com.pi4j.wiringpi

Class SoftPwm

java.lang.Object

com.pi4j.wiringpi.SoftPwm

public class SoftPwm
extends Object

WiringPi includes a software-driven PWM handler capable of outputting a PWM signal on any of the Raspberry Pi's GPIO pins.

There are some limitations. To maintain a low CPU usage, the minimum pulse width is 100uS. That combined with the default suggested range of 100 gives a PWM frequency of 100Hz. You can lower the range to get a higher frequency, at the expense of resolution, or increase to get more resolution, but that will lower the frequency. If you change the pulse-width in the drive code, then be aware that at delays of less than 100uS wiringPi does it in a software loop, which means that CPU usage will rise dramatically, and controlling more than one pin will be almost impossible.

Also note that while the routines run themselves at a higher and real-time priority, Linux can still affect the accuracy of the generated signal.

However, within these limitations, control of a light/LED or a motor is very achievable.

You must initialize wiringPi with one of wiringPiSetup() or wiringPiSetupGpio() functions beforehand. wiringPiSetupSys() is not fast enough, so you must run your programs with sudo.

Before using the Pi4J library, you need to ensure that the Java VM in configured with access to the following system libraries:

• pi4j
• wiringPi
• pthread

This library depends on the wiringPi native system library.
(developed by Gordon Henderson @ https://projects.drogon.net/)

Author:

Robert Savage (http://www.savagehomeautomation.com)

See Also:

http://www.pi4j.com/, https://projects.drogon.net/raspberry-pi/wiringpi/software-pwm-library/

Method Summary

Methods

Modifier and Type	Method and Description
static int	softPwmCreate(int pin, int value, int range) int softPwmCreate (int pin, int initialValue, int pwmRange);
static void	softPwmWrite(int pin, int value) void softPwmWrite (int pin, int value);

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

softPwmCreate

public static int softPwmCreate(int pin,
                int value,
                int range)

int softPwmCreate (int pin, int initialValue, int pwmRange);

This creates a software controlled PWM pin. You can use any GPIO pin and the pin numbering will be that of the wiringPiSetup function you used. Use 100 for the pwmRange, then the value can be anything from 0 (off) to 100 (fully on) for the given pin.

Parameters:

pin - The GPIO pin to use as a PWM pin.

value - The value to initialize the PWM pin (between 0 (off) to 100 (fully on))

range - The maximum range. Use 100 for the pwmRange.

Returns:

The return value is 0 for success. Anything else and you should check the global errno variable to see what went wrong.

See Also:

https://projects.drogon.net/raspberry-pi/wiringpi/software-pwm-library/

softPwmWrite

public static void softPwmWrite(int pin,
                int value)

void softPwmWrite (int pin, int value);

This updates the PWM value on the given pin. The value is checked to be in-range and pins that haven't previously been initialized via softPwmCreate will be silently ignored.

Parameters:

pin - The GPIO pin to use as a PWM pin.

value - The value to initialize the PWM pin (between 0 (off) to 100 (fully on))

See Also:

https://projects.drogon.net/raspberry-pi/wiringpi/software-pwm-library/