PWM code Atmega32A Atmel 6.2

[Dorien]

Hi all,

For a project I need to brighten up a LED on an STK500 board via PWM. I am working with an ATMEGA32A and write the code in C (AtmelStudio 6.2). I have been doing quite a bit of research (i.e. spending hours and hours on forums and in the datasheet).
This is what I found out/came up with so far:
- the LED that is an output for PWM is OC0=PB3
- I chose to put the register TCCR0 on fast PWM, non inverted, no prescaler
- the trigger to start the PWM cycle is pressing switch 0 (this is part of the project, I have to set a trigger (alarm) to start the cycle)
- when I set OCR0 = 0 that means PWM = 0. so when I set OC0 = 115 that would be a PWM of 45% (of 255), right? I need to add 'value' to OCR0 in order to make the LED shine brighter and brighter each clockcycle, I used a for-loop for that

My question:
When I build the code in Atmel Studio it does not give an error (hurray for me , but when I flash it to the STK500 nothing happens with the LED when I press switch 0

I'll try to attach my code. Can someone give me some advice on this?

Thanks in advance!

[ag]

Hi Dorian,

I don't see any loop in your main.

Regards,

[Dorien]

Hi Ag,

you are right, I had to include the init_pwm in the main.

I changed the code a bit, but now the result is that the LED on PINB3 turns on when I flash the code. It stays on all the time.
Is that due to the fact that the calculation in the ISR happens s fast that I can't see it? Of does the program not run the ISR at all?

I want the LED to start at 0 and then become brighter and brighter , like a wake up light.

What am I doing wrong?

[ag]

Hi Dorian,

Currently, your program still does not have an endless loop in the main function. Therefore, your code only runs straight through in one shot, lighting up the LED only once and then stopping. Within the main function, you need to add an endless loop ( e.g. WHILE(1) ...) which encloses you code, so that the code which brightens up you led via PWM keeps repeating (as long as the swith is activated) over and over again.

Try folowing the code step by step using the debugger to get a better idea of what is actually going on.

Regards,

[Dorien]

Hi Ag,
I started from scratch again and will try to build my code step by step. I encounter a problem with this small piece of code:

#include <avr/io.h>
#include <util/delay.h>

int main(void)
{
DDRA &= ~(1<<PA0);//input
DDRB = (1<<PB3);//output

while(1)
{

if((PINA & (1<<PA0)) == 0)//press switch A0 starts toggling LED 3
{
PORTB ^= (1<<PB3); //toggle LED3
}
_delay_ms(500);
}
}

Can you explain why the LED3 burns constantly? I expected it to be off till switch A0 is activated and than toggle the LED (this works well).

[ag]

Hi Dorian,

At the start of your loop, PIN 0 of PORTA is in it´s initial state. Since you have not set the internal pull up resisiter for this pin, that state is logical 0. I assume you have not connected an external pull up resistor to that pin, setting it to logical 1, otherwise your LED3 would not be lighting until the switch is activated.

Try setting the internal pull up resistors for PORTA and see if that helps.

Regards,

[3dtech]

thanks for this valuable information.