Analog Write with 12 LEDs on an Arduino
This example fades 12
LEDs up and the down, one by one, on an Arduino board.
Hardware Required
- Arduino Mega Board
- (12) LEDs
- (12) 220 ohm resistors
- hook up wire
- breadboard
Circuit
image developed using Fritzing. For more circuit examples, see the Fritzing project page
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.
Schematic
Code
In the
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.
The first of these loops,
for (int thisPin =lowestPin; thisPin <= highestPin; thisPin++)
moves through each of the LEDS one by one, from
the lowest pin to the highest. Before this loop is allowed to move from
one pin to the next, two things must be accomplished. First, you
brighten the individual LED through these
lines of code:
for (int brightness
= 0; brightness
< 255; brightness
++) {
analogWrite(thisPin
, brightness
);
delay(2);
}
With each pass through the loop above, the
variable brightness increases by one point, and that value is written
to the pin currently selected to the main loop. One that pin reaches the
maximum PWM value (255), the following loop kicks in:
for (int brightness = 255; brightness >= 0; brightness--) {
analogWrite(thisPin, brightness);
delay(2);
}
This loop subtracts a point from the brightness variable, dimming the LED back down to 0. Once zero is reached, the main
for() loop kicks in, and the program moves on to the next LED pin, repeating all the steps mentioned above.
/*
Mega analogWrite() test
This sketch fades LEDs up and down one at a time on digital pins 2 through 13.
This sketch was written for the Arduino Mega, and will not work on previous boards.
The circuit:
* LEDs attached from pins 2 through 13 to ground.
created 8 Feb 2009
by Tom Igoe
This example code is in the public domain.
*/
// These constants won't change. They're used to give names
// to the pins used:
const int lowestPin = 2;
const int highestPin = 13;
void setup() {
// set pins 2 through 13 as outputs:
for (int thisPin =lowestPin; thisPin <= highestPin; thisPin++) {
pinMode(thisPin, OUTPUT);
}
}
void loop() {
// iterate over the pins:
for (int thisPin =lowestPin; thisPin <= highestPin; thisPin++) {
// fade the LED on thisPin from off to brightest:
for (int brightness = 0; brightness < 255; brightness++) {
analogWrite(thisPin, brightness);
delay(2);
}
// fade the LED on thisPin from brithstest to off:
for (int brightness = 255; brightness >= 0; brightness--) {
analogWrite(thisPin, brightness);
delay(2);
}
// pause between LEDs:
delay(100);
}
}
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