Blinks a light softly by scaling analog values (demo at http://i.imgur.com/dz3ZJUF.gif)

softblink.ino

// This will cause the LED in port D0 to blink softly ("breathe") like the built-in status indicator does when connected to the Internet.
// I used a 20 second delay between increments, which seems to be sufficient for a smooth increase or decrease in brightness.
// To modify the speed at which the light blinks, change the increment and decrement of output (lines 16 and 24); default is 3 for both.

int led = D0; // Attached light
int output = 0; // Power to light
bool increasing = true; // Decides whether to increase or decrease power to the light

void setup() {
    pinMode(led, OUTPUT); // LED will be used for output (light)
}

void loop() {
    if(increasing) {
        analogWrite(led, output);
        output += 3; // Change this to change the blinking speed
        delay(20);
        
        if(output >= 255){ // Upper threshold
           increasing = false; // Start decrementing power
        }
    } else {
        analogWrite(led, output);
        output -= 3; // Change this to change the blinking speed (usually the same for decrement as is for increment, but that is not required)
        delay(20);
        
        if(output <= 0) { // Lower threshold
            increasing = true; // Start incrementing power
        }
    }
}