Cfrgtkky

I am using Apache Edgent (Java framework) to poll values from a HCSR04 ultrasonic sensor on a Raspberry Pi every 3 seconds. I use a filter to not get values from 50cm to 80cm.

    UltrasonicStream sensor = new UltrasonicStream();

    DirectProvider dp = new DirectProvider();

    Topology topology = dp.newTopology();

    TStream<Double> tempReadings = topology.poll(sensor, 3, TimeUnit.SECONDS);

    TStream<Double> filteredReadings = tempReadings.filter(reading -> reading < 50 || reading > 80);

    System.out.println("filter added: tempReadings.filter(reading -> reading < 50 || reading > 80);");

    filteredReadings.print();

    dp.submit(topology);

I want to show some message when the values are filtered. When the values do not match with my filter I can poll them, but when they match I am not returning, that is ok. However, I want just to show that a value was filtered using Apache Edgent libraries. I know that I can do something on the public double get() method, but I wonder if I could do this trick with some method of the Apache Edgent.

public class UltrasonicStream implements Supplier {

private static final long serialVersionUID = -6511218542753341056L;



private static GpioPinDigitalOutput sensorTriggerPin;

private static GpioPinDigitalInput sensorEchoPin;

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

private double currentDistance = -1.0;



/**

 * The HCSR04 Ultrasonic sensor is connected on the physical pin 16 and 18 which

 * correspond to the GPIO 04 and 05 of the WiringPi library.

 */

public UltrasonicStream() {

    // Trigger pin as OUTPUT

    sensorTriggerPin = gpio.provisionDigitalOutputPin(RaspiPin.GPIO_04);

    // Echo pin as INPUT

    sensorEchoPin = gpio.provisionDigitalInputPin(RaspiPin.GPIO_05, PinPullResistance.PULL_DOWN);

}



/**

 * This is the override method of the Supplier interface from Apache Edgent

 */

@Override

public Double get() {

    try {

        System.out.print("Distance in centimeters: ");

        currentDistance = getDistance();

    } catch (InterruptedException e) {

        // TODO Auto-generated catch block

        e.printStackTrace();

    }

    return currentDistance;

}



/**

 * Retrieve the distance measured by the HCSR04 Ultrasonic sensor connected on a

 * Raspberry Pi 3+B

 * 

 * @return the distance in centimeters

 * @throws InterruptedException

 */

public double getDistance() throws InterruptedException {



    double distanceCM = -1;

    try {

        // Thread.sleep(2000);

        sensorTriggerPin.high(); // Make trigger pin HIGH

        Thread.sleep((long) 0.01);// Delay for 10 microseconds

        sensorTriggerPin.low(); // Make trigger pin LOW



        // Wait until the ECHO pin gets HIGH

        while (sensorEchoPin.isLow()) {



        }

        // Store the current time to calculate ECHO pin HIGH time.

        long startTime = System.nanoTime();

        // Wait until the ECHO pin gets LOW

        while (sensorEchoPin.isHigh()) {



        }

        // Store the echo pin HIGH end time to calculate ECHO pin HIGH time.

        long endTime = System.nanoTime();



        distanceCM = ((((endTime - startTime) / 1e3) / 2) / 29.1);

        // Printing out the distance in centimeters

        // System.out.println("Distance: " + distanceCM + " centimeters");



        return distanceCM;

    } catch (InterruptedException e) {

        e.printStackTrace();

    }

    return distanceCM;

}

}

You can use TStream.split() to create two streams: one whose tuples match your filter predicate and one for those that don't. You can then do whatever you want with either stream. e.g. TStream.peek(t -> System.out.println("excluded: " + t)), or TStream.print(...)

I implemented like this:

UltrasonicStream sensor = new UltrasonicStream();



DirectProvider dp = new DirectProvider();



Topology topology = dp.newTopology();



TStream<Double> tempReadings = topology.poll(sensor, 3, TimeUnit.SECONDS);



TStream<Double> filteredReadings = tempReadings.filter(reading -> {

    boolean threshold = reading < 20 || reading > 80;

    if (!threshold) {

        System.out.println(String.format("Threshold reached: %s cm", reading));

    }

    return threshold;

});

filteredReadings.print();



dp.submit(topology);