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🏗️ Architecture

System Overview

┌─────────────────────────────────────────────────────┐
│                  Raspberry Pi                       │
│                                                     │
│  ┌──────────────┐     ┌──────────────────────────┐  │
│  │  bme280.py   │     │      sensor_api.py       │  │
│  │              │     │         (Flask)           │  │
│  │  I²C driver  │◄────│  GET /bme280             │  │
│  │  Calibration │     │  GET /bme280/publish     │  │
│  │  algorithms  │     │  GET /health             │  │
│  └──────┬───────┘     └───────────┬──────────────┘  │
│         │                         │                  │
│         ▼                         ▼                  │
│  ┌──────────────┐     ┌──────────────────────────┐  │
│  │  BME280 chip │     │      MQTT Broker         │  │
│  │  (I²C 0x77)  │     │   (Home Assistant)       │  │
│  └──────────────┘     └──────────────────────────┘  │
└─────────────────────────────────────────────────────┘

Components

bme280.py — I²C Driver

Low-level sensor driver. Handles:

  • Soft reset and NVM copy wait on each read (Bosch SensorAPI spec)
  • Calibration data extraction from EEPROM registers (0x88, 0xA1, 0xE1)
  • Raw data reading from 0xF7 (8 bytes: pressure, temperature, humidity)
  • Bosch compensation algorithms (double-precision floating point)
  • IIR filter configuration via register 0xF5
  • Measurement completion polling via status register 0xF3

sensor_api.py — HTTP API

Flask application exposing three routes:

Route Role
GET /health Service liveness check
GET /bme280 Returns full sensor reading as JSON
GET /bme280/publish Reads sensor and publishes to MQTT broker

All configuration (MQTT credentials, I²C address, Flask port) is loaded from environment variables via python-dotenv.

Data Flow

BME280 chip  ──I²C──►  bme280.py  ──►  sensor_api.py  ──HTTP──►  client (curl / cron)
                                              │
                                         MQTT publish
                                              │
                                              ▼
                                       MQTT Broker
                                              │
                                              ▼
                                      Home Assistant