Collision Warning System

1// Collision Warning System with Distance Sensor (HC-SR04)
2// Author: Ana Rodrigues
3// Oct 2, 2025
4// Object is farther than 50cm: Green LED lights up
5// Object is closer than 50 cm, but more than 10cm away: Yellow LED lights, buzzer plays 300Hz tone
6// Object is closer than 10cm: Red LED lights up, buzzer plays 500Hz tone
7
8//LED pins
9const int greenLED = 2;
10const int yellowLED = 3;
11const int redLED = 4;
12
13// Ultrasonic sensor pins
14const int trigPin = 9;
15const int echoPin = 10;
16
17// Passive buzzer pin
18const int buzzer = 11;
19
20void setup() {
21  pinMode(greenLED, OUTPUT);
22  pinMode(yellowLED, OUTPUT);
23  pinMode(redLED, OUTPUT);
24  pinMode(trigPin, OUTPUT);
25  pinMode(echoPin, INPUT);
26  Serial.begin(9600);
27}
28
29void loop() {
30  // Measure distance
31  digitalWrite(trigPin, LOW);
32  delayMicroseconds(2);
33  digitalWrite(trigPin, HIGH);
34  delayMicroseconds(10);
35  digitalWrite(trigPin, LOW);
36
37  long duration = pulseIn(echoPin, HIGH);
38  long distance = duration * 0.034 / 2;
39
40  Serial.print("Distance: ");
41  Serial.print(distance);
42  Serial.println(" cm");
43  
44  //Error in measurement:
45  if (distance <= 0)
46    return;
47
48  //Too close:
49  if (distance <= 10) {
50    digitalWrite(greenLED, LOW);
51    digitalWrite(yellowLED, LOW);
52    digitalWrite(redLED, HIGH);
53    tone(buzzer, 500); // Play 500Hz tone
54    return;
55  }
56
57  //Midrange:
58  if (distance <= 30) {
59    digitalWrite(greenLED, LOW);
60    digitalWrite(yellowLED, HIGH);
61    digitalWrite(redLED, LOW);
62    tone(buzzer, 300); // Play 300Hz tone
63    return;
64  }
65
66  //Normal status:
67  digitalWrite(greenLED, HIGH);
68  digitalWrite(yellowLED, LOW);
69  digitalWrite(redLED, LOW);
70  noTone(buzzer); // stop buzzer
71
72  delay(100);
73}