Initial pass on the design documentation.

The design doc and software design doc.
The UML images are generated with plantUML from the *.puml files.

docs/design.md

@@ -0,0 +1,76 @@
+# Design Document: MicroBadge
+
+## Overview
+
+**MicroBadge** is an interactive embedded application built for the BBC
+micro:bit v2. It is written in **Rust** using the **Embassy** async embedded
+runtime. The project functions as a **conference name badge** that acts as a
+professional and technical icebreaker at events.
+
+The application framework includes:
+* A **menu system** for switching between apps.
+* A **name scroller** for displaying your name or custom message.
+* A **Snake game** for fun and interactivity.
+* A **NFC business card** app for sharing contact info. **Still in progress**
+
+## Goals
+
+* Provide a custom and memorable name badge experience.
+* Showcase embedded Rust development using async and no-std.
+* Enable fun interactions and sharing via NFC.
+* Serve as a technical portfolio piece for conferences, meetings, and
+  interviews.
+
+## Architecture
+
+### 1. Core Framework
+
+* Built on **Embassy** for asynchronous concurrency.
+* Uses hardware abstraction layers (HALs) for GPIO, timers, display, and
+  buttons.
+* Implements a lightweight app-switcher system with a menu UI.
+
+### 2. Applications
+
+#### Name Scroller
+* Scrolls a name or message across the LED matrix.
+* Configurable for speed and repeat mode.
+* Useful for identifying the wearer at a glance.
+
+#### Snake Game
+* Classic Snake game rendered on the 5x5 LED display.
+* Uses `Button A` and `Button B` for turning.
+* Includes food spawning, score tracking, and difficulty selection.
+* Uses PWM for different intensity led lights.
+
+#### NFC Business Card (WIP)
+* Leverages the onboard NFC peripheral.
+* Intends to share vCard/contact data over NFC.
+* Targeted at mobile phones for quick transfer of contact info
+
+## User Interaction
+
+* Navigation is handled via micro:bit's `Button A`, `Button B`, and long-press `Start` gesture
+* LED matrix provides visual feedback for game states and menu navigation
+* Apps are selected from a simple menu UI
+* Snake game is tuned to a slower speed (~4Hz) for usability
+
+## Development Environment
+
+* Written entirely in **Rust**, `#![no_std]`
+* Uses **Embassy** for async device access and task scheduling
+* Debugging output via `defmt`
+* Built and flashed using `probe-rs` and `cargo-embed`
+
+## Future Improvements
+
+* Finalize NFC vCard transmission
+* Add configuration storage via flash memory
+* Create a desktop companion app for editing settings
+* Support BLE for data sync or configuration
+
+## Summary
+
+MicroBadge combines a fun hardware platform with modern Rust development.
+It serves not only as a name badge but also as a way to demonstrate embedded
+skills, share contact info, and invite technical discussion at events.