何謂輕觸開關

輕觸開關英文為 Tactile[ˋtæktɪl] push switch, 就是按下後會通電, 放開後就斷電.  所以可以在按下開關後, 灌入3.3V電壓, 讓GPIO偵測有電壓進來, 然後觸發GPIO的監聽程式, 進而引發GpioPinDigitalStateChangeEvent 事件, 然後由此事件去執行某項工作.

輕觸開關結構圖

TPS開關的結構圖如下所式, 未按下時, 12未通電, 34也未通電. 按下後12通電, 34也通電.

注意事項

輕觸開關需將GPIO更改為Input, 這就不是開玩笑了. 因為會把3.3V的電壓灌進GPIO之中, 若沒有加入電阻的話, 電流過大, 會造成樹莓派的板子燒毀.

一般建議會在把電流灌進GPIO的針腳前, 加上一顆1KΩ的電阻. 經V=IR計算, 3.3=I*1000, 灌進GPIO針腳的電流I值為 3.3mA, 這就蠻小的了.  反正GPIO是要偵測是否有3.3V的電壓進來, 所以電流越小越好.

另外為了加一層防護措施, 也要加一條線路到GND, 中間也要加入一個10KΩ的電阻, 這是為了Pull Up Resistor 的連接方式

連接方式如下所示

Pull Down Resistor

Pull  Up Resistor

那到底要幹什麼

底下程式, 使用二顆輕觸開關, buttonLed按一下點亮Led, 再點一下關掉Led. buttonPower則會關閉整個程式

首先, GPIO0為程式關閉按鈕, GPIO1為Led燈的開關, GPIO2為Led的電源.

GPIO0及GPIO1設定為Input :
gpioController.provisionDigitalInputPin(RaspiPin.GPIO_00, PinPullResistance.PULL_DOWN);

然後二個GPIO 使用 AddListener(GpioPinListenerDigital) 監控按鈕的狀況,  當按鈕為High時, 執行要作的任務

程式結束前, 請使用 removeAllListeners()將監控程式移除

PowerSwitch.java

package powerswitch;
import com.pi4j.io.gpio.GpioController;
import com.pi4j.io.gpio.GpioFactory;
import com.pi4j.io.gpio.GpioPinDigitalInput;
import com.pi4j.io.gpio.GpioPinDigitalOutput;
import com.pi4j.io.gpio.PinPullResistance;
import com.pi4j.io.gpio.PinState;
import com.pi4j.io.gpio.RaspiPin;
import com.pi4j.io.gpio.event.GpioPinDigitalStateChangeEvent;
import com.pi4j.io.gpio.event.GpioPinListenerDigital;
import java.util.logging.Level;
import java.util.logging.Logger;
public class PowerSwitch {
    static Led led1;
    static boolean closeFlag=false;
    static boolean busy=false;
    public static void main(String[] args) {
        GpioController gpioController=GpioFactory.getInstance();
        G.buttonPower=gpioController.provisionDigitalInputPin(RaspiPin.GPIO_00, PinPullResistance.PULL_DOWN);
        G.buttonLed=gpioController.provisionDigitalInputPin(RaspiPin.GPIO_01, PinPullResistance.PULL_DOWN);
        G.pinLed=gpioController.provisionDigitalOutputPin(RaspiPin.GPIO_03, "LED", PinState.LOW);
        G.buttonPower.addListener(new GpioPinListenerDigital(){
            @Override
            public void handleGpioPinDigitalStateChangeEvent(GpioPinDigitalStateChangeEvent event) {
                PinState state=event.getState();
                if(state.isHigh()){
                    closeFlag=true;
                }
            }
        });
        G.buttonLed.addListener(new GpioPinListenerDigital(){
            @Override
            public void handleGpioPinDigitalStateChangeEvent(GpioPinDigitalStateChangeEvent event) {
                if(busy)return;
                busy=true;
                PinState state=event.getState();
                if(state.isHigh()){
                    if(led1==null){
                        led1=new Led();
                        led1.start();
                    }
                    else{
                        led1.close();
                        led1=null;
                    }
                }
                busy=false;
            }
        });
        while(!closeFlag){
            try {Thread.sleep(500);} 
            catch (InterruptedException ex) {}
        }
        G.buttonPower.removeAllListeners();
        G.buttonLed.removeAllListeners();
        if(led1!=null)led1.close();
        gpioController.shutdown();
        System.out.println("Game over");
    }
}
class Led extends Thread{
    private boolean runFlag=true;
    public void run(){
        while(runFlag){
            G.pinLed.pulse(500);
            G.delay(550);
        }
    }
    public void close(){
        runFlag=false;
        G.pinLed.setState(PinState.LOW);
        this.interrupt();
    }
}



G.java如下

package powerswitch;
import com.pi4j.io.gpio.GpioPinDigitalInput;
import com.pi4j.io.gpio.GpioPinDigitalOutput;
public class G {
    public static GpioPinDigitalInput buttonPower, buttonLed;
    public static GpioPinDigitalOutput pinLed;
    public static void delay(int t){
        try {Thread.sleep(t);} 
        catch (InterruptedException ex) {}
    }
}