This example fades 12 LEDs up and the down, one by one, on an Arduino Mega board.
Connect the longer, positive legs of (anodes) 12 LEDs to digital pins 2-13 through 220 ohm current limiting resistors. Connect the shorter, negative legs (cathodes) to ground.
setup() function of the code below, a
for() loop is used to assign digital pins 2-13 of the Mega as outputs.
Next, in the
loop() function of the program below, a trio of nested
for() loops are used.