How to Use SIM800L GSM module (with external antenna + SIM card): Examples, Pinouts, and Specs

The SIM800L GSM module is a compact and versatile GSM/GPRS module designed for communication over cellular networks. It supports SMS, voice calls, and data transmission, making it ideal for IoT applications, remote monitoring, and mobile communication projects. Equipped with an external antenna, the module ensures improved signal strength and reliable connectivity. A SIM card is required to access the cellular network.

• IoT devices for remote monitoring and control
• SMS-based alert systems
• GPS tracking systems (when paired with a GPS module)
• Home automation and security systems
• Voice call-enabled projects
• Data logging and transmission over GPRS

• Operating Voltage: 3.7V to 4.2V (recommended: 4.0V)
• Operating Current: 0.2A (idle), up to 2A (transmission)
• Frequency Bands: Quad-band 850/900/1800/1900 MHz
• Communication Protocols: GSM, GPRS (Class 12)
• SIM Card Support: Micro SIM
• Antenna: External antenna (included)
• Serial Communication: UART (default baud rate: 9600 bps)
• Dimensions: 25mm x 23mm x 3mm

The SIM800L module has 8 pins. Below is the pinout and description:

1. Power Supply:

   • Use a stable power source capable of providing 3.7V to 4.2V with at least 2A current.
   • A LiPo battery or a DC-DC buck converter is recommended. Avoid powering the module directly from a 5V source, as it may damage the module.

2. Connections:

   • Connect the VCC and GND pins to the power supply.
   • Connect the TXD pin of the module to the RX pin of the microcontroller (e.g., Arduino).
   • Connect the RXD pin of the module to the TX pin of the microcontroller.
   • Attach the external antenna to the ANT connector.
   • Insert a micro SIM card into the SIM slot.

3. Initialization:

   • Use AT commands to configure and control the module.
   • Ensure the baud rate of the microcontroller matches the module's default baud rate (9600 bps).

4. Example Circuit:
   Below is a basic connection diagram for the SIM800L module with an Arduino UNO:

   • SIM800L TXD → Arduino RX (Pin 0)
   • SIM800L RXD → Arduino TX (Pin 1)
   • SIM800L VCC → 3.7V to 4.2V power source
   • SIM800L GND → Arduino GND

#include <SoftwareSerial.h>

// Define RX and TX pins for SoftwareSerial
SoftwareSerial SIM800L(10, 11); // RX = Pin 10, TX = Pin 11

void setup() {
  // Initialize serial communication with the SIM800L module
  SIM800L.begin(9600); // Default baud rate of SIM800L
  Serial.begin(9600);  // Serial monitor for debugging

  // Wait for the module to initialize
  delay(1000);
  Serial.println("Initializing SIM800L...");

  // Send an AT command to check communication
  SIM800L.println("AT");
  delay(1000);

  // Read and print the response from the module
  while (SIM800L.available()) {
    Serial.write(SIM800L.read());
  }
}

void loop() {
  // Example: Send an SMS
  if (Serial.available()) {
    String command = Serial.readString();

    if (command == "sendSMS") {
      SIM800L.println("AT+CMGF=1"); // Set SMS mode to text
      delay(1000);

      SIM800L.println("AT+CMGS=\"+1234567890\""); // Replace with recipient's number
      delay(1000);

      SIM800L.println("Hello, this is a test SMS from SIM800L!"); // SMS content
      delay(1000);

      SIM800L.write(26); // Send Ctrl+Z to send the SMS
      delay(5000);

      Serial.println("SMS sent!");
    }
  }
}

• Power Supply: Ensure a stable power source with sufficient current (2A) to prevent unexpected resets or malfunctions.
• Antenna Placement: Position the external antenna away from interference sources for optimal signal strength.
• SIM Card: Use an active SIM card with sufficient balance or data plan. Ensure the SIM card is properly inserted.
• UART Voltage Levels: The SIM800L operates at 3.3V logic levels. Use a voltage divider or level shifter if connecting to a 5V microcontroller.
• Network Compatibility: Verify that the module supports the frequency bands of your local cellular network.

1. Module Not Responding to AT Commands:

   • Check the power supply voltage and current.
   • Verify the TX and RX connections between the module and microcontroller.
   • Ensure the baud rate matches (default: 9600 bps).

2. Frequent Resets or Unstable Operation:

   • Use a power source capable of providing at least 2A current.
   • Add a capacitor (e.g., 1000µF) across the power supply to stabilize voltage.

3. No Network Connection:

   • Ensure the SIM card is active and has sufficient balance.
   • Check the antenna connection and position it for better signal reception.
   • Verify that the module supports the frequency bands of your network.

4. SMS Not Sending:

   • Confirm the recipient's phone number is in the correct format (e.g., +).
   • Ensure the module is in SMS text mode (AT+CMGF=1).

• Q: Can the SIM800L module be powered directly from a 5V source?
  A: No, the module requires a voltage between 3.7V and 4.2V. Use a step-down converter or LiPo battery.

• Q: How do I reset the module?
  A: Pull the RST pin LOW for at least 100ms, then release it.

• Q: What is the default baud rate of the SIM800L?
  A: The default baud rate is 9600 bps.

• Q: Can the SIM800L be used for internet access?
  A: Yes, the module supports GPRS for data transmission. Use AT commands to configure GPRS settings.