Notes

const int trig = 12; // This command labels the trig pin on the sensor to pin 12 on the arduino board
const int echo = 13; // This command labels the echo pin on the sensor to pin 13 on the arduino board

const int redLED = 6; // This command labels red led to pin number 6 on the arduino board
const int yellowLED = 10; // This command labels the yellow led to pin number 10 on the arduino board
const int greenLED = 11; // This command labels the green led to pin number 11 on the arduino boarc

int duration = 0; // This command sets the duration to 0
int distance = 0; // This command sets the distance to 0

void setup() // This command only runs once in the program to setup the code
{
Serial.begin(9600); // This command sets the baud rate of the arduino to 9600
pinMode(trig , OUTPUT); // This command sets the trig pin as an output
pinMode(echo , INPUT); // This command sets the echo pin on the sensor as an input

pinMode(yellowLED , OUTPUT); // This command sets the yellow led as an output
pinMode(redLED , OUTPUT); // This command sets the red led as an output
pinMode(greenLED , OUTPUT); // This command sets the green led as an output



}

void loop() // This command is the main body of the program, the code written inside loops indefinitely
{
digitalWrite(trig , HIGH); // This command sets the trigger pin to high
delayMicroseconds(1000); // This command pauses the code by 1000 microseconds
digitalWrite(trig , LOW); // This command sets the trigger pin to low
// These three codes sends an ultrasonic pulse from the sensor
duration = pulseIn(echo , HIGH); // This command is used to measure the duration of the echo pulse
distance = (duration/2) / 28.5 ; // This command divides the duration by 2 and then divides by the speed of sound in the air (28.5cm/ms) to calculate the distance to the object
Serial.println(distance); // This command then displays the distance value to the serial monitor

if ( distance <= 10) // This command checks whether the distance is less than or equal to 10
{
digitalWrite(redLED, HIGH); // This command switches on the red led
}
else // This command is activated when the condition for the if command has not been achieved
{
digitalWrite(redLED, LOW); // This command switches off the red led
}
if ( distance >= 10 && distance <= 25) // This command checks whether the distance is more than or equal to 10 and less than or equal to 25
{
digitalWrite(yellowLED, HIGH); // This command switches the yellow led on
}
else // This command activates when the if command condition has not been acheived
{
digitalWrite(yellowLED, LOW); // This command switches the yellow led off
}
if ( distance >= 25 ) // This command checks whether the distance from the sensor is more than or equal to 25
{
digitalWrite(greenLED, HIGH); // This command switches the green led on
}
else // This command activates when the if command condition has not been achieved
{
digitalWrite(greenLED, LOW); // This command switches the green led off
}}