android_things_09_pwm 控制舵机旋转

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adb 连接树莓派，运行程序控制舵机旋转。

效果图

连接舵机

1. 树莓派5V电源线连接舵机的中间的红线（不同的舵机正负极连接线可能不一样，需要正确连接，否则可能烧毁舵机）
2. 树莓派GND连接舵机棕色的负极
3. 树莓派 PWM输出线 连接舵机橙色的线

核心代码

在子线程中动态改变脉冲

  private Runnable mChangePWMRunnable = new Runnable() {
        @Override
        public void run() {
            // Exit Runnable if the port is already closed
            if (mPwm == null) {
                Log.w(TAG, "Stopping runnable since mPwm is null");
                return;
            }

            // Change the duration of the active PWM pulse, but keep it between the minimum and
            // maximum limits.
            // The direction of the change depends on the mIsPulseIncreasing variable, so the pulse
            // will bounce from MIN to MAX.
            if (mIsPulseIncreasing) {
                mActivePulseDuration += PULSE_CHANGE_PER_STEP_MS;
            } else {
                mActivePulseDuration -= PULSE_CHANGE_PER_STEP_MS;
            }

            // Bounce mActivePulseDuration back from the limits
            if (mActivePulseDuration > MAX_ACTIVE_PULSE_DURATION_MS) {
                mActivePulseDuration = MAX_ACTIVE_PULSE_DURATION_MS;
                mIsPulseIncreasing = !mIsPulseIncreasing;
            } else if (mActivePulseDuration < MIN_ACTIVE_PULSE_DURATION_MS) {
                mActivePulseDuration = MIN_ACTIVE_PULSE_DURATION_MS;
                mIsPulseIncreasing = !mIsPulseIncreasing;
            }

            Log.d(TAG, "Changing PWM active pulse duration to " + mActivePulseDuration + " ms");

            try {

                // Duty cycle is the percentage of active (on) pulse over the total duration of the
                // PWM pulse
                mPwm.setPwmDutyCycle(100 * mActivePulseDuration / PULSE_PERIOD_MS);

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

获取连接PWM的引脚端口，不同设备对应的端口名称不一样注意区分

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 preferred PWM port for each board.
     */
    public static String getPWMPort() {
        switch (Build.DEVICE) {
            case DEVICE_RPI3:
                return "PWM0";
            case DEVICE_IMX6UL_PICO:
                return "PWM7";
            case DEVICE_IMX7D_PICO:
                return "PWM1";
            default:
                throw new IllegalStateException("Unknown Build.DEVICE " + Build.DEVICE);
        }
    }
}

初始化设置并开启子线程

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

        try {
            String pinName = BoardDefaults.getPWMPort();
            mActivePulseDuration = MIN_ACTIVE_PULSE_DURATION_MS;

            mPwm = PeripheralManager.getInstance().openPwm(pinName);

            // Always set frequency and initial duty cycle before enabling PWM
            mPwm.setPwmFrequencyHz(1000 / PULSE_PERIOD_MS);
            mPwm.setPwmDutyCycle(mActivePulseDuration);
            mPwm.setEnabled(true);

            // Post a Runnable that continuously change PWM pulse width, effectively changing the
            // servo position
            Log.d(TAG, "Start changing PWM pulse");
            mHandler.post(mChangePWMRunnable);
        } catch (IOException e) {
            Log.e(TAG, "Error on PeripheralIO API", e);
        }
    }

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