4. Traffic Light

This lesson uses: Arduino UNO R3 board, TinkerBlock TK03 Traffic Light module, jumper wires (or breadboard). Control three LEDs in sequence; learn multi-pin digital output and #define. Outcome: red on 5 s → green on 5 s → yellow on 2 s, then repeat.

1. Wiring

Connect TK03 Traffic Light to Arduino (three LEDs to D2, D3, D4; in code use 2, 3, 4 for these pins):

• GND → Arduino GND
• RED → Arduino D2
• YELLOW → Arduino D3
• GREEN → Arduino D4
• NC — leave unconnected

2. New sketch

1. Arduino IDE: File → New (or Ctrl/Cmd + N) to create a blank sketch
2. Confirm board and port are selected (same as Lesson 01)
3. Type the code below into the default setup() and loop() yourself

3. Program structure

Same as last lesson: two fixed blocks setup() and loop().

• setup(): Tell the board “pins 2, 3, 4 are for the LEDs”; runs once.
• loop(): Keep repeating “red on 5 s → green on 5 s → yellow on 2 s → back to red”.

Type the code below and the red, green, and yellow LEDs will take turns like a traffic light.

4. Code to write

Type the code below line by line into setup() and loop() (do not copy-paste; typing it yourself helps you remember):

// Traffic light: red(D2), yellow(D3), green(D4) on in sequence, others off
#define RED_PIN 2      // red to D2
#define YELLOW_PIN 3   // yellow to D3
#define GREEN_PIN 4    // green to D4

void setup() {
  pinMode(RED_PIN, OUTPUT);     // red / yellow / green all outputs
  pinMode(YELLOW_PIN, OUTPUT);
  pinMode(GREEN_PIN, OUTPUT);
}

void loop() {
  // Red on 5 s, yellow and green off
  digitalWrite(RED_PIN, HIGH);
  digitalWrite(YELLOW_PIN, LOW);
  digitalWrite(GREEN_PIN, LOW);
  delay(5000);

  // Green on 5 s, red and yellow off
  digitalWrite(RED_PIN, LOW);
  digitalWrite(YELLOW_PIN, LOW);
  digitalWrite(GREEN_PIN, HIGH);
  delay(5000);

  // Yellow on 2 s, red and green off
  digitalWrite(RED_PIN, LOW);
  digitalWrite(YELLOW_PIN, HIGH);
  digitalWrite(GREEN_PIN, LOW);
  delay(2000);
}

Program notes

Overall idea: Three pins for three LEDs; in loop() follow the order red → green → yellow, only one HIGH at a time and the others LOW, then delay to hold each phase. Use #define to name the pin numbers so you only change one place when wiring changes and the code is easier to read.

5. Hands-on

1. After entering the code, click Verify (✓) to compile
2. Click Upload (→) to upload to the board
3. Watch TK03 Traffic Light: red 5 s → green 5 s → yellow 2 s, then repeat
4. Change delay(5000) to delay(2000) and upload again; observe the change

Expected result:

Proceed to Lesson 05.

6. Common issues

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