Calvin 📅

E-ink calendar display for Raspberry Pi Zero. Renders Google Calendar + weather forecast to a PNG + external display without the heavy chromium dependency - only using 2D graphics.

• Inspiration: https://github.com/speedyg0nz/MagInkCal (Thanks!)

Features

• 📅 Month view calendar with current month
• 🌡️ 8-day weather forecast (day/night average temperatures shown in top-right corner of each day)
• 🔋 Battery percentage display (PiSugar 2 integration)
• 🎨 Optimized for Waveshare e-ink displays (4-color: white, black, red, grey)
• 📆 Multi-day events span across all days
• ⏰ Past events displayed in grey
• 🔴 Current/future event times shown in red
• 📦 Single self-contained executable with embedded Liberation Sans fonts (no external dependencies)
• ⚡ Direct graphics rendering using pure Go (no Chrome/Chromium required)

Setup

1. Google Calendar API

1. Go to Google Cloud Console
2. Create project → Enable Google Calendar API
3. Create OAuth client ID (Desktop app)
4. Download JSON → save as credentials.json

2. Build & Run

go mod tidy
go build -o calvin .
cp config.example.yaml config.yaml
# Edit config.yaml with your location

./calvin  # First run opens auth flow

3. Cross-compile for Pi Zero

GOOS=linux GOARCH=arm GOARM=6 go build -o calvin-arm .

4. Systemd Setup (Raspberry Pi)

To run Calvin automatically on boot and handle logging via journald (all stdout/stderr logs will be captured by systemd):

# Copy the service file
sudo cp calvin.service /etc/systemd/system/

# Edit the service file if your installation path differs from /home/pi/calvin
sudo nano /etc/systemd/system/calvin.service

# Reload systemd
sudo systemctl daemon-reload

# Enable the service to start on boot
sudo systemctl enable calvin.service

# Start the service manually (optional)
sudo systemctl start calvin.service

# Check service status
sudo systemctl status calvin.service

View logs:

# View all calvin logs
sudo journalctl -u calvin.service

# Follow logs in real-time
sudo journalctl -u calvin.service -f

# View logs since last boot
sudo journalctl -u calvin.service -b

Config

display:
  width: 1304
  height: 984

weather:
  latitude: 49.9585
  longitude: 14.2888
  timezone: "Europe/Prague"

calendar:
  credentials_file: "credentials.json"
  token_file: "token.json"
  calendars:
    - id: "primary"
      name: "Personal"
  max_events_per_day: 10

output:
  path: "calendar.png"

Error Handling

When errors occur, Calvin automatically generates an error PNG with debugging information at the configured output path. The error image includes:

• Error message
• Timestamp
• Command arguments
• Go version
• OS/Architecture

Commands

./calvin                   # Generate calendar.png, set alarm, shutdown
./calvin --no-shutdown     # Test mode: generate PNG but skip PiSugar alarm/Raspberry Pi shutdown
./calvin --no-battery      # Don't read battery level (shows 100%, useful for local development)
./calvin --list-calendars  # Show available calendars

PiSugar Integration

When running on Raspberry Pi Zero with PiSugar 2:

• Displays battery percentage in the header (e.g., "Battery: 85%")
• Automatically sets alarm for next hour at :00 (e.g., if it's 14:30, alarm set for 15:00)
• Shuts down the system after generating the calendar
• Use --no-shutdown flag for testing without alarm/shutdown
• Use --no-battery flag when running locally without PiSugar hardware

License

MIT