android_things_08_led

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android things 点亮LED

adb 连接到树莓派，运行点亮led程序

效果图

连接led

1. 从树莓派的一个GPIO引脚（Pin31-BCM6）串联一个电阻（300Ω~1KΩ），连接LED正极（LED灯的长脚）
2. 树莓派负极连接LED负极

核心代码

在子线程中每隔一秒切换下I/O电平信号，刷新LED状态

    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);
            }
        }
    };

获取连接LED的引脚端口，不同设备对应的端口名称不一样注意区分

@SuppressWarnings("WeakerAccess")
public class BoardDefaults {
    private static final String DEVICE_RPI3 = "rpi3";
    private static final String DEVICE_IMX6UL_PICO = "imx6ul_pico";
    private static final String DEVICE_IMX7D_PICO = "imx7d_pico";

    /**
     * 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 (Build.DEVICE) {
            case DEVICE_RPI3:
                return "BCM6";
            case DEVICE_IMX6UL_PICO:
                return "GPIO4_IO22";
            case DEVICE_IMX7D_PICO:
                return "GPIO2_IO02";
            default:
                throw new IllegalStateException("Unknown Build.DEVICE " + Build.DEVICE);
        }
    }
}

初始化设置拉低电平信号，开启信号切换线程。

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

        try {
            String pinName = BoardDefaults.getGPIOForLED();
            mLedGpio = PeripheralManager.getInstance().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);
        }
    }

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