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Distance Sensor #4079 not working with 3.3 Volt Input

Sensor will not work with 3.3 volt input supply, only with 5.0 volts.


I moved your post to our sensors support category since it is a better setting for troubleshooting.

Can you post some pictures of your setup that show all of your connections and explain more about how you are powering and reading the sensor?

- Patrick

I’m using the Arduino IDE with serial monitor. Power is supplied from my PC via USB with 5.1 volts going to the Moteino R4. The sensor works as expected while it is powered from the VIN pin of the Moteino, which is 5.1 volts and the red LED changes intensity as measured distance changes. If I power the sensor from the Moteino on board 3.3 volt regulator (pin of the Moteino next to VIN) it does nothing and red LED stays off. The sensor output pin is connected to D6 of the Moteino which is PWM. I get the same results from two of the Pololu 4079 sensors.

IMG_1439 (2)

IMG_1440 (2)

Can you try measuring the voltage across the sensor’s VIN and GND pins to confirm that it is actually receiving power?

- Patrick

Yes, the sensor VIN and GND measures 3.29 VDC

We have tested that board with voltages as low as 3V, and we are not really sure how it could fail in a way that lets it work at 5V but not at 3.3V. That makes it especially strange that you are seeing this behavior from two units. Can you try measuring the on-board regulator voltage when the board is powered from both 5V and 3.3V? You can do that by touching one of these points with your positive multimeter lead and GND with the negative lead.

If you have an oscilloscope, could you use that to look at what is going as well? Specifically, please check for unusual noise or transients on the supply voltage and the regulator voltage.

Also, I suggest making sure your GND wire is seated securely in the breadboard. In your picture it looks like the it might not be making good contact (though it might just be a long pin instead).

- Patrick

I switched to a new breadboard and new jumpers.
With an input voltage of 5.10, the measured voltage on the test point you identified is 2.86.
With an input voltage of 3.29, the measured voltage on the test point you identified is 0.16.

I don’t currently have access to an oscilloscope.
Short of a defective regulator, I’m at a loss for why I’m seeing this behavior.

I truly do appreciate you working to resolve this issue.


It is starting to appear like there might be something wrong with the regulator on your board. Can you email us at support@pololu.com with your order information and a reference to this thread? Also, can you let us know if you got the same results with both boards?

- Patrick

I do get the same results from both of the sensors. I actually purchased 3 of the 4079 sensors when they were introduced. I just connected the 3rd one and I get same results as the other two. All three produce the same distance reading when connected to 5 volt supply and are quite accurate. I really like these sensors, just need them to operate at 3.3 volts.

I will contact support as suggested.

Thank you Patrick