samples/scenarios/src/main/java/org/apache/edgent/samples/scenarios/iotp/range/sensor/RangeSensor.java

/*
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you 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.
*/
package org.apache.edgent.samples.scenarios.iotp.range.sensor;

import org.apache.edgent.function.Supplier;

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.Pin;

public class RangeSensor implements Supplier<Double> {
    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private final static Double SPEED_OF_SOUND = 340.29; // speed of sound
    private final GpioPinDigitalInput echoPin;
    private final GpioPinDigitalOutput trigPin;
    private final int MAX_CYCLES = 3000;

    private final static GpioController gpio = GpioFactory.getInstance();

    public RangeSensor(Pin echoPin, Pin trigPin) {
        this.echoPin = gpio.provisionDigitalInputPin(echoPin);
        this.trigPin = gpio.provisionDigitalOutputPin(trigPin);
        this.trigPin.low();
    }

    /*
     * Get the distance in cm. Distance is (timeOfSignal * SpeedOfSound) / 2
     * (divide by 10000 is for units)
     */
    public Double getDistance() {
        triggerSensor();

        long reboundTimeMicroSeconds = getSignalDuration();
        Double distance = reboundTimeMicroSeconds * SPEED_OF_SOUND / (2 * 10000); // gives
                                                                                  // distance
                                                                                  // in
                                                                                  // cm
        return distance;
    }

    /*
     * Send signal for 10 microseconds
     */
    private void triggerSensor() {
        this.trigPin.high();
        try {
            Thread.sleep(0, 10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        this.trigPin.low();
    }

    /*
     * Measure signal duration
     */
    private long getSignalDuration() {
        int cycles = 0;
        long start = System.nanoTime();

        while (this.echoPin.isLow() && cycles < MAX_CYCLES) {
            // only iterate through MAX_CYCLES times before giving up
            start = System.nanoTime();
            cycles++;
        }

        cycles = 0;

        while (this.echoPin.isHigh() && cycles < MAX_CYCLES) {
            // only iterate through MAX_CYCLES times before giving up
            cycles++;
        }
        long end = System.nanoTime();
        long microSeconds = (long) Math.ceil((end - start) / 1000.0);
        return microSeconds;
    }

    @Override
    public Double get() {
        return getDistance();
    }

}