https://medium.com/jungletronics

_88_logicCounter_Extensible_4bits_03.ino

/* Project: Ardu_Series # 88
 *   Binary Counter - Logic Analyzer - Building an LED Binary Counter & Improving The Code
 *   
 *   INO file: _88_logicCounter_Extensible_4bits_03.ino
 *   
 *  Binary Counter.
 *
 *  Description: With 4xLEDs we can display binary numbers from 0 to 15;
                 This code consomes just 2326 bytes (3% of program storage space)
                 and Global variables use 26 bytes (1%) of dynamic memory:)
                 and beyond this, it has Extensibility!
                 Extensibility is a software engineering and systems design principle 
                 that provides for future growth. Extensibility is a measure of the 
                 ability to extend a system and the level of effort required to implement the extension.
 *
 *  Wiring involves:
 *
 * Output PIN XX -> LED -> 220k resister -> Ground
 *
 * Repeat that for each of the eight LEDs.
 *
 *  In my case I wired them on pins 1,2,3,4,5,6,7,8.
 *
 */

                        // The pins to which we've wired each of the LEDs
int ledPins[] = {1, 2, 3, 4};

                        // The number we're going to display.
byte count;

                        // The delay between each count
int waitTime=500;

/*
 * Set each pin to be used as output, and default to zero.
 */
void setup(void)
{
    for (byte i = 0; i < 4; i++) {
    pinMode(ledPins[i], OUTPUT);
    }
  count = 0;
}

/*
 *  Constantly increase, display, and delay.
 */
void loop(void)
{
  dispBinary(count++);
  delay(waitTime);
}

/*
 *  Show a single number.
 */
void dispBinary(byte n)
{
  for (byte i = 0; i < 4; i++) {   
    digitalWrite(ledPins[i], n & 1);
    n /= 2;
    } 
}