FC-51 IR Proximity Sensor - am I doing it wrong?

So, I picked up a couple of these cheap-o IR knockoff FC-51 proximity sensor units off eBay. These things:


Simple as can be, you give it power, ground, and then the LM393 will give you either a 1 or a 0 on the output pin depending on the proximity of an object to the IR. You can adjust the sensitivity of the LM393 via the potentiometer. You can connect it to your Arduino and use the Serial monitor to check the state of the input pin, or you can hook up an LED and program it to light up when the sensor flips on, etc. But none of that is strictly necessary, because the unit comes with its own LED that tells you when you've tripped the sensor.

My problem is that I don't get more than a couple inches worth of sensitivity distance, max, no matter what I do. If I turn the potentiometer all the way clockwise (increase sensitivity), the sensor stays 100% tripped all the time. If I turn it back counter-clockwise a tiny bit, I can get the sensor to detect my hand when its about an inch or two away. If I go too far counter-clockwise, the sensor stops working altogether. I've tried 3v, 5v, lights in the house on, lights in the house off - no bueno.

The product advertises 80 cm of sensitivity, and even if that's a stretch, there are reviews online where people claim to have gotten at least 30 cm sensitivity. Am I doing something wrong that I can't even get 10 cm sensitivity?

Usually ultrasonic sensors are used for obstacle avoidance, which measure the travel time of a pulse (ping) and thus can report the distance of the obstacle. The speed of light is too high for such a measurement, so the a (cheap) IR sensors only can detect the level of a reflection. The sensitivity will vary with the shape and IR characteristics of every single obstacle.

To Quote the ebay site Description.


  1. When the module detects an obstacle in front of the signal , the green indicator light on the board level , while low-level continuous output signal OUT port , the module detects the distance 2 ~ 30cm, detection angle 35 °, the distance can detect potential is adjusted clockwise adjustment potentiometer to detect the distance increases ; counterclockwise to adjust the potentiometer to reduce the detection distance .

I see 30cm quoted.
The type of surface of the object will possibly have an effect to, especially if it absorbs IR energy.
Tom.. :slight_smile:

same problem,,,dint find a answer....hope to find soon !

I have the same problem. I bought about forty. Most have a range of almost ten centimeters. A few have a longer range but only about 20cm max. I've tried putting a divider between the ir transmitter and receiver in case it was picking up too much light from the led being right next to the receiver but nothing helps. I think the people claiming thirty centimeter might be liars.

Its maybe a very late reply but I had this same issue.
After playing around wit the FC-51 board I found a possible solution.
When i had taken a look at the two leds on the board I tried to re-aline them a bit.
The two leds are very sensitive.

My first distance i could calibrate was maximum 10cm.
I first turned the potential meter clockwise to almost trigger the constantly flasing green led. (maximum distance)
When I then straightend the two leds it got worse. No communication between the leds.
Then when I pushed the two leds to eachother the distance went to more then 35 cm but very unstable.
When i finally got the right setup around 30cm i then finetuned it with the potentiol meter to 20cm.
20cm is the distance I needed for my project.
So solution is laying in the alignement of the IR leds bulbs!!!

The surface where the board or leds are laying on is very important too.
Like having the board in the air or laying on a peace of cardboard.
I want to install only the leds on a sink so I will need to check if there are any issues there because i will remove the leds from the PCB board and solder it to extented wires.

Ik hope this can help other people who also find issues with the FC-51

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