\nThis is done with Pulse-width modulation (PWM)<\/strong>. PWM is a “modulation technique that conforms the width of the pulse, formally the pulse duration, based on modulator signal information.” (Wikipedia<\/a>).<\/p>\n
In a nutshell<\/strong>: Basically there are two ways to create PWM:<\/strong><\/p>\n Hardware PWM<\/strong><\/p>\n BUT:<\/p>\n Software PWM<\/strong><\/p>\n BUT:<\/p>\n In other words: HW PWM is clearly prefered!<\/p>\n But unfortunately there is only one HW PWM pin (#18) available on the Rasperry Pis GPIO header (also its shared with the Audio system. That means that you can’t use PWM or Servo output and play audio through the 3.5mm jack at the same time).<\/p>\n If a RasPi project needs more than 1 PWM it has to use soft-pwm. Pi4J provides a class called “SoftPwm”. As it uses wiringPi functions, the GPIO subsytem has to be initialzed first. Here is a simple example:<\/p>\n [java] public static void main(String[] args) throws InterruptedException {<\/p>\n \/\/ initialize wiringPi library \/\/ create soft-pwm pins (min=0 ; max=100) IntegerProperty value1 = new SimpleIntegerProperty(); \/\/ continuous loop Works! 3 x optical coupler + RGB LED stripe triggered by JavaFX UI contolled SoftPwms:<\/p>\n
\nThe average value of voltage is depending on the frequency the load is switched on and off.<\/p>\n\n
\n
\n
\n
\nHowever thank god all the hard work is almost done by using Gordon Henderson’s wiringPi-lib and its Java-API Pi4J<\/a>.<\/p>\n
\nTherefore the programm has to executed as “sudo”!<\/p>\n
\npublic class WiringPiSoftPWMExample {<\/p>\n
\n Gpio.wiringPiSetup();<\/p>\n
\n SoftPwm.softPwmCreate(0, 0, 100);<\/p>\n
\n value1.addListener((ObservableValue observable, Number oldValue, Number newValue) -> {
\n SoftPwm.softPwmWrite(0, newValue.intValue());
\n });<\/p>\n
\n while (true) {
\n \/\/ fade LED to fully ON
\n for (int i = 0; i <= 100; i++) {\n value1.set(i);\n Thread.sleep(25);\n }\n\n \/\/ fade LED to fully OFF\n for (int i = 100; i >= 0; i–) {
\n value1.set(i);
\n Thread.sleep(25);
\n }
\n }
\n }
\n}
\n[\/java]<\/p>\n![\"LED](\"http:\/\/www.jensd.de\/wordpress\/wp-content\/uploads\/2014\/04\/LED-blink.png\")
<\/a><\/p>\n
\nWhat’s next?<\/strong><\/p>\n![\"IMG_3176\"](\"http:\/\/www.jensd.de\/wordpress\/wp-content\/uploads\/2014\/04\/IMG_3176.jpg\")
<\/a><\/p>\n