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Psychrometer — Project History

Milestone log for the Psychrometer project. Records key decisions, structural changes, and completed phases.

2026-06-29

Project inception

  • Revived a shelved concept: miniature low-power autonomous T/H sensors.
  • Concept reviewed; architecture fixed as a star network of battery nodes reporting to one hub.

Concept decisions

  • Node MCU: MSP430G2553 (ultra-low power, deep sleep between cycles).
  • Sensor: BME280 (temperature / humidity / pressure) — chosen over AM2320 for accuracy, low sleep current, and bonus pressure data.
  • Radio: nRF24L01+ via GT-24-Mini module (2.4 GHz, SPI, 3.3 V supply and logic). Wi-Fi rejected — too power-hungry for coin/AA battery life.
  • Topology: star, up to 20 nodes (~10 planned + expansion).
  • Range: apartment / small house — LoRa unnecessary.
  • Period: 10 minutes for indoor and outdoor nodes.
  • Hub: STM32F103C8T6 + LCD; collects and displays only, no network uplink.
  • Outdoor node: powered from 5.28 V / 0.37 W solar panel.

Documentation

  • README.md, requirements.md, HISTORY.md, CHANGELOG.md created.
  • Directory structure agreed: inc/, src/, docs/.