Six-LED Sequence and Traffic Lights

Build a six-LED chase, then arrange the same six outputs as two traffic lights. The traffic-light practical ends after the working sequence, with no end test.

Lesson 3 · Build a six-LED running sequence

Use six LEDs in a row. Each output pin has its own current-limiting resistor. Connect each LED cathode to GND. Check breadboard row connections before powering the circuit.

Six output channels

1LED 1: D2 → resistor → anode; cathode → GND

2LED 2: D3; LED 3: D4; LED 4: D5

3LED 5: D6; LED 6: D7 — same resistor and GND pattern

Six separate output circuits, viewed left to right

D2→ resistor →●→ GND

D3→ resistor →●→ GND

D4→ resistor →●→ GND

D5→ resistor →●→ GND

D6→ resistor →●→ GND

D7→ resistor →●→ GND

PHOTO TO ADDWide view of six LEDs in a straight row, all resistors visible.

void setup() {
  pinMode(2, OUTPUT); pinMode(3, OUTPUT);
  pinMode(4, OUTPUT); pinMode(5, OUTPUT);
  pinMode(6, OUTPUT); pinMode(7, OUTPUT);
}
void loop() {
  digitalWrite(2, HIGH); delay(200); digitalWrite(2, LOW);
  digitalWrite(3, HIGH); delay(200); digitalWrite(3, LOW);
  digitalWrite(4, HIGH); delay(200); digitalWrite(4, LOW);
  digitalWrite(5, HIGH); delay(200); digitalWrite(5, LOW);
  digitalWrite(6, HIGH); delay(200); digitalWrite(6, LOW);
  digitalWrite(7, HIGH); delay(200); digitalWrite(7, LOW);
}

The repeated lines are intentional: each LED is switched on, held briefly, then switched off before the next one lights.

Lesson 4 · Rearrange them as two traffic lights

Two groups of three

1Direction A: red D2, amber D3, green D4

2Direction B: red D5, amber D6, green D7

3Each pin → its own resistor → LED anode; all cathodes → GND

Traffic-light grouping (pin → resistor → LED → GND)

Direction A

🔴 Red D2

🟡 Amber D3

🟢 Green D4

Direction B

🔴 Red D5

🟡 Amber D6

🟢 Green D7

PHOTO TO ADDTwo clearly labelled red–amber–green stacks on the breadboard.

The diagram shows electrical connections. Arrange the physical LEDs as two separate vertical stacks so the two directions are easy to read.

const int ar=2, aa=3, ag=4;
const int br=5, ba=6, bg=7;
void setup() {
  pinMode(ar,OUTPUT); pinMode(aa,OUTPUT); pinMode(ag,OUTPUT);
  pinMode(br,OUTPUT); pinMode(ba,OUTPUT); pinMode(bg,OUTPUT);
  digitalWrite(ar,HIGH); digitalWrite(br,HIGH);
}
void loop() {
  // A: red+amber, then green. B stays red.
  digitalWrite(aa,HIGH); delay(1000);
  digitalWrite(ar,LOW); digitalWrite(aa,LOW);
  digitalWrite(ag,HIGH); delay(3000);
  digitalWrite(ag,LOW); digitalWrite(aa,HIGH); delay(1000);
  digitalWrite(aa,LOW); digitalWrite(ar,HIGH); delay(1000);

  // B: red+amber, then green. A stays red.
  digitalWrite(ba,HIGH); delay(1000);
  digitalWrite(br,LOW); digitalWrite(ba,LOW);
  digitalWrite(bg,HIGH); delay(3000);
  digitalWrite(bg,LOW); digitalWrite(ba,HIGH); delay(1000);
  digitalWrite(ba,LOW); digitalWrite(br,HIGH); delay(1000);
}

VIDEO TO ADDRecord the six-LED chase, rearrangement into two light stacks, and one complete cycle.