SumiClock

A minimalist clock generator for e-paper displays that brings old Kindles back to life with timezone-aware time, weather, and battery-friendly updates.

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SumiClock

Tagline

Bringing E-paper displays back to life with a minimalist, timezone-aware clock and weather display

Category

Resurrection - Bringing old-generation Kindles and their browser functionality back to life

Inspiration

E-paper displays like Kindle and Kobo e-readers are amazing pieces of technology - they're readable in sunlight, consume almost no power, and can display information indefinitely without electricity. But their experimental web browsers are rarely used, and old-generation e-readers sit forgotten in drawers.

I wanted to resurrect these "dead" devices and revive their underutilized browser functionality by creating something useful: a simple, elegant clock that can run 24/7 on an old Kindle, turning it into a low-power ambient display.

What it does

SumiClock generates clean, high-contrast clock images optimized for E-paper displays. It:

  • Displays current time in any timezone
  • Shows date and optional weather information
  • Automatically switches between light/dark themes based on time of day
  • Supports both landscape and portrait orientations
  • Caches images for fast, efficient serving
  • Runs as a lightweight Docker container

Users can point their E-reader's browser to the SumiClock URL and get a constantly updating, battery-friendly clock display.

How I built it

Technology Stack

  • FastAPI: Lightweight Python web framework for serving images
  • Redis: Caching layer for performance
  • Pillow (PIL): Image generation optimized for E-paper
  • Docker: Containerized deployment
  • OpenWeatherMap API: Weather data integration

Development with Kiro

Kiro was essential to this project's rapid development:

1. Steering Documents Created 7 comprehensive steering documents that taught Kiro about:

  • E-paper display characteristics and optimization
  • Python development standards (Google Style Guide)
  • FastAPI best practices
  • Docker deployment patterns
  • Testing strategies

These steering docs transformed Kiro from a generic assistant into an E-paper display expert.

2. Agent Hooks Implemented 7 automated workflows:

  • Auto-formatting with Black on save
  • Type checking with mypy
  • Linting with flake8
  • Automated testing on file changes
  • Image validation
  • Docker health monitoring
  • Dependency management

These hooks eliminated repetitive tasks and caught errors early.

3. Spec-driven Development For complex features like the SVG template system, I created detailed specifications that Kiro used to generate well-structured, maintainable code.

4. Vibe Coding For simpler features, conversational development with Kiro was incredibly fast:

  • "Add timezone support" → Complete pytz integration
  • "Optimize for E-paper" → Grayscale rendering, high contrast
  • "Add weather display" → API integration + custom E-ink icons

Time Savings

Traditional development: 20-30 hours With Kiro: 6-8 hours Time saved: 70-75%

Challenges I ran into

E-paper Optimization E-paper displays have unique constraints:

  • Slow refresh rates (1-2 seconds)
  • Limited color depth (grayscale)
  • Need for high contrast

Solution: Used PIL's grayscale mode, pure black/white rendering, and aggressive caching to minimize updates.

Font Rendering E-paper displays need clear, readable fonts. Finding and configuring Noto Sans CJK for Japanese character support required careful testing.

Weather Icon Design Standard weather icons don't work well on E-paper. Created custom high-contrast icons specifically designed for E-ink displays.

Timezone Handling Ensuring accurate time display across timezones required careful use of pytz and UTC conversion.

Accomplishments that I'm proud of

  • Minimalist Design: Clean, distraction-free interface perfect for ambient displays
  • E-paper Optimization: Images look crisp and clear on E-ink screens
  • Comprehensive Documentation: 7 steering docs, detailed README, extensive code comments
  • Automated Workflows: 7 agent hooks that streamline development
  • Extensible Architecture: Easy to add new features (electricity usage, calendar, etc.)
  • Docker Deployment: One-command setup with docker-compose

What I learned

E-paper Technology

  • Display characteristics and constraints
  • Optimization techniques for E-ink
  • Device-specific considerations (Kindle vs Kobo)

AI-Assisted Development

  • Steering documents dramatically improve AI responses
  • Agent hooks eliminate repetitive tasks
  • Spec-driven development works well for complex features
  • Vibe coding is perfect for rapid prototyping

Python Best Practices

  • Type hints and mypy for reliability
  • Black for consistent formatting
  • Comprehensive testing strategies
  • Docker for reproducible environments

What's next for SumiClock

Immediate Plans (Before Judging)

  • Add electricity usage display via smart meter API
  • Implement multiple timezone support in single image
  • Create more theme options
  • Add calendar integration

Future Enhancements

  • Custom layout templates
  • Battery-friendly update intervals
  • Support for more E-paper devices
  • Plugin system for custom data sources
  • Web configuration interface
  • MCP integration for external APIs

Long-term Vision

Transform SumiClock into a platform for ambient information displays on E-paper devices, making "obsolete" E-readers useful again as low-power, always-on information displays.

Built With

  • Python
  • FastAPI
  • Redis
  • Docker
  • Pillow (PIL)
  • OpenWeatherMap API
  • Kiro (AI development assistant)

Try it out

Kiro Usage

See KIRO_USAGE.md for detailed documentation on how Kiro accelerated this project's development.

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