Errors in distance measurements with the LV-MaxSonar EZ serie

Other Hardware Sensors
1

I am working with the LV-MaxSonar EZ2 and a Raspberry Pi 3 model B. As you know, The Raspberry Pi can not read analog input, that's why I used an ADC (analog to digital converter), an MCP3008 to convert the analog-volt to a digital input for the the raspberry. I followed this tutorial : [u]https://github.com/alx-s/RPi_tutorials/tree/master/Analog_inputs-MaxBotix[/u]

Except that I wired the VREF pin of the MCP3008 to the 3.3V pin of the raspberry (because I tried with the 5V pin, but it didn't work).

After running the script, I got a logical output. However, there was an error rate that grows with the distance between the sensor and the object. The following examples explain that :

An object that is 16 cm away from the sensor ----> the output is 21 cm
An object that is 17 cm away from the sensor ----> the output is 21 cm
An object that is 18 cm away from the sensor ----> the output is 21 cm
An object that is 19 cm away from the sensor ----> the output is 24 cm
An object that is 35 cm away from the sensor ----> the output is 42 cm
An object that is 56 cm away from the sensor ----> the output is 66 cm & 67cm
An object that is 70 cm away from the sensor ----> the output is 84 cm
An object that is 84 cm away from the sensor ----> the output is 96 cm

Since I got these errors, I decided to try Arduino.
At first, I used an Arduino Nano, and followed the tutorial in published by Maxbotix in their website , link : [u]https://www.maxbotix.com/Arduino-Ultrasonic-Sensors-085/[/u]

Since the Arduino Nano does not contain Pwm pins, I used the Analog-Volt code for a single sensor from the same website (Maxbotix website) and I followed the whole tutorial. The results that I got were closer than with the Raspberry Pi, but they were not precise:

An object that is 30 cm away from the sensors ----> the output is 27.84 cm
An object that is 25 cm away from the sensors ----> the output is 22.94 cm

Since the results were not precise, I decided to use an Arduino Uno this time. I used both the Pwm and the Analog-Volt and I got the same error rate as with the Arduino Nano.

I even tried different sensors, but I got the same errors.

So please, If you have any advices or recommendations about this problem, please mention them. Thank you.

2

Have you read the datasheet? Useful things them are.
e.g.

Sensor Operation from 6-inches to 20-inches
Because of acoustic phase effects in the near field, objects between 6-inches and 20-inches may experience acoustic phase cancellation of the returning waveform resulting in inaccuracies of up to 2-inches. These effects become less prevalent as the target distance increases, and has not been observed past 20-inches.

Pete

3

What sort of accuracy were you expecting with this? The datasheet specifies a resolution of one inch but I can't find anything about accuracy.

Pete

4

I checked the datasheet, according to what was written, there is no problem with the measurements taken with the Arduino. However the measurements taken by the Raspberry, are completely wrong.

5

Haven't you solved your own problem? Use a Nano or UNO.
If you want an explanation of the poor performance of the Rpi, you're more likely to get informed answers on an RPi forum.

Pete

6

The problem of the Arduino is solved. :grinning:
I only put the part that talks about the RPi to give more details, I was not expecting to get a solution about the problem related to the RPi here.
Thank you for your help :slight_smile: