ESP32 SIM900 / SIM900A GSM/GPRS Module

Code Examples

Below you can find code examples of SIM900 / SIM900A GSM/GPRS Module with ESP32 in several frameworks:

• Arduino IDE
• ESP-IDF
• ESPHome
• PlatformIO
• MicroPython

If you encounter issues while using the SIM900 / SIM900A GSM/GPRS Module, check the Common Issues Troubleshooting Guide.

ESP32 SIM900 / SIM900A Arduino IDE Code Example

Example in Arduino IDE

Fill in your main Arduino IDE sketch file with the following code to use the SIM900 / SIM900A GSM/GPRS Module:

#include <SoftwareSerial.h>

SoftwareSerial sim900(10, 11); // RX, TX
#define PWRKEY 9

void powerOnSIM900() {
    pinMode(PWRKEY, OUTPUT);
    digitalWrite(PWRKEY, LOW);
    delay(1000); // Hold PWRKEY low for 1 second
    digitalWrite(PWRKEY, HIGH);
    delay(5000); // Wait for the module to initialize
}

void setup() {
    Serial.begin(9600);
    sim900.begin(9600);
    powerOnSIM900();

    // Test AT command
    sim900.println("AT");
    delay(1000);
    while (sim900.available()) {
        Serial.write(sim900.read());
    }

    // Set SMS text mode
    sim900.println("AT+CMGF=1");
    delay(1000);
    while (sim900.available()) {
        Serial.write(sim900.read());
    }

    // Send SMS
    sim900.println("AT+CMGS=\"+1234567890\""); // Replace with recipient's number
    delay(1000);
    sim900.print("Hello from SIM900");
    sim900.write(26); // CTRL+Z to send
    delay(5000);
    while (sim900.available()) {
        Serial.write(sim900.read());
    }
}

void loop() {
    // Add code to handle incoming messages or other functionalities
}

This Arduino sketch interfaces with the SIM900 module using the SoftwareSerial library. The module is powered on by toggling the PWRKEY pin (GPIO9). An AT command is sent to test communication. The module is configured to SMS text mode using the AT+CMGF command, and an SMS is sent to a specified recipient using AT+CMGS. The message content is terminated with CTRL+Z (ASCII 26) to send the SMS. Additional functionality, such as reading incoming messages or handling data, can be added in the loop.

Connect your ESP32 to your computer via a USB cable, Ensure the correct Board and Port are selected under Tools, Click the "Upload" button in the Arduino IDE to compile and upload the code to your ESP32.

ESP32 SIM900 / SIM900A ESP-IDF Code Example

Example in Espressif IoT Framework (ESP-IDF)

If you're using ESP-IDF to work with the SIM900 / SIM900A GSM/GPRS Module, here's how you can set it up and read data from the sensor. Fill in this code in the main ESP-IDF file:

#include <stdio.h>
#include "driver/uart.h"
#include "driver/gpio.h"
#include "freertos/task.h"

#define TX_PIN 17
#define RX_PIN 16
#define PWRKEY_PIN 4
#define UART_PORT UART_NUM_1

void init_uart() {
    uart_config_t uart_config = {
        .baud_rate = 9600,
        .data_bits = UART_DATA_8_BITS,
        .parity = UART_PARITY_DISABLE,
        .stop_bits = UART_STOP_BITS_1,
        .flow_ctrl = UART_HW_FLOWCTRL_DISABLE
    };

    uart_param_config(UART_PORT, &uart_config);
    uart_set_pin(UART_PORT, TX_PIN, RX_PIN, UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE);
    uart_driver_install(UART_PORT, 1024, 0, 0, NULL, 0);
}

void power_on_sim900() {
    gpio_set_direction(PWRKEY_PIN, GPIO_MODE_OUTPUT);
    gpio_set_level(PWRKEY_PIN, 0);
    vTaskDelay(1000 / portTICK_PERIOD_MS); // Hold PWRKEY low for 1 second
    gpio_set_level(PWRKEY_PIN, 1);
    vTaskDelay(5000 / portTICK_PERIOD_MS); // Wait for the module to initialize
}

void app_main(void) {
    init_uart();
    power_on_sim900();

    char *test_cmd = "AT\r\n";
    uart_write_bytes(UART_PORT, test_cmd, strlen(test_cmd));

    while (true) {
        char data[128];
        int len = uart_read_bytes(UART_PORT, data, sizeof(data), 100 / portTICK_PERIOD_MS);
        if (len > 0) {
            data[len] = '\0';
            printf("Response: %s\n", data);
        }
        vTaskDelay(1000 / portTICK_PERIOD_MS);
    }
}

This ESP-IDF example initializes UART communication with the SIM900 module and powers it on using the PWRKEY pin (GPIO4). The UART interface is configured with GPIO17 as TX and GPIO16 as RX. An AT command is sent to test communication, and responses from the module are printed to the console. This code can be extended to handle SMS, GPRS, or other functionalities provided by the SIM900 module.

