pwm.c

Shows how to use PWM to control GPIO pins

// pwm.c
//
// Example program for bcm2835 library
// Shows how to use PWM to control GPIO pins
//
// After installing bcm2835, you can build this 
// with something like:
// gcc -o pwm pwm.c -l bcm2835 
// sudo ./pwm
//
// Or you can test it before installing with:
// gcc -o pwm -I ../../src ../../src/bcm2835.c pwm.c
// sudo ./pwm
//
// Connect an LED between GPIO18 (pin 12) and GND to observe the LED changing in brightness
//
// Author: Mike McCauley
// Copyright (C) 2013 Mike McCauley
// $Id: RF22.h,v 1.21 2012/05/30 01:51:25 mikem Exp $
 
#include <bcm2835.h>
#include <stdio.h>
 
// PWM output on RPi Plug P1 pin 12 (which is GPIO pin 18)
// in alt fun 5.
// Note that this is the _only_ PWM pin available on the RPi IO headers
#define PIN RPI_GPIO_P1_12
// and it is controlled by PWM channel 0
#define PWM_CHANNEL 0
// This controls the max range of the PWM signal
#define RANGE 1024
 
int main(int argc, char **argv)
{
    if (!bcm2835_init())
        return 1;
 
    // Set the output pin to Alt Fun 5, to allow PWM channel 0 to be output there
    bcm2835_gpio_fsel(PIN, BCM2835_GPIO_FSEL_ALT5);
 
    // Clock divider is set to 16.
    // With a divider of 16 and a RANGE of 1024, in MARKSPACE mode,
    // the pulse repetition frequency will be
    // 1.2MHz/1024 = 1171.875Hz, suitable for driving a DC motor with PWM
    bcm2835_pwm_set_clock(BCM2835_PWM_CLOCK_DIVIDER_16);
    bcm2835_pwm_set_mode(PWM_CHANNEL, 1, 1);
    bcm2835_pwm_set_range(PWM_CHANNEL, RANGE);
 
    // Vary the PWM m/s ratio between 1/RANGE and (RANGE-1)/RANGE
    // over the course of a a few seconds
    int direction = 1; // 1 is increase, -1 is decrease
    int data = 1;
    while (1)
    {
        if (data == 1)
            direction = 1;   // Switch to increasing
        else if (data == RANGE-1)
            direction = -1;  // Switch to decreasing
        data += direction;
        bcm2835_pwm_set_data(PWM_CHANNEL, data);
        bcm2835_delay(1);
    }
 
    bcm2835_close();
    return 0;
}