Hey folks, how are you? today I want to show you how to control more LED’s using less pins of Arduino. The name of the technique is Charlieplexing, it drives the pins of Arduino to be inputs or high state (in case of Arduino, only to inputs, since ATMEGA328 with Arduino does not allow high state).

We will learn how to implement charlieplexing with Arduino.

An example of it working is seen in the gif below, eight LED’s are drive by four Arduino pins.

The complete circuit is seen below.

The complete code for this example is seen below; note that at times some pins are set as inputs, this is part of the technique. All files show here are in this Github repository (including the schematics).

void setup() {
  // set the digital pin as output:
  pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);
  pinMode(4, OUTPUT);
  pinMode(5, OUTPUT);
}

void loop() {

    led1();
    delay(62);
    led5();
    delay(62);
    led2();
    delay(62);
    led6();
    delay(62);
    led3();
    delay(62);
    led7();
    delay(62);
    led4();
    delay(62);
    led8();
    delay(62);
  
}

void led1(){
  pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);
  pinMode(4, INPUT);
  pinMode(5, INPUT);
  digitalWrite(3, LOW);
  digitalWrite(2, HIGH);  
}
void led2(){
  pinMode(4, OUTPUT);
  pinMode(3, OUTPUT);
  pinMode(2, INPUT);
  pinMode(5, INPUT);
  digitalWrite(4, LOW);
  digitalWrite(3, HIGH);  
}
void led3(){
  pinMode(4, OUTPUT);
  pinMode(5, OUTPUT);
  pinMode(2, INPUT);
  pinMode(3, INPUT);
  digitalWrite(5, LOW);
  digitalWrite(4, HIGH);  
}
void led4(){
  pinMode(4, OUTPUT);
  pinMode(2, OUTPUT);
  pinMode(3, INPUT);
  pinMode(5, INPUT);
  digitalWrite(2, LOW);
  digitalWrite(4, HIGH);  
}
void led5(){
  pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);
  pinMode(4, INPUT);
  pinMode(5, INPUT);
  digitalWrite(2, LOW);
  digitalWrite(3, HIGH);  
}
void led6(){
  pinMode(4, OUTPUT);
  pinMode(3, OUTPUT);
  pinMode(2, INPUT);
  pinMode(5, INPUT);
  digitalWrite(3, LOW);
  digitalWrite(4, HIGH);  
}
void led7(){
  pinMode(4, OUTPUT);
  pinMode(5, OUTPUT);
  pinMode(2, INPUT);
  pinMode(3, INPUT);
  digitalWrite(4, LOW);
  digitalWrite(5, HIGH);  
}
void led8(){
  pinMode(4, OUTPUT);
  pinMode(2, OUTPUT);
  pinMode(3, INPUT);
  pinMode(5, INPUT);
  digitalWrite(4, LOW);
  digitalWrite(2, HIGH);  
}

Wanna see how to use digital input and outputs of Arduino? see here.