How to Connect Arduino Uno with SIM800L and Fix Network Connection Issues

Introduction

The SIM800L module is a popular GSM/GPRS module used for IoT projects, SMS, and call functionalities. However, many users face issues where the module blinks every second, connects to the network briefly, and then disconnects. This happens because the SIM800L requires a power boost during network registration. In this guide, I’ll show you how to properly connect the SIM800L to an Arduino Uno and fix the power instability issue using a capacitor.

Components Required

• Arduino Uno

• SIM800L GSM Module

• 1000µF 16V Capacitor (Electrolytic)

• 2A Power Supply (or a good-quality 5V/2A adapter)

• Jumper Wires

• Breadboard (optional)

Wiring the SIM800L to Arduino Uno

The SIM800L operates at 3.7V-4.2V, but its peak current can reach up to 2A during transmission. The Arduino’s 5V pin cannot supply this much current, so we need an external power source.

Connections:

1. SIM800L VCC → External 4V Power Supply (or 5V with a voltage regulator)

2. SIM800L GND → Common Ground with Arduino & Power Supply

3. SIM800L RX → Arduino TX (Pin 10 via SoftwareSerial)

4. SIM800L TX → Arduino RX (Pin 11 via SoftwareSerial)

Note: Always use a voltage regulator (like LM2596) if supplying 5V to avoid damaging the SIM800L.

The Power Stability Fix

Many users report that the SIM800L blinks every second, connects, then disconnects. This happens because the module requires a sudden current surge when registering to the network, and the power supply cannot provide it.

Solution: Add a 1000µF 16V Capacitor

• Connect the positive leg of the capacitor to the VCC of the SIM800L.

• Connect the negative leg to the GND of the SIM800L.

This capacitor acts as a power reservoir, supplying the extra current needed during network registration.

Arduino Code Example

Here’s a basic code to test the SIM800L connection:

#include <SoftwareSerial.h>

SoftwareSerial sim800l(10, 11); // RX, TX (Arduino pins)

void setup() {
  Serial.begin(9600);
  sim800l.begin(9600);
  delay(1000);

  Serial.println("Initializing SIM800L...");
  sim800l.println("AT"); // Test communication
  delay(500);
}

void loop() {
  // Read responses from SIM800L and print to Serial Monitor
  if (sim800l.available()) {
    Serial.write(sim800l.read());
  }

  // Send AT commands from Serial Monitor to SIM800L
  if (Serial.available()) {
    sim800l.write(Serial.read());
  }
}

Testing the Connection

1. Upload the code to Arduino.

2. Open the Serial Monitor (9600 baud).

3. If the module responds with OK and +CREG: 0,1 (registered to home network), it’s working correctly.

Troubleshooting

• No Response from SIM800L? Check wiring and baud rate.

• Still Disconnecting? Use a better power supply (2A recommended).

• SIM Card Not Detected? Ensure the SIM is properly inserted and unlocked.

Conclusion

By adding a 1000µF 16V capacitor between the VCC and GND of the SIM800L, you provide the necessary power boost for stable network connectivity. This simple fix resolves the common issue of frequent disconnections.

Try it out, and let me know in the comments if it worked for you! 🚀