[FEATURE] LCD v9: Weather forecast, AQI index, animated transitions

[farcomiot]

📺 LCD v9: Weather Forecast, AQI Index & Animated Transitions

Current State (LCD v8)

• 14-screen rotation: 11 sensor bars + info + logo + health
• SPI @ 32 MHz, ~6.7 FPS refresh
• Proximity-based screen switching (LTR559, threshold 800)
• Static screens with color bars

Proposed Features

Weather Forecast Screen

• OpenWeatherMap API integration — fetch 3-day forecast via WiFi
• Weather icons — programmatic sun/cloud/rain/storm drawings (PIL)
• Min/max temperature for today + tomorrow
• Humidity forecast comparison with local BME280
• Cache forecast data — refresh every 30 minutes, display cached between refreshes
• API key management — store in .env file on Pi (see [SECURITY] Pi hardening: firewall, fail2ban, SSH keys #3)

AQI Index Screen

• EPA AQI calculation from PM2.5 readings using standard breakpoints
• Color-coded AQI gauge — Green (Good) → Maroon (Hazardous)
• AQI category label — "Good", "Moderate", "USG", "Unhealthy", "Very Unhealthy", "Hazardous"
• 24h average PM2.5 from SQLite for AQI accuracy (instantaneous vs rolling)
• Health recommendation text — "Enjoy outdoors" / "Sensitive groups limit exposure"

Animated Transitions

• Slide transitions between screens (left-to-right wipe)
• Fade effect using alpha blending on screen switch
• Loading animation for boot splash (spinning ruedita)
• Smooth bar graph updates — interpolate between old and new values

Technical Approach

Weather API

# OpenWeatherMap free tier: 1000 calls/day
# At 30-min refresh = 48 calls/day (well within limit)
URL: api.openweathermap.org/data/2.5/forecast
Params: lat=25.644&lon=-100.236&units=metric&cnt=8

AQI Breakpoints (EPA Standard)

AQI	PM2.5 (µg/m³)	Category	Color
0-50	0.0-12.0	Good	Green
51-100	12.1-35.4	Moderate	Yellow
101-150	35.5-55.4	USG	Orange
151-200	55.5-150.4	Unhealthy	Red
201-300	150.5-250.4	Very Unhealthy	Purple
301-500	250.5-500.4	Hazardous	Maroon

Animation Performance

• ST7735 @ 32 MHz SPI can handle ~20 FPS full-screen
• Transition frames: 5-8 frames over 0.3s
• Use PIL Image.blend() for alpha transitions
• Pre-render next screen in background thread

Dependencies

• requests library for weather API
• OpenWeatherMap free API key
• Existing PIL/Pillow for animations
• SQLite 24h data for rolling AQI average

Screen Count After v9

Current: 14 screens → Proposed: 16 screens (+weather, +AQI)

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Ref: #1 Roadmap — LCD Enhancements