How to Use SIM900A: Examples, Pinouts, and Specs

The SIM900A is a complete Dual-band GSM/GPRS solution in a compact plug-in module. Featuring an industry-standard interface, the SIM900A delivers GSM/GPRS 900/1800MHz performance for voice, SMS, Data, and Fax in a small form factor and with low power consumption. It is ideal for a wide range of products including IoT devices, system monitoring, and many other communication systems.

• Mobile phones
• IoT devices
• Remote data monitoring
• SMS-based alert systems
• Voice communication systems

• Dual-Band 900/ 1800 MHz
• GPRS multi-slot class 10/8
• GPRS mobile station class B
• Compliant to GSM phase 2/2+
• Class 4 (2 W @ 900 MHz)
• Class 1 (1 W @ 1800MHz)

1. Power Supply: Connect a 3.4V to 4.5V power supply to the VCC and GND pins. Ensure that the power supply can deliver up to 2A during transmission bursts.

2. Serial Communication: Connect the RXD and TXD pins to a microcontroller or computer's UART interface. Remember that the SIM900A operates at TTL logic levels.

3. Antenna: Attach a suitable GSM antenna to the module for proper communication.

4. SIM Card: Insert a SIM card into the SIM card holder.

• Ensure that the power supply is stable and can handle the current requirements.
• Use a level shifter if the microcontroller operates at a different logic level than the SIM900A.
• Place the antenna away from metal objects and electronic devices to minimize interference.
• Follow all ESD precautions when handling the module to prevent damage.

#include <SoftwareSerial.h>

SoftwareSerial SIM900A(7, 8); // RX, TX

void setup() {
  // Begin serial communication with Arduino and Arduino IDE (Serial Monitor)
  Serial.begin(9600);
  
  // Begin serial communication with SIM900A and set baud rate
  SIM900A.begin(9600);
  
  // Check if SIM900A is working
  Serial.println("Setting up SIM900A...");
  delay(1000); // Give time for module to stabilize
  SIM900A.println("AT"); // Send AT command to SIM900A
}

void loop() {
  // Forward every message from SIM900A to the Serial Monitor
  if (SIM900A.available()) {
    Serial.write(SIM900A.read());
  }
  // Forward every message from the Serial Monitor to SIM900A
  if (Serial.available()) {
    SIM900A.write(Serial.read());
  }
}

• Power Issues: If the SIM900A does not power up, check the power supply and connections.
• Signal Problems: Poor signal quality can affect communication. Ensure the antenna is properly connected and placed.
• SIM Card Not Recognized: Make sure the SIM card is inserted correctly and is activated.

• Power Supply: Use a power supply that can deliver a high transient current to avoid brown-out conditions.
• Baud Rate: Ensure the baud rate of the SIM900A matches the baud rate of the microcontroller's UART.
• AT Commands: Use AT commands to communicate with the SIM900A and check its status.

Q: What is the default baud rate of the SIM900A? A: The default baud rate is typically set to 9600 bps.

Q: Can I use the SIM900A for internet connectivity? A: Yes, the SIM900A supports GPRS for internet connectivity, but it is limited to 2G speeds.

Q: How can I reduce power consumption of the SIM900A? A: Utilize the power-down mode and control the sleep level via AT commands.

Q: What should I do if I can't communicate with the SIM900A? A: Double-check your wiring, ensure correct power supply, and verify that the SIM card is working and has credit.

This documentation provides a comprehensive guide to the SIM900A GSM/GPRS module, ensuring users can effectively integrate it into their projects. For further assistance, consult the SIM900A datasheet and application notes provided by the manufacturer.