Traffic light

Goal

We will simulate a traffic light which can be started using a button.

Materials

• Red LED
• Yellow LED
• Green LED
• 3x 470Ω resistor
• Button
• 10kΩ resistor

Setup Description

Hardware configuration

Software Sketch

int red = 13;
int yellow = 12;
int green = 11;

int button = 8;

void setup() {
  pinMode(red, OUTPUT);
  pinMode(yellow, OUTPUT);
  pinMode(green, OUTPUT);

  pinMode(button, INPUT);

  // set of traffic lights first to RED
  digitalWrite(red, HIGH);
  digitalWrite(yellow, LOW);
  digitalWrite(green, LOW);
}

void loop() {

  // Check if button is pressed
  if (digitalRead(button) == HIGH) {
    delay(5000);

    // RED to GREEN
    digitalWrite(red, HIGH);
    digitalWrite(yellow, HIGH);
    digitalWrite(green, LOW);

    delay(1000);

    digitalWrite(red, LOW);
    digitalWrite(yellow, LOW);
    digitalWrite(green, HIGH);

    delay(5000);

    // GREEN to RED
    digitalWrite(red, LOW);
    digitalWrite(yellow, HIGH);
    digitalWrite(green, LOW);

    delay (1000);

    digitalWrite(red, HIGH);
    digitalWrite(yellow, LOW);
    digitalWrite(green, LOW);
  }
}

• At the beginning of the loop() function we check to see if the start button is pressed.
• digitalRead(button) reads the current state of the button. If pressed, the function outputs HIGH, otherwise LOW.
• To check whether the button has been pressed, the digitalRead(button) must be compared with HIGH. The comparison is made with two equal signs == (comparative operator). A match = is an assignment, such as int red = 13.