Update the I2C pins (I2C_MASTER_SDA_IO and I2C_MASTER_SCL_IO) to match your ESP32 hardware setup, Use idf.py build to compile the project, Use idf.py flash to upload the code to your ESP32.

ESP32 SIM900 / SIM900A ESPHome Code Example

Example in ESPHome (Home Assistant)

Fill in this configuration in your ESPHome YAML configuration file (example.yml) to integrate the SIM900 / SIM900A GSM/GPRS Module

uart:
  tx_pin: GPIO17
  rx_pin: GPIO16
  baud_rate: 9600

switch:
  - platform: gpio
    name: "SIM900 Power"
    pin:
      number: GPIO4
      inverted: true

switch:
  - platform: template
    name: "Send AT Command"
    turn_on_action:
      - uart.write: "AT\r\n"

sensor:
  - platform: custom
    lambda: |-
      return {nullptr};
    sensors:
      - name: "SIM900 Response"

This ESPHome configuration sets up UART communication with the SIM900 using GPIO17 (TX) and GPIO16 (RX) at 9600 baud. A GPIO-based switch is used to control the PWRKEY pin (GPIO4) for powering the module on or off. A template switch allows sending the AT command, and a custom sensor can be implemented to process responses from the module. Additional configurations can be added for SMS or data functionalities.

Upload this code to your ESP32 using the ESPHome dashboard or the esphome run command.

ESP32 SIM900 / SIM900A PlatformIO Code Example

Example in PlatformIO Framework

For PlatformIO, make sure to configure the platformio.ini file with the appropriate environment and libraries, and then proceed with the code.

Configure platformio.ini

First, your platformio.ini should look like below. You might need to include some libraries as shown. Make sure to change the board to your ESP32:

[env:sim900]
platform = espressif32
board = esp32dev
framework = arduino
monitor_speed = 115200

ESP32 SIM900 / SIM900A PlatformIO Example Code

Write this code in your PlatformIO project under the src/main.cpp file to use the SIM900 / SIM900A GSM/GPRS Module:

#include <HardwareSerial.h>
#include <Arduino.h>

HardwareSerial sim900(1);
#define PWRKEY 4

void power_on_sim900() {
    pinMode(PWRKEY, OUTPUT);
    digitalWrite(PWRKEY, LOW);
    delay(1000); // Hold PWRKEY low for 1 second
    digitalWrite(PWRKEY, HIGH);
    delay(5000); // Wait for initialization
}

void setup() {
    Serial.begin(115200);
    sim900.begin(9600, SERIAL_8N1, 16, 17); // RX, TX
    power_on_sim900();

    // Test AT command
    sim900.println("AT");
    delay(1000);
    while (sim900.available()) {
        Serial.write(sim900.read());
    }

    // Send SMS
    sim900.println("AT+CMGF=1"); // Set SMS to text mode
    delay(1000);
    sim900.println("AT+CMGS=\"+1234567890\""); // Replace with recipient's number
    delay(1000);
    sim900.print("Hello from SIM900");
    sim900.write(26); // CTRL+Z to send SMS
    delay(5000);
}

void loop() {
    // Handle incoming data or other functionalities
}

This PlatformIO code interfaces with the SIM900 module using HardwareSerial on an ESP32. The `power_on_sim900` function toggles the PWRKEY pin (GPIO4) to activate the module. The AT command is sent to test communication, and SMS functionality is implemented in the setup. Additional functionalities like GPRS or data handling can be added in the loop.

Upload the code to your ESP32 using the PlatformIO "Upload" button in your IDE or the pio run --target upload command.

ESP32 SIM900 / SIM900A MicroPython Code Example

Example in Micro Python Framework

Fill in this script in your MicroPython main.py file (main.py) to integrate the SIM900 / SIM900A GSM/GPRS Module with your ESP32.

from machine import UART, Pin
import time

# Initialize UART
uart = UART(2, baudrate=9600, tx=17, rx=16)
pwrkey = Pin(4, Pin.OUT)

def power_on_sim900():
    pwrkey.value(0)
    time.sleep(1)  # Hold PWRKEY low for 1 second
    pwrkey.value(1)
    time.sleep(5)  # Wait for module to initialize

def send_at(command):
    uart.write(command + '\r\n')
    time.sleep(1)
    while uart.any():
        print(uart.read().decode('utf-8'), end='')

# Power on the module
power_on_sim900()

# Test communication
send_at('AT')

# Send SMS
send_at('AT+CMGF=1')  # Set SMS to text mode
send_at('AT+CMGS="+1234567890"')  # Replace with recipient's number
uart.write("Hello from MicroPython" + chr(26))

This MicroPython code communicates with the SIM900 module over UART. The `power_on_sim900` function activates the module using the PWRKEY pin (GPIO4). The `send_at` function sends AT commands and prints the responses. The script initializes the module, tests communication, and demonstrates how to send an SMS. Additional logic for handling GPRS data or incoming messages can be added.

Upload this code to your ESP32 using a MicroPython-compatible IDE, such as Thonny, uPyCraft, or tools like ampy.