Pololu 38 kHz IR Proximity Sensor output always LOW

I am using the Pololu 38 kHz IR Proximity Sensor (uses Vishay’s TSSP77038 Modulated IR Tx-Rx).

The problem is, the sensor always seems to output a LOW (0V), irrespective of whether or not there is any obstacle in front of it. A LOW output indicates that there is an obstacle in front of the sensor (active low).

My Circuit:
Barebones circuit- ENABLE pin disconnected, Output pin connected to the positive lead of a multimeter. Vin at 5V and GND at 0V. On a breadboard.

Testing process:

  • Kept the sensor clear of all obstacles (there is nothing in front of the sensor for about 10m). Sensor Output is LOW.
  • Introduced an obstacle quit close to the sensor (about 5cm). Sensor still reads LOW.
  • Changed the sensor module (Tried 5 different sensor modules), same observations.
  • Tried rotating the potentiometer to see if the problem has anything to do with the range. Tried the entire range of the potentiometer, no effect.

Am I doing something wrong?



Could you please post a picture of your setup including all connections. Also, what lighting is in the area you are testing? Some types of florescent lighting (or sunlight) put out light in the 38kHz range; could you try testing them in a dark room (e.g. with the lights off and far away from any sunlight)?


Hi Derrill,

I have the simple setup shown in the image above. The lighting is minimal in the room that I was testing. There is only one CFL (white) in the room. In fact, I even switched off the lights completely and made the room dark (I was testing at night) to see if the ambient light was causing issues. I don’t think it is because of ambient light interference.

Just to test that theory out, I took the sensor out in the middle of the night (no streetlights also) and tested it out there, but the sensor output continues to remain low.

Also, I tested with Vdd = 3.3V, but the result is still the same.

Is the image above the suggested setup for the sensor module?

Is there a way to check if the sensor is faulty? Although I hardly doubt that this is the case, because I tried out with 5 different sensor modules.


Could you please post a picture of your actual setup that includes all of your connections?


Here is a photo og my setup. Sorry for the poor lighting:

Here is a close-up:

The 2 probes are connected to the multimeter, and measure the voltage across the Output and GND terminals of the sensor. The arduino is just being used as the 5V supply. No connections have been made except for Vdd and GND.

The voltage measured with respect to GND at the terminals of the sensor are:
@VDD = 5V
@Output = 0V (always).

Both the red and green LEDs are ON on the sensor. If I am not wrong, this means that the IR LED is transmitting (as indicated by the Green LED) and the Sensor is detecting an obstacle (the Red LED). But that is not the case, as I have observed in a dark, empty room.

The “limitations” section of the sensor’s product page cautions that the sensor has a wide sensing angle, which can cause it to be triggered by proximity to parallel objects, such a the floor. Could you please set your sensor setup at the edge of a table so it is off the floor? Also, you might try moving the sensor so it sticks out past the edge of the breadboard.


I was actually testing it like you suggested (sensor at a height, off the edge).

The photograph was taken with the setup on the floor.

I will try having the sensor away from the breadboard today.

The setup that I have is correct, is it not?


Hi Derrill,
I tried what you suggested, but it did not seem to affect the outcome. The sensor continues to give a LOW output.

Yes, your setup looks fine. Could you try disabling the IR LED and tell me how that affects your reading?


By making the ENABLE pin LOW?

Yes, by driving the ENABLE pin LOW.


I tried that last night. When I drive the ENABLE pin LOW, both the RED and the GREEN LEDs turn off.

That makes it seem pretty conclusive that the sensor is seeing itself (as opposed to picking up ambient IR). Given that we test all our boards before we ship them, we have not had anyone else report problems like this, and all of your boards are suffering from the same problem, I very strongly suspect you are doing something wrong, but at this point I cannot determine what that is. Would it be possible for you to post a video demonstration of the problem and an in-focus, high-resolution picture of both sides of your sensor PCB (if your camera has a macro mode, it could help to use that)?


I just got one of these sensors and I’m having the exact same problem. The only difference in my setup and the one of the OP is that I’m powering the sensor via an LM7805 chip that is fed by a 9v battery. I also used the angled headers instead of the straight so my sensor is pointing straight up. I turned off all of the lights in the room at night and the RED LED stayed on constantly. I do not have any other sensor modules to test if this one is bad, but I’m going to check the thing about tying the ENABLE pin to low and see what happens. If so, then I think I’m going to try to do some optical shielding around the reciever.

Connecting the ENABLE pin to LOW does turn off both LEDs. The optical shielding didn’t work either. I basically cut a 1/2 inch long piece of shrink tubing and stuck it around the receiver. Something has to be wrong because there’s no way this thing should be that sensitive.

Ok I finally got this thing working in case anyone else wants to know what it takes. What I found is that the receiver is stupidly SENSITIVE! I put a 1 k pot in series with the supply voltage and turned it as far as it would go which killed the green LED completely, but the red LED was still faintly shining. But when I backed off from the breadboard it went off! With no optical isolation, the red LED would come on if i got within 2 inches of the sensor from ANY direction. With my first attempt at optical isolation installed (just a 1/2 inch piece of 3/8 in dia. shrink tubing stuck around the receiver), the sensing was limited to directly above the sensor as hoped for, but since the back of the sensor was open, it would also turn on if i put my finger between it and the breadboard.

So my final working setup is this:
I found a smaller diameter piece of shrink tubing that barely fit around the receiver. I cut it also about 3/8 to 1/2 inch long and pressed it around the receiver. Then I cut a piece of electrical tape about 2 inches long by 1/4 inch wide and wrapped it around the end of the board with the emitter and receiver, careful not to cover up the emitting side of the emitter but also covered the rest of the receiver that was not already covered by the shrink tubing. Now I can turn the 1k pot to practically zero and the output still does not come on until my hand is within 6.5 inches above the sensor. I have not tried to tune the 555 timer via the onboard pot, but I can decrease sensing range by increasing the 1k pot I used.

I’ll post pictures later if I get a chance. All in all, this seems like a lot of rigging just to get this sensor to work at all, much less as described on the product page.

Hi, DMC045.

I’m glad you have the sensor working better now. Sorry to hear that it was a troublesome experience for you. Did you feel that the product description was misleading? (We do have some warnings on the product page that the sensing angle is wide, which leads to the possibility of side reflections triggering the sensor, and that shielding might be necessary.)

Here are a few more suggestions that might help anyone else having problems with excessive sensitivity:

  • If you detune the emitter frequency with the onboard potentiometer, it should decrease the sensor’s sensitivity (in all directions: both in the forward direction and from surrounding reflections).

  • If you don’t need the full range of the high brightness sensor, switching to the low brightness version might help avoid unwanted reflections.

  • It is much easier to apply shielding and control directionality with two separate sensor boards, using one to transmit only (ignoring its OUT pin) and the other to receive only (tying ENABLE low to turn off the emitter).

- Kevin

I too am seeing the same issue. With the sensor pointed to the ceiling more than 2 meters away the sensor output is low. I’ve tried completely blocking the receiver and the output remains the same. Only by pulling the enable line low am I able to turn off the red light (and green light).

Sorry, didn’t see the additional replies. Got mine working by using a variable power supply and dropping the voltage closer to 3.3VDC. After some playing with the pot, it works on 5VDC too.


Thank you for letting us know you got it working.