ESP32 Weather Station

A lightweight weather monitoring system that tracks temperature, humidity, air quality, and provides camera snapshots — using an ESP32, MQTT, and a simple web client.

Overview

This project uses an ESP32 device equipped with:

• A camera (OV5640)
• A temperature and humidity sensor (DHT11)
• An air quality sensor (MQ-135)
• A passive buzzer

The ESP32 currently connects to the local Wi-Fi network and communicates via my own MQTT broker, providing access to real-time weather data and user-triggered updates. Soon it will transition to using a SIM7670 3G module for cellular connectivity.

MQTT Interface

Discovery

ESP32 publishes a JSON list of currently available sensors to esp32/available_sensors topic.

Example payload:

[
  { "name": "temp", "type": "text/plain" },
  { "name": "humidity", "type": "text/plain" },
  { "name": "air_quality", "type": "text/plain" },
  { "name": "camera", "type": "image/jpeg" }
]

Clients subscribe to this topic on connect and use the metadata to dynamically render controls and correctly display responses.

Requesting Sensor Data

The web client sends requests to esp32/request/<sensorName> topic.

The <sensorName> must match one of the available sensors.

Example:

esp32/request/camera      → triggers a new photo capture  
esp32/request/humidity    → triggers humidity reading  
esp32/request/air_quality → triggers air quality percentage
esp32/request/temp        → triggers temperature reading

ESP32 will buzz once to confirm reception of any valid or invalid request.

Receiving Sensor Data

ESP32 publishes sensor results to esp32/response/<sensorName> topic.

• Topic pattern: esp32/response/
• Payload: Value returned by the sensor

Example payloads:

esp32/response/temp: "23.5"
esp32/response/humidity: "69.6"
esp32/response/air_quality: "47"
esp32/response/camera: (Base64-encoded JPEG string)

Error Handling

Any malformed requests, unavailable sensors, or failures are published to esp32/response/error topic.

Example payload:

sensor_unknown:airflow
invalid_topic:bad/request/humidity

💻 Web Client

The frontend is a static HTML + JavaScript page that:

• Connects to the MQTT broker via WebSocket
• Subscribes to esp32/available_sensors and esp32/response/# topics
• Renders one button per available sensor using metadata from available_sensors
• Sends requests via MQTT on button click
• Displays each result dynamically based on the sensor type (text/plain or image/jpeg)

The client is fully decoupled from the ESP32 implementation. It relies exclusively on metadata provided via MQTT.

Development & Testing

All ESP32 code is developed using Test-Driven Development (TDD) with separation of logic and hardware:

• Business logic is tested with PlatformIO’s native environment
• ESP32-specific components are tested in esp32 integration tests
• All sensors are represented by test doubles (fakes/stubs) for isolated testing
• Sensor registry, MQTT dispatch, message structure, and system boot logic are tested without hardware

ESP32 GPIO Usage Overview

GPIO	Status	Used By	Purpose / Notes
0	⚠️ Avoid	Boot pin	Must be pulled LOW to enter flash mode
1	⚠️ UART TX	Serial	TX0 — used for programming/debug
2	⚠️ Avoid	Boot pin	Must be LOW on boot; often used for onboard LED
3	⚠️ UART RX	Serial	RX0 — used for programming/debug
4	❌ Occupied	Camera	D0
5	❌ Occupied	Camera	D1
12	⚠️ Caution	-	Must be LOW on boot — strapping pin
13	❌ Occupied	ADC2	WiFi uses ADC2, so no reading when WiFi=on (will be freed when switching to 3G)
14	❌ Occupied	Buzzer	Passive buzzer signal
15	✅ Free	-	Often used for SPI CS
16	✅ Free	-	Can be used; UART2 RX
17	✅ Free	-	Can be used; UART2 TX
18	❌ Occupied	Camera	D2
19	❌ Occupied	Camera	D3
21	❌ Occupied	Camera	XCLK
22	❌ Occupied	Camera	PCLK
23	❌ Occupied	Camera	HREF
25	❌ Occupied	Camera	VSYNC
26	❌ Occupied	Camera	SCCB SDA
27	❌ Occupied	Camera	SCCB SCL
32	❌ Occupied	MQ-135	MQ-135 Air Quality sensor
33	❌ Occupied	DHT11	Temp & humidity sensor
34	❌ Occupied	Camera	D6 (input only)
35	❌ Occupied	Camera	D7 (input only)
36	❌ Occupied	Camera	D4 (input only)
39	❌ Occupied	Camera	D5 (input only)

✅ Legend:

• ✅ Free – safe to use for sensors/peripherals
• ❌ Occupied – already used here
• ⚠️ Caution / Avoid – avoid unless really sure