Weathergotchi: An Open-Source Climate Tamagotchi

Project Overview: The Weathergotchi (officially the E-Paper Climate Logger) is a battery-operated, open-source device designed to track ambient temperature and humidity. It utilizes an always-on e-paper screen to show real-time data and historical trends, storing all readings in non-volatile memory.

🚀 Key Capabilities

The device is engineered for extreme efficiency, capable of running for over one week on a single small Li-Po battery.

The project is fully transparent; all hardware schematics, PCB layouts, firmware, and CAD files are available for public use. For a visual guide, check out the E-Paper Climate Logger YouTube video.

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📂 Repository Architecture

The project is organized into the following directory structure:

E-Paper-Climate-Logger/
├── CAD/        # OpenSCAD source & STL exports
├── PCB/        # KiCad designs, schematics, & datasheets
├── firmware/   # PlatformIO project (Arduino framework)
├── LICENSE     # Legal terms
└── README.md   # Project documentation

Detailed Breakdown

• CAD: Contains parametric models for the enclosure. By modifying constants.scad, users can adjust the physical dimensions of the case.
• PCB: Houses the templog_mainboard files. This includes .kicad_sch and .kicad_pcb files, along with reference designs from Waveshare and SparkFun. Note: KiCad 9 or newer is required.
• Firmware: An ESP32-S3 project managing the I2C bus, SPI display, and power states. Detailed flashing steps are located in firmware/README.md.

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🛠️ Getting Started

Hardware Checklist

• Assembled templog_mainboard (Reflow soldering recommended for SMD parts)
• 1.54-inch e-paper display (Waveshare compatible)
• 3D-printed housing (from CAD/export/)
• Single-cell Li-Po battery ($\approx 400\text{ mAh}$)
• USB-C cable

Software Deployment

1. Install the PlatformIO Core (or the VS Code extension).
2. Upload the code using the following command: pio run --target upload
3. (Optional) View logs via: pio device monitor

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⚡ Hardware & Power Logic

System Architecture

The device utilizes a shared I2C bus for the SHT45, DS3231, 24LC512, and BQ27441. The display is handled via SPI, and the system power is toggled via an LTC2954 soft-button and BQ24075 charger.

The Low-Power Cycle

The device minimizes energy consumption using a strict wake-sleep loop:

Power Metrics:

• Sleep Current: $< 20\text{ }\mu\text{A}$
• Active Burst: $\approx 50\text{ mA}$ for $\approx 400\text{ ms}$
• Wake Interval: Default is $1\text{ minute}$

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⚠️ Known Issues & Limitations

Battery & Power

• Perfect SOC Accuracy $\rightarrow$ The reported battery state of charge is currently inaccurate.
• Critical Low Battery: At $\approx 3.4\text{V}$, the device may enter an unrecoverable state.
  • Fix: Disconnect battery $\rightarrow$ External charge $\rightarrow$ Reconnect. (Likely due to low-quality cells).

Environmental & Hardware

• Thermal Interference: The ESP32 generates heat during activity. To mitigate this, the firmware triggers the SHT45 reading immediately upon waking.
  • Warning: Holding the device or browsing menus will skew readings for several minutes.
• Temperature Floor: The e-paper screen is rated for $T > 0^\circ\text{C}$.
  • Behavior: Logging continues in the background, but the display will not update until it warms up.
• Connectivity: $\text{No Wi-Fi/Bluetooth}$ is included to ensure maximum battery longevity.

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🤝 Contributing

Contributions are welcome! Please submit issues or pull requests following the established project guidelines.