This is the kit I purchased.

This is the code I'm using for 8 LEDs
*/
int timer = 400; // The higher the number, the slower the timing.
int ledPins[] = {
6, 7, 8, 9, 10, 11, 12, 13 }; // an array of pin numbers to which LEDs are attached
int pinCount = 8; // the number of pins (i.e. the length of the array)
void setup() {
// the array elements are numbered from 0 to (pinCount - 1).
// use a for loop to initialize each pin as an output:
for (int thisPin = 0; thisPin < pinCount; thisPin++) {
pinMode(ledPins[thisPin], OUTPUT);
}
}
void loop() {
// loop from the lowest pin to the highest:
for (int thisPin = 0; thisPin < pinCount; thisPin++) {
// turn the pin on:
digitalWrite(ledPins[thisPin], HIGH);
delay(timer);
// turn the pin off:
digitalWrite(ledPins[thisPin], LOW);
}
// loop from the highest pin to the lowest:
for (int thisPin = pinCount - 1; thisPin >= 0; thisPin--) {
// turn the pin on:
digitalWrite(ledPins[thisPin], HIGH);
delay(timer);
// turn the pin off:
digitalWrite(ledPins[thisPin], LOW);
}
}
This the code I'm trying to use for 12 LEDs
*/
int timer = 400; // The higher the number, the slower the timing.
int ledPins[] = {
2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 }; // an array of pin numbers to which LEDs are attached
int pinCount = 12; // the number of pins (i.e. the length of the array)
void setup() {
// the array elements are numbered from 0 to (pinCount - 1).
// use a for loop to initialize each pin as an output:
for (int thisPin = 0; thisPin < pinCount; thisPin++) {
pinMode(ledPins[thisPin], OUTPUT);
}
}
void loop() {
// loop from the lowest pin to the highest:
for (int thisPin = 0; thisPin < pinCount; thisPin++) {
// turn the pin on:
digitalWrite(ledPins[thisPin], HIGH);
delay(timer);
// turn the pin off:
digitalWrite(ledPins[thisPin], LOW);
}
// loop from the highest pin to the lowest:
for (int thisPin = pinCount - 1; thisPin >= 0; thisPin--) {
// turn the pin on:
digitalWrite(ledPins[thisPin], HIGH);
delay(timer);
// turn the pin off:
digitalWrite(ledPins[thisPin], LOW);
}
}
The only thing that is changed is the pinCount and number of outputs.