PWM and 0% duty cycle - not happening

Projects Programming
1

I am having some issues with trying to get a 0% duty cycle using Timer2 in Fast PWM mode. I am using the example from http://arduino.cc/en/Tutorial/SecretsOfArduinoPWM...

  TCCR2A = _BV(COM2A1) | _BV(COM2B1) | _BV(WGM21) | _BV(WGM20);
  TCCR2B = _BV(CS22);
  OCR2A = 0;
  OCR2B = 0;

I have LEDs (with current limiting resistors) on pin 3 and 11. However, when I run the code, they glow. When I ramp up the duty cycle, they get brighter as expected. Also, shortening the duty cycle, they dim. However, setting OCR2A or B to 0 still generates a pulse. Is there a way around this issue short of changing the pin to input mode at 0? I have seen a 0% duty cycle with the phase corrected mode. Just can't get that in Fast PWM mode.

2

I had a similar issue and that's how I fixed it. But I used the following code controlling the duty cycle with a potentiometer....

const int led = 3;        //set digital pin 3 as led pin
const int pot = A0;   //set analog pin 0 as input
int pwm_dc =0;       //set a value to control duty cycle

void setup();
{
pinMode(led, OUTPUT);     //set led(pin 3) as output

TCCR3A = _BV(COM3A0) | _BV(COM3B1) | _BV(WGM31);  //Set PWM frequency to 245hz on pin 3
  TCCR3B = _BV(CS21) | _BV(CS20);
}

void loop()
{
pwm_dc = map(analogRead(po)0,1023,0,255); //read anaolg pin and map it's value

analogWrite(led,pwm_dc);      //writes pwm to led depending on pot value "pwm_dc"
}

This code will vary the brightness of the led depending on the output of the potentiometer.

NOTE: this is on Timer3 using a Mega 2560. You can use whatever timer you prefer as long as it doesn't affect millis() or micros().

Bill