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:
This library depends on the wiringPi native system library. (developed by Gordon Henderson @ http://wiringpi.com/)
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 |
softPwmStop(int pin)
/**
|
static void |
softPwmWrite(int pin,
int value)
void softPwmWrite (int pin, int value);
|
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.
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.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.
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))public static void softPwmStop(int pin)
void softPwmStop (int pin);
This stops the software emulated PWM driver/thread for the given pin.
pin
- The GPIO pin to use as a PWM pin.Copyright © 2012–2019 Pi4J. All rights reserved.