Documented wiring and layout

README.md

@@ -1,3 +1,91 @@
 # arduino_gauge_controller
 
-A dedicated gauge controller for Arduinos.
+A dedicated gauge controller for Arduinos.
+
+## Overview
+
+This repository contains:
+
+- `Gaugecontroller/Gaugecontroller.ino`: the Arduino Mega firmware for the stepper gauges, LEDs, and integrated HV5812-based VFD
+- `gauge.py`: the ESP32 / MicroPython MQTT bridge that exposes the controller to Home Assistant
+
+## VFD Support
+
+The integrated gauge controller now includes a 4-digit VFD with:
+
+- 4 alphanumeric digits
+- decimal point indicator
+- alarm bell indicator
+
+On the merged Arduino firmware, the HV5812 control pins are:
+
+- `D46` -> `DATA`
+- `D47` -> `CLOCK`
+- `D48` -> `STROBE`
+- `D49` -> `BLANK/OE`
+
+The standalone VFD sketch used `D51/D52/D53/D49`, but `51/52/53` conflict with the gauge stepper pins in the integrated controller.
+
+## Arduino Serial Commands
+
+The merged Arduino firmware accepts:
+
+- `VFD`
+  clears the display and turns off decimal point and alarm bell
+- `VFD 1234`
+- `VFD 0123`
+- `VFD DEAD`
+- `VFD 8888.`
+- `VFD BEEF!`
+- `VFD 12AF.!`
+
+Rules:
+
+- up to 4 characters are displayed
+- valid characters are `0-9`, `A-F`, and `-`
+- `.` enables the decimal point
+- `!` enables the alarm bell
+- shorter values are right-aligned
+- leading zeroes are preserved if they are part of the input
+
+## Home Assistant Entities
+
+The MQTT bridge publishes Home Assistant discovery entities for the VFD:
+
+- `VFD Display`
+  text entity for the displayed value
+- `VFD Decimal Point`
+  switch entity
+- `VFD Alarm`
+  switch entity
+
+The display is intentionally exposed as a text entity rather than a numeric entity so that:
+
+- leading zeroes are preserved
+- hexadecimal values like `DEAD` or `BEEF` work
+- clearing the display is possible with an empty value
+
+## MQTT Topics
+
+Using the configured `mqtt_prefix` from `config.json`, the VFD topics are:
+
+- `<prefix>/vfd/set`
+- `<prefix>/vfd/state`
+- `<prefix>/vfd/decimal_point/set`
+- `<prefix>/vfd/decimal_point/state`
+- `<prefix>/vfd/alarm/set`
+- `<prefix>/vfd/alarm/state`
+
+Example with the default prefix `gauges`:
+
+- `gauges/vfd/set`
+- `gauges/vfd/decimal_point/set`
+- `gauges/vfd/alarm/set`
+
+Example payloads:
+
+- publish `0123` to `gauges/vfd/set`
+- publish `ON` to `gauges/vfd/decimal_point/set`
+- publish `OFF` to `gauges/vfd/alarm/set`
+
+The MQTT bridge then converts that into the correct Arduino serial command such as `VFD 0123.`.