GSM Car Ignition and Central Lock Circuit Using Arduino

In this post I will show how to construct a GSM based car security system using Arduino, which can lock and unlock car’s ignition system and central lock by sending a password SMS to car from your cellphone

Car theft can be a heart break; it feels like your loved one got kidnapped. It hurts more when an old car which you spend years with it got stolen. Old cars and low tier cars may get stolen often because they offer less security features.

As the time progress new methods are invented to exploit the cars, covering those exploits in mainstream and old cars can cost huge sum of money.

The proposed project can add another layer of security to your car at cheap cost, which might save your car from getting stolen one day.

The proposed project consist of GSM modem (SIM 800/900) which is the heart of the project, an Arduino board which acts as brain of the project.

Few relays interfaced with Arduino board enables and disabled the ignition and central lock of the car.

A valid SIM card with working SMS plan is required to operate this project and try to take advantage of the SMS offers availed by your network provider to reduce the expenses due to SMS.

Now let’s look at the circuit diagram of this cellphone controlled Arduino based GSM car central locking system:

The above circuit is fairly easy to replicate one. The GSM modem is interfaced with Arduino’s Tx and Rx pin.

The Tx of Arduino is connected to Rx of GSM modem and Rx of Arduino is connected Tx of GSM modem i.e. Tx to Rx and Rx to Tx.

Ground to ground connection between Arduino and GSM modem is also established.

A 9V regulator 7809 is added in the circuit to provide to fixed voltage to GSM modem and arduino board as the battery voltage is subjected to change while ignition and charging, higher than 12 volt may damage the boards.

The Arduino’s PIN # 7 is the output to the central lock and ignition lock mechanism.

Arduino Car Ignition lock diagram:

The diodes are connected to prevent high voltage spike from relay due to back EMF.

A fuse must be connected at the input as the short circuit can turn into catastrophic damage to the car.

A switch is provided which may be placed inside the bonnet. It can used to turn off the circuit if you are not planning to use the car for more than a week which will avoid battery drain.

NOTE: If the circuit is turned off (using switch) the central and ignition lock is activated and your car is safe.

Program:

//----------------Program developed by R.Girish------------//

int temp = 0;
int i = 0;
int j = 0;

char str[15];                 // Incoming SMS buffer
boolean state = false;

const int LOCK = 7;

void setup()
{
  Serial.begin(9600);

  pinMode(LOCK, OUTPUT);
  digitalWrite(LOCK, LOW);

  // GSM module warm-up delay
  for (j = 0; j < 60; j++)
  {
    delay(1000);
  }

  Serial.println("AT+CNMI=2,2,0,0,0");
  delay(1000);

  Serial.println("AT+CMGF=1");
  delay(500);

  Serial.println("AT+CMGS=\"+91xxxxxxxxxx\"\r"); // Replace x with mobile number
  delay(1000);

  Serial.println("Your car is ready to receive SMS commands.");
  delay(100);

  Serial.println((char)26);   // CTRL+Z
  delay(1000);
}

void loop()
{
  if (temp == 1)
  {
    check();

    temp = 0;
    i = 0;
    memset(str, 0, sizeof(str));   // Clear buffer

    delay(1000);
  }
}

void serialEvent()
{
  while (Serial.available())
  {
    if (Serial.find("/"))          // Start delimiter
    {
      delay(1000);

      while (Serial.available())
      {
        char inChar = Serial.read();

        if (i < (sizeof(str) - 1)) // Prevent overflow
        {
          str[i++] = inChar;
        }

        if (inChar == '/')
        {
          str[i - 1] = '\0';       // Proper string termination
          temp = 1;
          return;
        }
      }
    }
  }
}

void check()
{
  //--------------------------------------------------------------------------//
  if (!(strncmp(str, "qwerty", 6)))   // Password
  //--------------------------------------------------------------------------//
  {
    if (!state)
    {
      digitalWrite(LOCK, HIGH);
      delay(1000);

      Serial.println("AT+CMGS=\"+91xxxxxxxxxx\"\r");
      delay(1000);

      Serial.println("Central Lock: Unlocked.");
      Serial.println("Ignition Lock: Unlocked.");

      delay(100);
      Serial.println((char)26);

      state = true;
      delay(1000);
    }
    else
    {
      digitalWrite(LOCK, LOW);
      delay(1000);

      Serial.println("AT+CMGS=\"+91xxxxxxxxxx\"\r");
      delay(1000);

      Serial.println("Central Lock: Locked.");
      Serial.println("Ignition Lock: Locked.");

      delay(100);
      Serial.println((char)26);

      state = false;
      delay(1000);
    }
  }
  else if (!(strncmp(str, "status", 6)))
  {
    Serial.println("AT+CMGS=\"+91xxxxxxxxxx\"\r");
    delay(1000);

    Serial.println("The System is Working Fine.");

    if (!state)
    {
      Serial.println("Central Lock: Locked.");
      Serial.println("Ignition Lock: Locked.");
    }
    else
    {
      Serial.println("Central Lock: Unlocked.");
      Serial.println("Ignition Lock: Unlocked.");
    }

    delay(100);
    Serial.println((char)26);
    delay(1000);
  }
}

//----------------Program developed by R.Girish------------//

NOTE 1:

The user has to place the password in the code before uploading to Arduino.

//--------------------------------------------------------------------------//

if(!(strncmp(str,"qwerty",6))) // (Password Here, Length)

//--------------------------------------------------------------------------//

Replace the “qwerty” with your own password and change the number 6 to length of your password. For example:

if(!(strncmp(str,"@rduino",7))) // (Password Here, Lenght)

“@rduino” is the password and it has 7 letters (Length). You can place numbers, letters, special characters and combination of these. The password is case sensitive.

NOTE 2:

Replace all the “xxxxxxxxxxx” with car owner’s 10 digit phone number in the code at four places:

Serial.println("AT+CMGS=\"+91xxxxxxxxxx\"\r"); // Replace x with mobile number

How to operate this project with cellphone SMS:

• Sending /status/ to GSM modem will send an SMS to car owner’s phone number about the current status of the lock.

• Sending the correct password will toggle the state of the central and ignition lock.

Here is the screen shot:

The above result is from the tested prototype.

• Sending /status/ to the SIM card number inserted in GSM modem will send an acknowledgement SMS regarding the current status of the lock to car owner’s phone number.

• Sending the correct password to GSM modem in the above case /qwerty/ is the password, this will unlock the central and ignition lock. It will also send an acknowledgement SMS as shown above.

• Sending the same correct password again will lock the central and ignition lock.

NOTE 3: Start your password with “/” and also end with “/”

NOTE 4: Once the circuit is turned on please wait about a minute. The circuit will send an SMS saying “Your car is ready to accept SMS command” to car owner’s cellphone number. Only then you can send those SMS commands.

If you have any specific questions regarding this GSM car ignition lock, central lock circuit using Arduino, you can send them through the below given comment box