Quick Android Things demo using ObjectAnimator to animate the brightness of a PWM output. This example uses a BounceInterpolator to create a flickering effect on an LED (like a candle).

FlickerActivity.java

/*
 * Copyright 2016 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import android.animation.ObjectAnimator;
import android.animation.ValueAnimator;
import android.app.Activity;
import android.os.Bundle;
import android.util.FloatProperty;
import android.util.Log;
import android.view.animation.BounceInterpolator;

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

import java.io.IOException;

public class FlickerActivity extends Activity {
    private static final String TAG = "FlickerActivity";

    // PWM output pin names (Edison)
    private static final String YELLOW_PWM = "IO6";
    private static final String ORANGE_PWM = "IO5";

    private static final int DURATION_MS = 350;
    private static final int DELAY_MS = 150;

    private PeripheralManagerService mService = new PeripheralManagerService();
    private Pwm mYellowLed, mOrangeLed;
    private ObjectAnimator mYellowFlame, mOrangeFlame;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        try {
            mYellowLed = openLed(YELLOW_PWM);
            mOrangeLed = openLed(ORANGE_PWM);
        } catch (IOException e) {
            Log.w(TAG, "Unable to open LED connections", e);
        }

        // Create an run the flicker animations
        mYellowFlame = animateFlicker(mYellowLed, 0);
        mOrangeFlame = animateFlicker(mOrangeLed, DELAY_MS);
        mYellowFlame.start();
        mOrangeFlame.start();
    }

    @Override
    public void onDestroy() {
        super.onDestroy();

        mYellowFlame.cancel();
        mOrangeFlame.cancel();

        try {
            closeLed(mYellowLed);
            closeLed(mOrangeLed);
        } catch (IOException e) {
            Log.w(TAG, "Unable to close LED connections", e);
        }
    }

    // Create a new LED connection
    private Pwm openLed(String name) throws IOException {
        Pwm led = mService.openPwm(name);
        led.setPwmFrequencyHz(240.0f);
        led.setPwmDutyCycle(25.0);
        led.setEnabled(true);

        return led;
    }

    // Close an LED connection
    private void closeLed(Pwm pwm) throws IOException {
        if (pwm != null) {
            pwm.setEnabled(false);
            pwm.close();
        }
    }

    // Create an animation that bounces, using a flicker effect
    private ObjectAnimator animateFlicker(Pwm led, long delay) {
        ObjectAnimator animator = ObjectAnimator
                .ofFloat(led, new BrightnessProperty(), 100, 25)
                .setDuration(DURATION_MS + delay);

        animator.setInterpolator(new BounceInterpolator());
        animator.setRepeatMode(ValueAnimator.REVERSE);
        animator.setRepeatCount(ValueAnimator.INFINITE);

        return animator;
    }

    /**
     * Property used to animate the "brightness" of an
     * LED as the duty cycle of a PWM.
     */
    private class BrightnessProperty extends FloatProperty<Pwm> {
        private static final String TAG = "BrightnessProperty";

        // Cache the last set value since PWM can't report its state
        private float mValue;

        BrightnessProperty() {
            super("PWM Brightness");
        }

        @Override
        public void setValue(Pwm pwm, float value) {
            mValue = Math.max(0f, Math.min(value, 100f));
            try {
                pwm.setPwmDutyCycle(mValue);
            } catch (IOException e) {
                Log.w(TAG, "Unable to set PWM duty cycle", e);
            }
        }

        @Override
        public Float get(Pwm pwm) {
            // We can't ask PWM for its current duty value
            return mValue;
        }
    }
}