For Loop Iteration (aka The Knight Rider)

Often you want to iterate over a series of pins and do something to each one. For instance, this example blinks 6 LEDs attached to the Arduino or Genuino by using a for() loop to cycle back and forth through digital pins 2-7. The LEDS are turned on and off, in sequence, by using both the digitalWrite() and delay() functions .

We also call this example "Knight Rider" in memory of a TV-series from the 80's where David Hasselhoff had an AI machine named KITT driving his Pontiac. The car had been augmented with plenty of LEDs in all possible sizes performing flashy effects. In particular, it had a display that scanned back and forth across a line, as shown in this exciting fight between KITT and KARR. This example duplicates the KITT display.

Hardware Required

  • Arduino or Genuino Board
  • 6 220 ohm resistors
  • 6 LEDs
  • hook-up wires
  • breadboard


Connect six LEDS, with 220 ohm resistors in series, to digital pins 2-7 on your Arduino.

click the image to enlarge

image developed using Fritzing. For more circuit examples, see the Fritzing project page


click the image to enlarge


The code below begins by utilizing a for() loop to assign digital pins 2-7 as outputs for the 6 LEDs used.

In the main loop of the code, two for() loops are used to loop incrementally, stepping through the LEDs, one by one, from pin 2 to pin seven. Once pin 7 is lit, the process reverses, stepping back down through each LED.

  For Loop Iteration

 Demonstrates the use of a for() loop.
 Lights multiple LEDs in sequence, then in reverse.

 The circuit:
 * LEDs from pins 2 through 7 to ground

 created 2006
 by David A. Mellis
 modified 30 Aug 2011
 by Tom Igoe

This example code is in the public domain.

int timer = 100;           // The higher the number, the slower the timing.

void setup() {
  // use a for loop to initialize each pin as an output:
  for (int thisPin = 2; thisPin < 8; thisPin++) {
    pinMode(thisPin, OUTPUT);

void loop() {
  // loop from the lowest pin to the highest:
  for (int thisPin = 2; thisPin < 8; thisPin++) {
    // turn the pin on:
    digitalWrite(thisPin, HIGH);
    // turn the pin off:
    digitalWrite(thisPin, LOW);

  // loop from the highest pin to the lowest:
  for (int thisPin = 7; thisPin >= 2; thisPin--) {
    // turn the pin on:
    digitalWrite(thisPin, HIGH);
    // turn the pin off:
    digitalWrite(thisPin, LOW);

See Also:

  • for()
  • digitalWrite()
  • delay()

  • Arrays - A variation on the For Loop iteration example that demonstrates how to use an array.
  • IfStatementConditional - Use an ‘if statement’ to change the output conditions based on changing the input conditions.
  • switchCase - How to choose between a discrete number of values.
  • switchCase2 - A second switch-case example, showing how to take different actions based on the characters received in the serial port.
  • WhileStatementConditional - How to use a while loop to calibrate a sensor while a button is being read.

Last revision 2015/07/29 by SM