Multiple Outputs: A Traffic Signal

01

What you will build

Three individually driven LEDs on D8, D9 and D10 in a traffic-light-like sequence.

Why it matters

Repetition in wiring and code motivates loops and arrays after a working simple build.

What you will learn

• multiple independent output pins
• state progression and timing
• repetition, loops and arrays as optional improvements

02

Parts per station

• 1 each Arduino Uno R3An independently programmable Uno R3 per simultaneous station.
• 1 each 830-point solderless breadboardA small breadboard is a possible substitute after inspection.
• 3 each Assorted LEDsOrdinary discrete LEDs; colors are optional.
• 3 each Resistor assortmentOne verified 220–330 Ω current-limiting resistor per LED; count and values before class.
• several assorted Jumper wire assortmentCount leads usable for the chosen circuit before class.
• 1 each 10-foot USB-A to USB-B cableAvailability unconfirmed. One working USB-A to USB-B DATA cable for upload; cable length need not be 10 feet. This canonical item is procurement-only, so existing cable stock must be verified, not assumed.

03

Assembly

1. 01

   Disconnect USB; copy the Lab 2 circuit three times, one series resistor per LED.

2. 02

   Connect LED 1 to D8, LED 2 to D9 and LED 3 to D10; connect all cathodes to Uno GND.

3. 03

   Check rows, polarity and three resistors; reconnect, verify and upload the core sketch.

4. 04

   Name each visible phase aloud; change one phase delay only.

Predict before you run

• Which LED comes after D8, and for how long?
• What happens if two phases are given the same HIGH state?

04

Code

After the first LED turns off, the second phase lights D9.

// Labels are roles; actual LED colors may differ.
const int redLed = 8;
const int amberLed = 9;
const int greenLed = 10;

void setup() {
  pinMode(redLed, OUTPUT);
  pinMode(amberLed, OUTPUT);
  pinMode(greenLed, OUTPUT);
}

void loop() {
  digitalWrite(redLed, HIGH);
  digitalWrite(amberLed, LOW);
  digitalWrite(greenLed, LOW);
  delay(1000);
  digitalWrite(redLed, LOW);
  digitalWrite(amberLed, HIGH);
  delay(500);
  digitalWrite(amberLed, LOW);
  digitalWrite(greenLed, HIGH);
  delay(1000);
  digitalWrite(greenLed, LOW);
}

How it works

Repetition in wiring and code motivates loops and arrays after a working simple build.

Repeated physical outputs have repeated setup and control logic; abstraction becomes useful as output count grows.

Experiments & challenges

• Change only the middle phase duration.
• Swap the positions of two LEDs with USB disconnected, then predict which physical position lights first.

Check your understanding

Troubleshooting