Remote Monitoring with GSM Module and STM32

Difficulty Level: Intermediate

This tutorial will guide you through the process of interfacing a GSM module with an STM32 microcontroller. This setup allows for remote data transmission, ideal for IoT projects that need cellular connectivity for monitoring data remotely.

Components Required

• STM32 development board (e.g., STM32F103C8T6)
• GSM module (e.g., SIM800L or SIM900)
• Jumper wires
• STM32CubeIDE
• Power supply for STM32 board and GSM module
• SIM card with active data plan (for GSM module)

Step 1: Wiring the GSM Module

Connect the GSM module to your STM32 board as follows:

GSM Module Pin | STM32 Pin
---------------|-------------
VCC            | 5V or 3.3V (depending on module specs)
GND            | GND
TXD            | RX (e.g., PA10)
RXD            | TX (e.g., PA9)
        

Step 2: Set Up the STM32 Project

1. Open STM32CubeIDE and create a new STM32 project.

2. Configure the USART interface for serial communication with the GSM module:

• Select the USART peripheral (e.g., USART1) and configure it for 9600 baud rate (or as required by your module).
• Set TX and RX pins to the appropriate GPIO pins connected to the GSM module.

3. Initialize the project to include the STM32 HAL library.

Step 3: Set Up GSM Commands

To communicate with the GSM module, you’ll need to use AT commands. The most common commands include:

• AT – Check communication with the module.
• AT+CMGF=1 – Set the SMS message format to text mode.
• AT+CMGS="phone number" – Send an SMS message.

Step 4: Code for Sending Data via GSM

Include the necessary libraries and set up a function to initialize the GSM module and send data:

// Include necessary libraries
#include "stm32f1xx_hal.h"
#include "usart.h" // Include USART library

// Function to initialize GSM module
void GSM_Init() {
    HAL_UART_Transmit(&huart1, (uint8_t*)"AT\r\n", 4, HAL_MAX_DELAY); // Check connection
    HAL_Delay(1000);
    HAL_UART_Transmit(&huart1, (uint8_t*)"AT+CMGF=1\r\n", 11, HAL_MAX_DELAY); // Set SMS mode to text
    HAL_Delay(1000);
}

// Function to send SMS
void GSM_SendSMS(char *phoneNumber, char *message) {
    char command[30];
    sprintf(command, "AT+CMGS=\"%s\"\r\n", phoneNumber); // Set phone number
    HAL_UART_Transmit(&huart1, (uint8_t*)command, strlen(command), HAL_MAX_DELAY);
    HAL_Delay(1000);
    HAL_UART_Transmit(&huart1, (uint8_t*)message, strlen(message), HAL_MAX_DELAY); // Send message
    HAL_UART_Transmit(&huart1, (uint8_t*)"\x1A", 1, HAL_MAX_DELAY); // End of message
    HAL_Delay(3000); // Wait for the message to be sent
}
        

Step 5: Initialize and Test

In your main() function, initialize the GSM module and call GSM_SendSMS() to send an SMS containing monitoring data:

int main(void) {
    HAL_Init(); // Initialize HAL
    SystemClock_Config(); // Configure clock
    MX_USART1_UART_Init(); // Initialize USART for GSM module
    
    GSM_Init(); // Initialize GSM module
    GSM_SendSMS("+1234567890", "Remote monitoring data: Temperature = 25°C"); // Example data
    
    while (1) {
        // Main loop - you can add more data retrieval and sending logic here
    }
}
        

Step 6: Compile and Upload

Compile your project in STM32CubeIDE, ensure there are no errors, and upload the code to your STM32 board. Insert a SIM card into your GSM module and power it on. You should receive an SMS on the specified phone number with the monitoring data.

Conclusion

You have successfully set up remote monitoring using a GSM module with an STM32 microcontroller. This setup can be extended to send various data readings (e.g., temperature, humidity) over SMS for real-time monitoring applications.