adding a new CPU

1. Add a new <cpu-id>.pins.json file under cpus/ following the CPU format above.
2. Add an entry to cpus/index.json with the id, name, and file path.

State and clearing

• The app saves boardId, cpuId, the active instance, and all selections to localStorage (pinSelectorState.v1).
• Use the header "Clear selections" button to remove all selections (state updates immediately).

Notes

• This is a static, dependency-free app. No build step is required.
• JSON files are fetched relative to the site root; paths in the manifests should be correct from the deployed root.