To detect when a car is in a parking lot, there are some sensors available; in this case, we will use a presence sensor like this:

In some parking lots, there is a gate that goes up when the driver arrives in front of it and they press the button and receive their ticket; in others, they have an identity card. Here is a common parking lot:

This is a prototype of the entrance to the parking lot:

Now we will make a sketch that we can use with Arduino; it detects when the car gets close to the sensor. We use the digitalread() instruction to detect a digital signal; this sensor activates with a signal in low, as shown in the following code:

    #include <Wire.h> 
    #include <LiquidCrystal_I2C.h>

    LiquidCrystal_I2C lcd(0x3F,16,2); // set the LCD address to 0x20 for a 16 chars and 2 line display

    //variables

    int cont = 0;
    int reading;

    void setup()
    {
      Serial.begin(9600);
      lcd.init();
      pinMode(13,OUTPUT);
      pinMode(2,INPUT_PULLUP);
    
      // Print a message to the LCD.
      lcd.backlight();
      lcd.print("Counting Cars");
      lcd.setCursor(0,1);
      lcd.print("Counting = 0 ");
     }

    void loop()
    {
      lectura = digitalRead(2);
      if (reading == LOW){
        digitalWrite(13,HIGH);
        delay(1000);
        digitalWrite(13,LOW);
        cont = cont + 1;
        lcd.setCursor(0,1);
        lcd.print("Counting = ");
        lcd.print(cont);
        Serial.print("Counting = ");
        Serial.println(cont);

      // this condition counts until 21 cars after that the count returns to zero
        if (cont == 21){
          cont = 0;
          lcd.setCursor(0,1);
          lcd.print(" ");
          lcd.setCursor(0,1);
          lcd.print("Counting = ");
          lcd.print(cont);
          Serial.print("Counting = ");
          Serial.println(cont);
        }
      }
    }

The final connections look like this:

This information of the total number can be displayed on a big screen or we implement storing the number of cars or spaces in a database; we will discuss this in the following sections.