Design and Implementation of a Smart Home System Based on STM32

1. Overview

A Smart Home System using STM32 microcontrollers enables automation and remote control of home appliances, security, lighting, and environmental monitoring. This project integrates sensors, wireless communication, and a user interface for centralized control.

2. System Architecture

The system consists of:

• STM32 Microcontroller (e.g., STM32F103C8T6 or STM32F407VG)

• Sensors (Temperature, Humidity, Motion, Gas, Light)

• Actuators (Relays, Servo Motors, LEDs)

• Wireless Communication (Wi-Fi, Bluetooth, Zigbee, or LoRa)

• User Interface (Mobile App, Web Dashboard, or Touchscreen LCD)

Block Diagram

+-------------------+       +-------------------+       +-------------------+
|                   |       |                   |       |                   |
|   STM32 MCU       |<----->|   Sensors         |<----->|   Actuators       |
|   (Main Control)  |       |   (Temp, Motion)  |       |   (Relays, LEDs)  |
+-------------------+       +-------------------+       +-------------------+
        ^                                                      ^
        |                                                      |
        v                                                      v
+-------------------+                               +-------------------+
|   Wireless Module |                               |   User Interface  |
|  (Wi-Fi/Bluetooth)|                               |   (Mobile/Web)    |
+-------------------+                               +-------------------+

3. Hardware Components

3.1 STM32 Microcontroller

• STM32F103C8T6 (Blue Pill, cost-effective) or STM32F407VG (more powerful)

• Features:

  • Multiple GPIOs for sensors and actuators

  • ADC for analog sensors (temperature, gas)

  • PWM for motor/servo control

  • UART/I2C/SPI for communication

3.2 Sensors

3.3 Actuators

3.4 Wireless Communication

• Wi-Fi (ESP8266/ESP32) – Connects to cloud (Blynk, MQTT)

• Bluetooth (HC-05/HC-06) – Local smartphone control

• Zigbee (XBee) – Low-power mesh networking

• LoRa (RA-02) – Long-range IoT applications

3.5 Power Supply

• 5V/3.3V Regulator (LM7805/AMS1117)

• Battery Backup (18650 Li-ion + TP4056 Charger)

4. Software Implementation

4.1 Firmware Development (STM32CubeIDE)

• STM32 HAL Library for peripheral configuration

• FreeRTOS (optional, for multitasking)

• Communication Protocols:

  • UART (for Bluetooth/Wi-Fi modules)

  • I2C/SPI (for sensors like BMP280)

  • MQTT/HTTP (for cloud connectivity)

4.2 Key Functions

1. Sensor Data Acquisition

// Read Temperature & Humidity (DHT11)
void DHT11_Read(float *temp, float *humidity) {
    // Send start signal
    HAL_GPIO_WritePin(DHT11_GPIO_Port, DHT11_Pin, GPIO_PIN_RESET);
    HAL_Delay(18);
    HAL_GPIO_WritePin(DHT11_GPIO_Port, DHT11_Pin, GPIO_PIN_SET);
    
    // Read 40-bit data
    uint8_t data[5];
    for (int i = 0; i < 5; i++) {
        data[i] = DHT11_ReadByte();
    }
    
    *humidity = data[0];
    *temp = data[2];
}

2. Relay Control (Appliance Switching)

void Control_Relay(uint8_t relay_num, uint8_t state) {
    switch(relay_num) {
        case 1: HAL_GPIO_WritePin(RELAY1_GPIO_Port, RELAY1_Pin, state); break;
        case 2: HAL_GPIO_WritePin(RELAY2_GPIO_Port, RELAY2_Pin, state); break;
    }
}

3. Wireless Communication (Wi-Fi + MQTT)

// Send sensor data to MQTT broker (via ESP8266)
void MQTT_Publish(char *topic, char *payload) {
    char cmd[100];
    sprintf(cmd, "AT+MQTTPUB=0,\"%s\",\"%s\",0,0\r\n", topic, payload);
    HAL_UART_Transmit(&huart1, (uint8_t*)cmd, strlen(cmd), HAL_MAX_DELAY);
}

5. User Interface Options

5.1 Mobile App (Blynk/Home Assistant)

• Blynk (Drag-and-drop IoT dashboard)

• Home Assistant (Open-source home automation)

• Custom Android/iOS App (MIT App Inventor, Flutter)

5.2 Web Dashboard (Node.js + MQTT)

• MQTT Broker (Mosquitto)

• Node-RED (Flow-based programming)

• React.js Dashboard (Real-time monitoring)

5.3 Local Touchscreen (Nextion LCD)

• Nextion HMI for interactive control

• STM32 UART Communication to update display

6. System Workflow

1. Sensors collect data (temperature, motion, gas)

2. STM32 processes data and makes decisions (e.g., turn on fan if hot)

3. Wireless module sends alerts to phone/cloud

4. User controls devices via app/voice (Google Assistant/Alexa)

5. Actuators execute commands (relay turns on light)

7. Enhancements

• Voice Control (Google Assistant/Alexa integration)

• AI-Based Automation (predictive heating/cooling)

• Solar Power Integration (for energy efficiency)

• Facial Recognition Door Lock (OpenCV + STM32)

8. Conclusion

This STM32-based Smart Home System provides:
✅ Remote monitoring & control
✅ Energy efficiency
✅ Security enhancements
✅ Scalability (supports more sensors/actuators)