Android Things之闪烁的LED灯

2017-09-07 本文已影响174人 Yanqilong

上节讲了开发Android Things应用时常用的一些操作命令，不明白的可以查看http://www.jianshu.com/p/08f6785ff5aa

本节内容讲如何控制LED灯并闪烁，先来看下电路连接图和实际效果图

电路连接图

实际效果图

准备材料

开发板
面包板
电阻
两根公-母杜邦线
LED灯

按效果图接好各个组件

创建AS工程并配置项目

在模块下的build.gradle需引入Android Things

provided 'com.google.android.things:androidthings:0.5.1-devpreview'

应用必须引入Android Things库，在<application>节点下配置以下代码

<uses-library android:name="com.google.android.things"/>

在AndroidManifest.xml中，往<activity>节点中配置一个<intent-filter>过滤器，表示设备启动时需要启动的类

<intent-filter>
    <action android:name="android.intent.action.MAIN"/>
    <category android:name="android.intent.category.IOT_LAUNCHER"/>
    <category android:name="android.intent.category.DEFAULT"/>
</intent-filter>

具体代码

<application android:allowBackup="true" android:icon="@android:drawable/sym_def_app_icon"
        android:label="@string/app_name">
        <uses-library android:name="com.google.android.things"/>
        <activity android:name=".BlinkActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>

            <!-- 设备启动后自动打开Activity -->
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>
                <category android:name="android.intent.category.IOT_LAUNCHER"/>
                <category android:name="android.intent.category.DEFAULT"/>
            </intent-filter>
        </activity>
    </application>

获取开发板的名称

Android Things支持的开发板有多种类型，所以引脚对应的名称也不一样，所以第一步先获取开发板的名称

private static String getBoardVariant() {
        if (!sBoardVariant.isEmpty()) {
            return sBoardVariant;
        }
        sBoardVariant = Build.DEVICE;
        Log.e(TAG, sBoardVariant);
        if (sBoardVariant.equals(DEVICE_EDISON)) {
            PeripheralManagerService pioService = new PeripheralManagerService();
            List<String> gpioList = pioService.getGpioList();
            if (gpioList.size() != 0) {
                String pin = gpioList.get(0);
                if (pin.startsWith("IO")) {
                    sBoardVariant = DEVICE_EDISON_ARDUINO;
                }
            }
        }
        return sBoardVariant;
    }

sBoardVariant是一个静态变量，代表开发板的名称，如果已经有值则返回，没有则用Build.DEVICE获取开发板名字，获取到开发板名称后，如果开发板是edison系列，需要检查引脚前缀，因为edison和edison_arduino开发板用Build.DEVICE获取的名称相同，而引脚名称却不同，所以使用PeripheralManagerService外围设备管理器调用getGpioList()获取设备所有的Gpio引脚名称，在不为空的情况下，检查引脚名称是否以IO开头，如果是，则开发板的是edison_arduino，否则是edison。如果开发板不是edison就不需要检查，Build.DEVICE获取到的名称是开发板的真实名称。

获取连接LED灯的引脚名称

上一个步骤已经获取到开发板的名称，接下来通过开发板的名称获取引脚的名称

public static String getGPIOForLED() {
        //getBoardVariant()为开发板的名称
        switch (getBoardVariant()) {
            case DEVICE_EDISON_ARDUINO:
                return "IO13";
            case DEVICE_EDISON:
                return "GP45";
            case DEVICE_JOULE:
                return "J6_25";
            case DEVICE_RPI3:
                return "BCM6";
            case DEVICE_IMX6UL_PICO:
                return "GPIO4_IO22";
            case DEVICE_IMX6UL_VVDN:
                return "GPIO3_IO06";
            case DEVICE_IMX7D_PICO:
                return "GPIO_34";
            default:
                throw new IllegalStateException("Unknown Build.DEVICE " + Build.DEVICE);
        }
    }

我所使用的开发板是树莓派，所以连接LED灯的引脚名称是BCM6，这些名称如何得知需要看开发板的电路原理图，每个引脚的名称、用途会有说明，学的越来越底层了，～.~

打开引脚

//声明外围设备管理器
PeripheralManagerService service = new PeripheralManagerService();
//引脚名称
String pinName = BoardDefaults.getGPIOForLED();
//打开引脚
mLedGpio = service.openGpio(pinName);
//设置为输出引脚并初始化为低电平
mLedGpio.setDirection(Gpio.DIRECTION_OUT_INITIALLY_LOW);
//因为初始化输出引脚为低电平，所以LED灯不会亮，这是这是为true
//后LED会亮起来
mLedGpio.setValue(true)；

如何让LED灯闪烁起来

使用异步类实现，这里使用Handler

    private Runnable mBlinkRunnable = new Runnable() {
        @Override
        public void run() {
            try {
                // 切换电平状态
                mLedState = !mLedState;
                mLedGpio.setValue(mLedState);
                Log.d(TAG, "State set to " + mLedState);
                // 每隔1000ms调用该接口
                mHandler.postDelayed(mBlinkRunnable, 1000);
            } catch (IOException e) {
                Log.e(TAG, "Error on PeripheralIO API", e);
            }
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //运行接口
        mHandler.post(mBlinkRunnable);
    }

private Handler mHandler = new Handler();

