Binary Counter on LEDs

Part of the Outputs section of Coddy's Arduino journey. Lesson 19 of 24.

Four LEDs can show any number from 0 to 15 in binary, the way computers store numbers. Each LED is a place worth twice the one before it: 1, 2, 4 and 8. A lit LED adds its value:

5 is 4 + 1: the LEDs worth 4 and 1 are lit
10 is 8 + 2
15 is all four

Each place is called a bit, numbered from 0, the one worth 1. bitRead(number, n) gives bit n of a number, 1 or 0:

bitRead(5, 0);  // 1: 5 has the 1
bitRead(5, 1);  // 0: 5 has no 2
bitRead(5, 2);  // 1: 5 has the 4

Since 1 is HIGH and 0 is LOW, bit i can go straight to LED i:

for (int i = 0; i < 4; i++) {
  digitalWrite(ledPins[i], bitRead(count, i));
}

Here ledPins[0], pin 2, is the LED on the right, worth 1, like the last digit of a number.

Challenge

Medium

Make the four LEDs count in binary:

start count at 0
show it on the LEDs with bitRead(), bit i on ledPins[i]
wait 250 ms, add 1, and after 15 start again at 0

Press Run, then Check.

Try it yourself

int ledPins[] = {2, 3, 4, 5};  // worth 1, 2, 4, 8
int count = 0;

void setup() {
  for (int i = 0; i < 4; i++) {
    pinMode(ledPins[i], OUTPUT);
  }
}

void loop() {
  // show count in binary, wait 250 ms, then count up (back to 0 after 15)
}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Outputs

Practice on your own: Arduino playground