Call And Message Using Arduino And Gsm Module | GSM Tutorial

Arduino + GSM Module: Make a Call and Send SMS

Imagine turning an Arduino and a GSM module (such as SIM900 or SIM800) into a miniature phone: you can dial out or send a message with the press of a button! Here's how to build your own simple project.

🔧 Components You’ll Need

Arduino Uno (or similar)

• Arduino Uno (or similar)

GSM module (SIM900, SIM800, SIM900A, etc.)

• GSM module (SIM900, SIM800, SIM900A, etc.)

Two pushbuttons

• Two pushbuttons

Two LEDs (with 220 Ω resistors)

• Two LEDs (with 220 Ω resistors)

Jumper wires and breadboard

• Jumper wires and breadboard

USB cable for uploading code

• USB cable for uploading code

A SIM card enabled for voice and SMS (2G network support)

• A SIM card enabled for voice and SMS (2G network support)

🧩 Circuit Setup

Follow these connections:

Arduino digital 10 → GSM TX

• Arduino digital 10 → GSM TX

Arduino digital 11 → GSM RX

• Arduino digital 11 → GSM RX

Arduino GND → GSM GND

• Arduino GND → GSM GND

Use Pushbutton 1 on Arduino D7 for calling

• Use Pushbutton 1 on Arduino D7 for calling

Use Pushbutton 2 on Arduino D8 for SMS

• Use Pushbutton 2 on Arduino D8 for SMS

LED 1 (on D5) lights during calling

• LED 1 (on D5) lights during calling

LED 2 (on D4) lights during SMS sending Power the GSM module with an appropriate supply (often 12 V/1 A or regulated 5 V/3–4 V depending on your module)

• LED 2 (on D4) lights during SMS sending Power the GSM module with an appropriate supply (often 12 V/1 A or regulated 5 V/3–4 V depending on your module)

📱 How It Works

Making a Call

Press Button 1 (D7)

• Press Button 1 (D7)

Arduino sends: ATD<phone_number>; to dial

• Arduino sends: ATD<phone_number>; to dial

LED 1 turns on while dialing

• LED 1 turns on while dialing

After a delay, Arduino sends ATH to hang up

• After a delay, Arduino sends ATH to hang up

Activity is echoed on the Serial Monitor

Activity is echoed on the Serial Monitor

Sending an SMS

Press Button 2 (D8)

• Press Button 2 (D8)

Arduino sends:

AT+CMGF=1 to enable text mode

• AT+CMGF=1 to enable text mode

AT+CMGS="phone number"

• AT+CMGS="phone number"

The message text

• The message text

Ctrl+Z (ASCII 26) to dispatch the SMS

• Ctrl+Z (ASCII 26) to dispatch the SMS
• Arduino sends:AT+CMGF=1 to enable text modeAT+CMGS="phone number"

The message textCtrl+Z (ASCII 26) to dispatch the SMS

LED 2 indicates the action is underway

• LED 2 indicates the action is underway

Confirmations appear on the Serial Monitor

• Confirmations appear on the Serial Monitor

Receiving SMS (Optional)

Arduino can also receive SMS using AT commands:

Use AT+CNMI=2,2,0,0,0 to configure forwarding

• Use AT+CNMI=2,2,0,0,0 to configure forwarding

Then monitor gsm.available() to read incoming SMS text and remote number

• Then monitor gsm.available() to read incoming SMS text and remote number
• Arduino can also receive SMS using AT commands:Use AT+CNMI=2,2,0,0,0 to configure forwardingThen monitor gsm.available() to read incoming SMS text and remote number

💻 Sample Code Snippet

cpp

CopyEdit

#include <SoftwareSerial.h>
SoftwareSerial gsm(10,11); // RX|TX

const int callBtn = 7, msgBtn = 8;
pinMode(callBtn, INPUT);
pinMode(msgBtn, INPUT);
pinMode(5, OUTPUT); // LED1
pinMode(4, OUTPUT); // LED2

void setup() {
delay(10000); // module startup
Serial.begin(9600);
gsm.begin(9600);
}
void loop() {
if (digitalRead(callBtn) == HIGH) {
gsm.println("ATD7007651787;"); // replace with your number
digitalWrite(5, HIGH);
delay(100);
gsm.println("ATH");
delay(2000);
digitalWrite(5, LOW);
Serial.println("Calling...");
}
if (digitalRead(msgBtn) == HIGH) {
gsm.println("AT+CMGF=1");
delay(1000);
gsm.println("AT+CMGS=\"7007651787\"\r");
delay(1000);
gsm.println("Hello from Arduino!");
delay(100);
gsm.write(26); // Ctrl+Z
Serial.println("Message sent");
digitalWrite(4, LOW);
}
if (gsm.available()) {
Serial.write(gsm.read());
}
}

cpp

CopyEdit
#include <SoftwareSerial.h>
SoftwareSerial gsm(10,11); // RX|TX

const int callBtn = 7, msgBtn = 8;
pinMode(callBtn, INPUT);
pinMode(msgBtn, INPUT);
pinMode(5, OUTPUT); // LED1
pinMode(4, OUTPUT); // LED2

void setup() {
  delay(10000);  // module startup
  Serial.begin(9600);
  gsm.begin(9600);
}
void loop() {
  if (digitalRead(callBtn) == HIGH) {
    gsm.println("ATD7007651787;");   // replace with your number
    digitalWrite(5, HIGH);
    delay(100);
    gsm.println("ATH");
    delay(2000);
    digitalWrite(5, LOW);
    Serial.println("Calling...");
  }
  if (digitalRead(msgBtn) == HIGH) {
    gsm.println("AT+CMGF=1");
    delay(1000);
    gsm.println("AT+CMGS=\"7007651787\"\r");
    delay(1000);
    gsm.println("Hello from Arduino!");
    delay(100);
    gsm.write(26);  // Ctrl+Z
    Serial.println("Message sent");
    digitalWrite(4, LOW);
  }
  if (gsm.available()) {
    Serial.write(gsm.read());
  }
}

⚠️ Important Tips & Troubleshooting

Ensure your SIM card supports the required 2G band in your country (e.g. many GSM modules only support 900 / 1800 MHz)

• Ensure your SIM card supports the required 2G band in your country (e.g. many GSM modules only support 900 / 1800 MHz)

Check power requirements: GSM modules often need steady current bursts of 1–2 A; using a separate regulator or battery is advised

• Check power requirements: GSM modules often need steady current bursts of 1–2 A; using a separate regulator or battery is advised

Proper logic level shifting may be necessary (Arduino 5 V → module 3.3 V pins) to avoid damaging the module

• Proper logic level shifting may be necessary (Arduino 5 V → module 3.3 V pins) to avoid damaging the module

Match baud rates between Arduino (Serial Monitor) and GSM module to avoid gibberish output

• Match baud rates between Arduino (Serial Monitor) and GSM module to avoid gibberish output