SIM800L is a miniature cellular module which allows for GPRS transmission, sending and receiving SMS and making and receiving voice calls.

The SIM800L module allows your microcontroller (like Arduino, ESP32, etc.) to connect to a GSM cellular network to send/receive SMS, make/receive calls, or connect to the internet via GPRS. It's tiny in size, making it perfect for mobile or space-constrained applications.

Key Features

Ultra-compact and light weight
Supports SMS, voice, and GPRS data
Quad-band operation – usable worldwide
Low power consumption
Standard AT command set
Can be controlled by microcontrollers via UART

Pinout Overview

Pin	Function
VCC	3.7V – 4.4V input (NOT 5V!)
GND	Ground
TXD	Transmit (to RX of MCU)
RXD	Receive (to TX of MCU)
RST	Reset (active LOW)
NET	Network status LED pin

How to Use (with Arduino)

Wiring Example (with Level Shifter or Voltage Divider):

SIM800L VCC → 4.0V power supply
SIM800L GND → GND
SIM800L TX → Arduino RX (through voltage divider)
SIM800L RX ← Arduino TX (through voltage divider)
SIM800L RST → optional, use for manual reset

Basic AT Commands:

Typical Applications

IoT devices (remote monitoring, telemetry)
SMS alert systems
GSM-based home automation
Location tracking (when combined with GPS)
Voice call–based controls
Low-cost remote sensors.

Steps to Send an SMS Using SIM800L and Arduino

1. Required Components

SIM800L GSM Module (with antenna)
Microcontroller (e.g., Arduino UNO/Nano)
External power source (4.0V–4.2V, 2A capable)
Level shifter or voltage divider (for TX/RX safety)
Active SIM card (with SMS balance)

2. Wiring Connection (Example with Arduino UNO)

SIM800L Pin	Arduino Pin	Notes
VCC	4.0V (external)	Don’t connect to 5V — use a Li-ion battery or buck converter
GND	GND	Common ground with Arduino
TX	D7 (Software RX)	Connect via voltage divider (3.3V max input)
RX	D8 (Software TX)	Arduino TX should be lowered to 2.8–3.3V
RST	Optional	Pull LOW briefly to reset

3. Arduino Code to Send SMS

This code uses SoftwareSerial to communicate with SIM800L:

cpp

CopyEdit

#include <SoftwareSerial.h> SoftwareSerial sim800(7, 8); // RX, TX void setup() { sim800.begin(9600); Serial.begin(9600); delay(1000); Serial.println("Initializing..."); sim800.println("AT"); // Test AT delay(1000); sim800.println("AT+CMGF=1"); // Set SMS to text mode delay(1000); sim800.println("AT+CMGS=\"+1234567890\""); // Replace with recipient number delay(1000); sim800.print("Hello from Arduino via SIM800L!"); // Message body delay(500); sim800.write(26); // ASCII code of CTRL+Z to send SMS Serial.println("SMS Sent"); } void loop() { // Nothing to do here }

4. What You Should See

Your serial monitor will show "SMS Sent"
The recipient will receive your text
SIM800L must have good signal (check with AT+CSQ)
SIM must not have PIN lock and should be inserted properly

Troubleshooting Tips

Use a dedicated 4.2V 2A power source (SIM800L draws up to 2A when transmitting).
Make sure the baud rate matches (SIM800L usually uses 9600).
Wait for network registration: AT+CREG? should return 0,1
If SMS not sent, check SIM card status with AT+CPIN?

if you want to see how to do it you can watch this shot video can be helpful for you.

Smallest SIM800L GPRS GSM