ATtiny13 – hardware PWM

This article shows how to make an ATtiny13 to generate hardware PWM (Pulse Width Modulation) signal. The example code uses timer in Fast PWM mode (WGM02:0 = 3, see manual section 11.7.3). In this mode, by setting the COM0A1:0 bits to one, the compare unit allows generation of PWM waveforms on the AC0A pin (PB0) with duty resolution 0..255. The presented example can operate on few frequencies: 4.687kHz, 585Hz, 73Hz, 18Hz, 4Hz (@1.2MHz). If you need higher PWM frequencies then set fuse bits to run ATtiny13 with 9.6MHz clock source. The example code is on Github, click here.

Parts Required

• ATtiny13  – i.e. MBAVR-1 development board

Circuit Diagram

Software

This code is written in C and can be compiled using the avr-gcc. All information about how to compile this AVR project is here.

/**
 * Copyright (c) 2019, Łukasz Marcin Podkalicki <lpodkalicki@gmail.com>
 * ATtiny13/031
 * Example of hardware Fast PWM.
 * Features:
 * - PWM duty resolution: 0..255
 * - PWM frequencies (@1.2MHz): 4.687kHz, 585Hz, 73Hz, 18Hz, 4Hz 
 */

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

#define N_1    (_BV(CS00))
#define N_8    (_BV(CS01))
#define N_64   (_BV(CS01)|_BV(CS00))
#define N_256  (_BV(CS02))
#define N_1024 (_BV(CS02)|_BV(CS00))

static void
pwm_init(void)
{
    DDRB |= _BV(PB0); // set PWM pin as OUTPUT
    TCCR0A |= _BV(WGM01)|_BV(WGM00); // set timer mode to FAST PWM
    TCCR0A |= _BV(COM0A1); // connect PWM signal to pin (AC0A => PB0)
}

/* When timer is set to Fast PWM Mode, the freqency can be
calculated using equation: F = F_CPU / (N * 256) 
Posible frequencies (@1.2MHz):
 -> F(N_1) = 4.687kHz
 -> F(N_8) = 585Hz
 -> F(N_64) = 73Hz
 -> F(N_256) = 18Hz
 -> F(N_1024) = 4Hz */
static void
pwm_set_frequency(uint32_t N)
{

    TCCR0B = (TCCR0B & ~((1<<CS02)|(1<<CS01)|(1<<CS00))) | N; // set prescaler
}

static void
pwm_set_duty(uint8_t duty)
{

    OCR0A = duty; // set the OCRnx
}

static void
pwm_stop(void)
{

    TCCR0B &= ~((1<<CS02)|(1<<CS01)|(1<<CS00)); // stop the timer
}

int
main(void)
{
    uint8_t duty = 0;

    /* setup */
    pwm_init();
    pwm_set_frequency(N_1);

    /* loop */
    while (1) {
        pwm_set_duty(duty++);
        _delay_ms(100);
    }
}