WeatherProbe

Solar-powered ESP32 weather station that collects temperature, humidity, pressure, and GPS location every 5 minutes and publishes to GCP Pub/Sub via MQTT over TLS.

Hardware

Component	Part	Interface
MCU	ESP32-WROOM-32 DevKit	--
Environment sensor	BME280	I2C (addr 0x76)
GPS receiver	NEO-M8N	UART @ 9600 baud
Battery	18650 Li-ion 3.7 V	ADC via voltage divider
Solar panel	6 V panel	TP4056 charge controller

Wiring Diagram

graph LR
    subgraph Solar Power
        SOLAR["6 V Solar Panel"] --> TP4056["TP4056\nCharge Controller"]
        TP4056 --> BAT["18650 Li-ion\n3.7 V"]
    end

    BAT --> |VCC / GND| ESP32["ESP32-WROOM-32"]

    subgraph Voltage Divider
        BAT --> R1["R1\n100 k"]
        R1 --> MID((" "))
        MID --> R2["R2\n100 k"]
        R2 --> GND1["GND"]
    end
    MID --> |GPIO34 / ADC1_CH6| ESP32

    subgraph BME280 Sensor
        BME["BME280\nTemp / Hum / Press"]
    end
    ESP32 --> |GPIO21 SDA| BME
    ESP32 --> |GPIO22 SCL| BME

    subgraph GPS Module
        GPS["NEO-M8N\nGPS Receiver"]
    end
    ESP32 --> |GPIO17 TX2| GPS
    GPS --> |GPIO16 RX2| ESP32

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Data Path

graph LR
    ESP32["ESP32"] -->|MQTT / TLS| HMQ["HiveMQ Cloud"]
    HMQ -->|Webhook| CF["GCP Cloud\nFunction"]
    CF -->|Publish| PS["Pub/Sub\nweatherprobe-readings"]
    ESP32 -.->|Offline| SPIFFS["SPIFFS\nRing Buffer"]
    SPIFFS -.->|Drain on reconnect| ESP32

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Wake Cycle

Every 5 minutes the firmware:

1. Reads BME280 (temperature, humidity, pressure) over I2C
2. Reads GPS (latitude, longitude, altitude) over UART -- 30 s timeout, falls back to last-known position stored in RTC memory
3. Reads battery voltage via ADC (16-sample average)
4. Connects WiFi, synchronises time via SNTP
5. Publishes a JSON reading to HiveMQ via MQTT/TLS (QoS 1)
6. Drains up to 10 buffered readings from SPIFFS
7. If publish fails, stores the reading in the SPIFFS ring buffer
8. Enters deep sleep

JSON Payload

{
  "device_id": "weatherprobe-01",
  "ts": 1709380800,
  "temp_c": 22.5,
  "humidity_pct": 45.2,
  "pressure_hpa": 1013.25,
  "lat": 60.1699,
  "lon": 24.9384,
  "alt_m": 15.3,
  "battery_pct": 78,
  "battery_v": 3.82,
  "gps_fix": true
}

Project Structure

ard_weatherprobe/
├── CMakeLists.txt          Project-level CMake
├── Makefile                Convenience wrapper for idf.py
├── sdkconfig.defaults      ESP-IDF Kconfig defaults
├── partitions.csv          Custom partition table (NVS + SPIFFS)
├── provision.sh            Interactive credential provisioning
├── main/
│   ├── CMakeLists.txt      Component source list
│   ├── main.c              Entry point and wake-cycle orchestration
│   ├── config.h            Pin assignments, timing, buffer limits
│   ├── sensor_bme280.c/h   BME280 I2C driver with Bosch compensation
│   ├── sensor_gps.c/h      NEO-M8N UART NMEA GGA parser
│   ├── battery.c/h         ADC battery voltage monitor
│   ├── data_buffer.c/h     SPIFFS FIFO ring buffer
│   ├── credentials.c/h     NVS credential loader
│   └── wp_mqtt.c/h         WiFi STA + MQTT/TLS client
└── cloud/
    ├── cloud_function/
    │   ├── main.py         GCP Cloud Function (MQTT webhook -> Pub/Sub)
    │   └── requirements.txt
    └── pubsub_setup.sh     Create Pub/Sub topic and subscription

Build

Requires the ESP-IDF toolchain (v5.x).

# Build
make build

# Flash and monitor (most common)
make fm

# Override serial port
make flash PORT=/dev/ttyACM0

# Provision WiFi and MQTT credentials to NVS
make provision

# Other targets: clean, fullclean, menuconfig, size, erase

Or use idf.py directly:

idf.py build
idf.py -p /dev/ttyUSB0 flash monitor

Provisioning

Before first use, flash WiFi and MQTT credentials into the NVS partition:

./provision.sh

The script prompts for WiFi SSID/password and MQTT broker details, then writes them to the ESP32's NVS flash. Credentials never appear in source code.

Cloud Setup

1. Create the Pub/Sub topic and subscription:

   cd cloud && bash pubsub_setup.sh

2. Deploy the Cloud Function:

   cd cloud/cloud_function
   gcloud functions deploy weatherprobe-bridge \
       --runtime python312 \
       --trigger-http \
       --entry-point webhook \
       --set-env-vars GCP_PROJECT=<project>,WEBHOOK_SECRET=<secret>

3. Configure HiveMQ Cloud to forward messages to the Cloud Function URL.

License

MIT