Hi,
I need to create 10 different PWM duyt cycle with a MEGA board. As the controller doesn't have so many different PWM duyt cycles I tried to do that by reading the TIMER1 register. I used the onboard LED so everyone reading this topic can try it easily.
I got avery uneven response and the LED is not having a conxtant PWM but having some light flickerings visible... :~ That shouldn't happen, right?
Here is my code
#include <avr/io.h>
#include <avr/interrupt.h>
void setup() {
// initialize the digital pin as an output.
DDRB= B11111111; // set PORTB (digital 13-8) to outputs
cli(); // disable global interrupts
TCCR1A = 0; // set entire TCCR1A register to 0
TCCR1B = 0; // same for TCCR1B
TCCR1B |= (1 << CS10); // Set CS10 bit only for prescaler 1
sei(); // enable global interrupts:
}
void loop() {
if (TCNT1 < 5){
PORTB=B10000000;
}
if (TCNT1 > 20000){
PORTB=B00000000;
}
}
soulid:
I need to create 10 different PWM duyt cycle with a MEGA board.
soulid:
Issue is the resolution which is fixed at 8 bit. We need a resolution of more than 10bit...
These two quotes seem inconsistent. Are you trying to output one of ten different duty cycles (easily done with 8-bit resolution) or a thousand different duty cycles (which would need 10-bit resolution).
That can happen: let's say that your counter overflows at the end of the loop. By the time it is tested for "TCNT1 < 5", however, the timer has advanced beyond 5 and the sentence in the "if" statement (" PORTB=B10000000; ") is never executed -> that cycle is more than 64k ticks -> light stays off twice as long.
You can test this by changing 5 to 50 or 500 (to reduce / eliminate the chance of this happening and your light will never flicker. Alternatively, you can increase the prescaler as well.
Hi dhenry- I am impressed. You got the failure. changeing the value to 50 gives an even result although it is niot accurate enough. I need to think ybout other solutions. This single PWM was intendet to be first out of 10 different PWMs.
