The Way of finding the right Sonar Sensor

Different Sonar senors (sound navigation and ranging) were tested in additon to the development of the boat. The original goal was to achieve a stable and cost-effective detection of the aquatic bed or river bed morphologie. Sonar systems allow a distance determination based on emitted sound pulses. During the project, four active sonars were tested, which themselves emit signals and receive echoes in order to determine the distance based on the runtime. Tests were carried out on land as well as in various areas of the Lahn river.

Raspberry Pi Distance Sensor HC-SR04

Image 1 HC-SR04 (from tutorials-raspberrypi.de)

The ultrasonic module HC-SR04 was the first attempt to find a suitable sensor. According to the producer, the module is suitable for distance measurements between two centimetres and a maximum of three metres. The opening angle of the transmitter is 15°. The sensor requires a supply voltage of +5 volts and can easily be connected to a Raspberry via four pins.

Price: around 2 Euro

Examples for hardware setup and code examples:

https://pimylifeup.com/raspberry-pi-distance-sensor/

https://www.youtube.com/watch?v=xACy8l3LsXI

https://tutorials-raspberrypi.de/entfernung-messen-mit-ultraschallsensor-hc-sr04/ (German)

Although the HC-SR04 provides good measurement results, the main problem was to make the sensor waterproof. While there were considerations to dip the sensor in silicone and provide it with a mobile phone protection film in front of the sensor system, this has not been tested until now.For our tests we used the following script from https://tutorials-raspberrypi.de/entfernung-messen-mit-ultraschallsensor-hc-sr04/, with the modification “distanz = (TimeElapsed * 34300) / 2” to simulate the runtime for a measurement under water:

#Bibliotheken einbinden
import RPi.GPIO as GPIO
import time
 
#GPIO Modus (BOARD / BCM)
GPIO.setmode(GPIO.BCM)
 
#GPIO Pins zuweisen
GPIO_TRIGGER = 18
GPIO_ECHO = 24
 
#Richtung der GPIO-Pins festlegen (IN / OUT)
GPIO.setup(GPIO_TRIGGER, GPIO.OUT)
GPIO.setup(GPIO_ECHO, GPIO.IN)
 
def distanz():
    # setze Trigger auf HIGH
    GPIO.output(GPIO_TRIGGER, True)
 
    # setze Trigger nach 0.01ms aus LOW
    time.sleep(0.00001)
    GPIO.output(GPIO_TRIGGER, False)
 
    StartZeit = time.time()
    StopZeit = time.time()
 
    # speichere Startzeit
    while GPIO.input(GPIO_ECHO) == 0:
        StartZeit = time.time()
 
    # speichere Ankunftszeit
    while GPIO.input(GPIO_ECHO) == 1:
        StopZeit = time.time()
 
    # Zeit Differenz zwischen Start und Ankunft
    TimeElapsed = StopZeit - StartZeit
    # mit der Schallgeschwindigkeit (34300 cm/s) multiplizieren
    # und durch 2 teilen, da hin und zurueck
    distanz = (TimeElapsed * 34300) / 2
 
    return distanz
 
if __name__ == '__main__':
    try:
        while True:
            abstand = distanz()
            print ("Gemessene Entfernung = %.1f cm" % abstand)
            time.sleep(1)
 
        # Beim Abbruch durch STRG+C resetten
    except KeyboardInterrupt:
        print("Messung vom User gestoppt")
        GPIO.cleanup()      

Waterproof Ultrasonic Distance Measuring Module

Image 2 JSN-SR04T (from raspberrypi-spy.co.uk)

After the first tests with the HR-SR04 module and water resistance problems, the JSN-SR04T “Waterproof Ultrasonic Distance Measuring Module” was chosen. The module also requires +5V as power supply. Measurement distances is accurate about 0.5 cm and the maximum distance is 4.5 meters.

After the first successful tests in the dry, using the same script as the HR-SR04, we had to determine that the watertightness of the ultrasonic sensor only refers to the probe, i.e. it can be used in rain and not under water. In that time, it was also difficult to attach the sonor to the body of the boat in order to achieve a good vertical depth measurement in the water.

Price: around 18 Euro

Examples for hardware setup and code examples:

https://www.raspberrypi-spy.co.uk/2016/10/waterproof-ultrasonic-distance-measuring-module/#prettyPhoto

Advisement on MB7354 HRXL-MaxSonar-WRS5

Image 3 MB7354 (from maxbotix.com)

The MB7354 “HRXL-MaxSonar-WRS5” was selected as the third test module. One reason for the selection was the weather resistance described by the manufacturer and the robust PVC housing. Actually intended for measuring snow depths, the module is equipped with an internal filter and a temperature sensor. The resolution of the sensor is specified as 1 mm at a maximum range of 5m. As the use under water is not recommended, this sensor was not tested.

Price: 40 $

Further informations and product specifications:

https://www.maxbotix.com/Ultrasonic_Sensors/MB7354.htm

https://www.maxbotix.com/documents/HRXL-MaxSonar-WRS_Datasheet.pdf

Final Selection: Deeper Samrt Sonar Pro+