/**************************************/
/* Charlieplexing 6 LEDs with 3 Pins  */
/*                                    */
/* Code written by William Hart, 2011 */
/* http://williamhart.info        */
/*                                    */
/* Uses 3 pins to power a network of  */
/* 6 LEDs using the charlieplexing    */
/* technique.                         */ 
/**************************************/

#define LED_A 1
#define LED_B 2
#define LED_C 3
#define LED_D 4
#define LED_E 5

void setup()
{
  // first set all pins to input, or high impedance
  // (not strictly necessary as all pins are inputs by default)
  pinMode(LED_A, INPUT);
  pinMode(LED_B, INPUT);
  pinMode(LED_C, INPUT);
  pinMode(LED_D, INPUT);
  pinMode(LED_E, INPUT);
}

void loop()
{
  // run through a sample loop, lighting each LED

  // in turn and holding for half a second.

  set_pins(LED_B, LED_A);
  delay(10);
  set_pins(LED_A, LED_B);
  delay(10);
  set_pins(LED_A, LED_C);
  delay(10);
  set_pins(LED_A, LED_D);
  delay(10);
  set_pins(LED_A, LED_E);
  delay(10);
  
  set_pins(LED_C, LED_A);
  delay(10);
  set_pins(LED_C, LED_B);
  delay(10);
  set_pins(LED_B, LED_C);
  delay(10);
  set_pins(LED_B, LED_D);
  delay(10);
  set_pins(LED_B, LED_E);
  delay(10);

  set_pins(LED_D, LED_A);
  delay(10);
  set_pins(LED_D, LED_B);
  delay(10);
  set_pins(LED_D, LED_C);
  delay(10);
  set_pins(LED_C, LED_D);
  delay(10);
  set_pins(LED_C, LED_E);
  delay(10);

  set_pins(LED_E, LED_A);
  delay(10);
  set_pins(LED_E, LED_B);
  delay(10);
  set_pins(LED_E, LED_C);
  delay(10);
  set_pins(LED_E, LED_D);
  delay(10);
  set_pins(LED_D, LED_E);
  delay(10);
}

void set_pins(int high_pin, int low_pin)
{
  // reset all the pins
  reset_pins();

  // set the high and low pins to output
  pinMode(high_pin, OUTPUT);
  pinMode(low_pin, OUTPUT);

  // set high pin to logic high, low to logic low
  digitalWrite(high_pin, HIGH);
  digitalWrite(low_pin,LOW);
}

void reset_pins()
{
  // start by ensuring all pins are at input and low
  pinMode(LED_A, INPUT); 
  pinMode(LED_B, INPUT);
  pinMode(LED_C, INPUT);
  pinMode(LED_D, INPUT);
  pinMode(LED_E, INPUT);

  digitalWrite(LED_A, LOW);
  digitalWrite(LED_B, LOW);
  digitalWrite(LED_C, LOW);
  digitalWrite(LED_D, LOW);
  digitalWrite(LED_E, LOW);
}