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Fading LED default test sketch (February 12, 2009)
For some time now, every Arduino bootloaded ATmega we've shipped has come with a default testing sketch that slowly pulses the LED on and off in a cyclic fashion.
A "fading" sketch using hardware PWM is included in the IDE distribution under Examples→Analog→Fading to fade an LED, but the Pin 13 status LED isn't connected to a hardware PWM pin.
The answer is to abuse the delayMicroseconds call to create crude software PWM. By setting the pin high; delaying; setting the pin off; and delaying for a different period, we can change the brightness simply by altering the delay.
One catch to this approach, is if you use purely the on/off delay to control the PWM speed, you're left with either a very fast fade or an unsettling flashing. Instead we keep the delay between 4 and 250 µs (about 3 to 4kHz) and add an additional loop around each on/off loop to set the fading speed. --You can't set the delayMicroseconds code to 0 or you'll get an unexpectedly long delay.
Finally, we use the serial port to output a rising count, just to ensure the serial port works.
// by Spiffed <https://spiffie.org/>;
// original by BARRAGAN <;
int value = 0;
int rep = 0;
int ledpin = 13;
int count = 0; // light connected to digital pin 9
void setup()
{
Serial.begin(9600);
pinMode(ledpin,OUTPUT);
}
void loop()
{
for(value = 4 ; value <= 250; value++) // fade in (from min to max)
{
for(rep=0;rep <= 10;rep++){
digitalWrite(ledpin, HIGH); // sets the value (range from 0 to 255)
delayMicroseconds(value); // waits for 30 milli seconds to see the dimming effect
digitalWrite(ledpin, LOW);
delayMicroseconds((255-value));
}
}
Serial.println(count);
count++;
for(value = 250; value >=4; value--) // fade out (from max to min)
{
for(rep=0;rep <= 10;rep++){
digitalWrite(ledpin, HIGH); // sets the value (range from 0 to 255)
delayMicroseconds(value); // waits for 30 milli seconds to see the dimming effect
digitalWrite(ledpin, LOW);
delayMicroseconds(255-value);
}
}
}
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Posted by spiffed at February 12, 2009 11:11 AM