Sensing Error

[Tom]

My Ultrasonic sensor program will only return a distance of 4 inches or less.  I have been unable to determine the cause.  I have set it up if different environments to make sure that is was not getting so odd reflection.

[011235813]

Can you post the code?

[Tom]

I used the code that I downloaded from this site for ultrasonic test. So, you can take a look on line.

[jasea]

Hi Tom, There are two code samples on the download site, which are you using, and have you made ANY changes to it? Also can you confirm that you have connected the Ultrasonic Sensor correctly:
Pin VCC to +5V,
Trig to Stem pin Digital 2
Echo to Stem pin Digital 4
Gnd to Stem Gnd.

When you say that the sensor only returns a distance of 4 inches or less, do you mean that it only detects an obstruction that is 4 inches or less away, or it returns a distance of 4 inches irrespective of how far away the object is.

[Tom]

I used the sample titled Ultrasonic sensor test. I verified the leads for the sensor and they are correct. The sensor returns a maximum of 4 inches even if it is pointed at a wall 10 ft. away. I put a finger directly over the sensor and it returns an extremely high number as described in the directions. It appears to be functional but there something in the software calculation.

[jasea]

Hi again Tom, one more item to check, is the power switch on the STEM Board in the 5V position? if not then place it to this position and try your testing again.
If it is, are you confident to change the code for the program "Ultrasonic sensor test " in the Arduino IDE?
If so then change the last line in the void loop() function
from
delay(10);
to
delay(1000);
This will slowdown the output to the terminal window to once a second.

Now you will need something flat and solid to reflect the ultrasound back to the receiver, I use a small wooden box.
Whilst running the changed program and watching the terminal window move your object slowly away from the sensor.
mine goes
1212in, 3092cm
1in, 3 cm at a distance of about ⅓ inch to 1 inch
2in, 5 cm at a distance of 5 CM

The accuracy is good at 10, 15 , 20, 25 and 30 CM

what do you get from your sensor?

[Tom]

When I place the reflector against the sensor the reading is 1226 inches and when I move the reflector away from the sensor it will display 1,then 2, then 3, and then 4 and nothing above 4 even at 2 feet.

[jasea]

Hi Tom, Well I have had a look on the Web, but I can find no problems with the HC-SR04 like you describe. These devices either work or they don't. So assuming that it is not damaged, has been correctly installed in the bracket, then I guess that the sensor is faulty.
One last test, try adding the following two lines of code after the line " duration = pulseIn(echoPin, HIGH); " in the ping() routine. This will print on the delay in microsecond between sending the pulse and receiving it back.

Serial.print("duration = ");
Serial.println(duration);

I suspect that you will see a similar result to that when it is converted to inches, but this will eliminate the calculations from the problem, and confirm that the sensor is faulty. You can get them from most of the hardware shops and online at Amazon.

Do let us know what you find

[Tom]

I inserted the lines and the duration displayed would go no higher than 619 with a distance of 4 inches. I am now sure it is the sensor so I will go look for a replacement.
Thanks.

[Mel]

Thanks, jasea for helping out with all the right checks!!

@tom, email us at [e-mail] and we can help you out with that replacement.

Thanks!
Melissa

[Tom]

I got a replacement and installed it yesterday. Everything works perfectly now. The new sensor was a slightly different size but it fit and works. Thanks for all the help.

[jasea]

Hi Tom, Thank you for letting us know that you have solved your problem. Now you can start having FUN!

[howie]

Glad to have found this. Mine was doing 2 inches (rarely 3). Found the exact same sensor on ebay for $0.99. Got 2.

Microcenter wanted $30.

[jasea]

Hi howie,
Please let us know if the new sensor fixes your problem.

Regards

John

[howie]

Yep. New sensor worked great. Ebay is a great place for cheap parts.