以上实例是部分代码下面贴出完整的代码
获取LED引脚名称代码

import android.os.Build;
import android.util.Log;

import com.google.android.things.pio.PeripheralManagerService;

import java.util.List;

@SuppressWarnings("WeakerAccess")
public class BoardDefaults {

    private static final String TAG = BoardDefaults.class.getName();

    private static final String DEVICE_EDISON_ARDUINO = "edison_arduino";
    private static final String DEVICE_EDISON = "edison";
    private static final String DEVICE_JOULE = "joule";
    private static final String DEVICE_RPI3 = "rpi3";
    private static final String DEVICE_IMX6UL_PICO = "imx6ul_pico";
    private static final String DEVICE_IMX6UL_VVDN = "imx6ul_iopb";
    private static final String DEVICE_IMX7D_PICO = "imx7d_pico";
    private static String sBoardVariant = "";

    /**
     * Return the GPIO pin that the LED is connected on.
     * For example, on Intel Edison Arduino breakout, pin "IO13" is connected to an onboard LED
     * that turns on when the GPIO pin is HIGH, and off when low.
     */
    public static String getGPIOForLED() {
        switch (getBoardVariant()) {
            case DEVICE_EDISON_ARDUINO:
                return "IO13";
            case DEVICE_EDISON:
                return "GP45";
            case DEVICE_JOULE:
                return "J6_25";
            case DEVICE_RPI3:
                return "BCM6";
            case DEVICE_IMX6UL_PICO:
                return "GPIO4_IO22";
            case DEVICE_IMX6UL_VVDN:
                return "GPIO3_IO06";
            case DEVICE_IMX7D_PICO:
                return "GPIO_34";
            default:
                throw new IllegalStateException("Unknown Build.DEVICE " + Build.DEVICE);
        }
    }

    private static String getBoardVariant() {
        if (!sBoardVariant.isEmpty()) {
            return sBoardVariant;
        }
        sBoardVariant = Build.DEVICE;
        Log.e(TAG, sBoardVariant);
        // For the edison check the pin prefix
        // to always return Edison Breakout pin name when applicable.
        if (sBoardVariant.equals(DEVICE_EDISON)) {
            PeripheralManagerService pioService = new PeripheralManagerService();
            List<String> gpioList = pioService.getGpioList();
            if (gpioList.size() != 0) {
                String pin = gpioList.get(0);
                if (pin.startsWith("IO")) {
                    sBoardVariant = DEVICE_EDISON_ARDUINO;
                }
            }
        }
        return sBoardVariant;
    }
}

让LED灯闪烁完整代码

/**
 * Sample usage of the Gpio API that blinks an LED at a fixed interval defined in
 * {@link #INTERVAL_BETWEEN_BLINKS_MS}.
 *
 * Some boards, like Intel Edison, have onboard LEDs linked to specific GPIO pins.
 * The preferred GPIO pin to use on each board is in the {@link BoardDefaults} class.
 *
 */
public class BlinkActivity extends Activity {
    private static final String TAG = BlinkActivity.class.getSimpleName();
    private static final int INTERVAL_BETWEEN_BLINKS_MS = 2000;

    private Handler mHandler = new Handler();
    private Gpio mLedGpio;
    private boolean mLedState = false;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.i(TAG, "Starting BlinkActivity");

        PeripheralManagerService service = new PeripheralManagerService();
        try {
            String pinName = BoardDefaults.getGPIOForLED();
            mLedGpio = service.openGpio(pinName);
            mLedGpio.setDirection(Gpio.DIRECTION_OUT_INITIALLY_LOW);
            Log.i(TAG, "Start blinking LED GPIO pin");
            // Post a Runnable that continuously switch the state of the GPIO, blinking the
            // corresponding LED
            mHandler.post(mBlinkRunnable);
        } catch (IOException e) {
            Log.e(TAG, "Error on PeripheralIO API", e);
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        // Remove pending blink Runnable from the handler.
        mHandler.removeCallbacks(mBlinkRunnable);
        // Close the Gpio pin.
        Log.i(TAG, "Closing LED GPIO pin");
        try {
            mLedGpio.close();
        } catch (IOException e) {
            Log.e(TAG, "Error on PeripheralIO API", e);
        } finally {
            mLedGpio = null;
        }
    }

    private Runnable mBlinkRunnable = new Runnable() {
        @Override
        public void run() {
            // Exit Runnable if the GPIO is already closed
            if (mLedGpio == null) {
                return;
            }
            try {
                // Toggle the GPIO state
                mLedState = !mLedState;
                mLedGpio.setValue(mLedState);
                Log.d(TAG, "State set to " + mLedState);

                // Reschedule the same runnable in {#INTERVAL_BETWEEN_BLINKS_MS} milliseconds
                mHandler.postDelayed(mBlinkRunnable, INTERVAL_BETWEEN_BLINKS_MS);
            } catch (IOException e) {
                Log.e(TAG, "Error on PeripheralIO API", e);
            }
        }
    };
}

该例子是google官方的例子，这里给出源码地址https://github.com/androidthings/sample-simplepio.git

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