binary-lights.md

This code will flag binary numbers up to 15 using the 4 LEDS connected to pins 10-13.

I wrote (vibe coded) this for my niece as she learns how to program an Arduino.

// We are using 4 LEDs connected to pins 10, 11, 12, and 13
// These 4 LEDs will show numbers in binary (from 0 to 15)

// This is an array.
// An array is a list of values stored under one name.
// Instead of writing four separate variables for four pins,
// we store them all in one list called "pins".
int pins[4] = {10, 11, 12, 13};
// pins[0] = 10
// pins[1] = 11
// pins[2] = 12
// pins[3] = 13

void setup() {
  // setup() runs once when the Arduino turns on

  // This loop goes through the array one item at a time
  for (int i = 0; i < 4; i++) {

    // Set each pin in the array to OUTPUT mode
    // OUTPUT means the Arduino can turn the LED on or off
    pinMode(pins[i], OUTPUT);

    // Make sure the LED starts turned off
    digitalWrite(pins[i], LOW);
  }
}

void loop() {
  // loop() runs over and over forever

  // Count from 0 to 15
  // 0–15 fits in 4 binary digits (0000 to 1111)
  for (int number = 0; number < 16; number++) {

    // Each LED represents one binary digit (bit)

    // Bit 0 (1's place) → pin 10
    if (number & 1) digitalWrite(pins[0], HIGH);
    else            digitalWrite(pins[0], LOW);

    // Bit 1 (2's place) → pin 11
    if (number & 2) digitalWrite(pins[1], HIGH);
    else            digitalWrite(pins[1], LOW);

    // Bit 2 (4's place) → pin 12
    if (number & 4) digitalWrite(pins[2], HIGH);
    else            digitalWrite(pins[2], LOW);

    // Bit 3 (8's place) → pin 13
    if (number & 8) digitalWrite(pins[3], HIGH);
    else            digitalWrite(pins[3], LOW);

    // Wait half a second so we can see the LEDs change
    delay(500);
  }
}