Temp-Pressure System

This project is a sensor hub system composed of two parts:

• Client (STM32): Collects environmental and location data.
• Server (ESP32): Receives, validates, and forwards data to an MQTT broker.

Together, they form an IoT pipeline for transmitting sensor readings from the STM32 to a remote MQTT subscriber.

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Project Structure

client/ # STM32 firmware
server/ # ESP32 firmware

Client (STM32)

• Reads temperature and humidity from a DHT22 sensor (single-wire protocol).
• Reads GPS coordinates from NEO-6M GPS module (UART with NMEA sentences).
• Displays sensor values on an I²C screen.
• Sends collected data to ESP32 over UART in JSON format.

Example message format:

{"id":1,"temp":24.56,"hum":61.23,"lat":48.856613,"lon":2.352222}

Server (ESP32)

• Receives JSON messages from STM32 via UART.
• Parses and validates the JSON.
• Connects to Wi-Fi and an MQTT broker.
• Publishes the data to MQTT topics based on sensor ID:

sensors/bluepill/1
sensors/bluepill/unknown

Protocols Used

The system makes use of several communication protocols:

• DHT22 Single-Wire Protocol: for reading temperature and humidity.
• UART: between STM32 and NEO-6M GPS module (NMEA sentences) and between STM32 client and ESP32 server (JSON messages).
• I²C: for STM32 to communicate with the display.
• Wi-Fi: ESP32 connects to a Wi-Fi network to access the broker.
• MQTT: ESP32 publishes sensor data to an MQTT broker.

Getting Started

Requirements

• STM32 board (e.g., Blue Pill) with DHT22, NEO-6M GPS, I²C screen.
• ESP32 development board.
• MQTT broker (e.g., Mosquitto).

Steps

• Flash client/ code onto STM32.
• Flash server/ code onto ESP32.
• Configure Wi-Fi credentials and MQTT broker URL in server/main.c.
• Start your MQTT broker.
• Subscribe to the topic:

mosquitto_sub -h <broker_ip> -t "sensors/bluepill/#" -v

Example Output

When STM32 reads a sample from sensors, you’ll see in MQTT:

sensors/bluepill/1 {"id":1,"temp":24.56,"hum":61.23,"lat":48.856613,"lon":2.352222}

Future Improvements

• Add support for multiple STM32 clients with unique IDs.
• Enable TLS/SSL for MQTT communication.
• Add persistent storage on ESP32 (e.g., SD card).
• Implement OTA (Over-The-Air) updates for ESP32.