QTR-1A alternative not susceptible to ambient light


finished a project using the QTR-1A reflectance sensor as a proximity sensor. everything works but the distance to trigger it varies depending on the ambient light. Its affected by IR in the ambient light and thats messing up the distance from when its supposed to trigger. I have to keep readjusting the distance according to how much ambient light there is.

I need the distance for it to trigger, about 3-5mm but it has to reliably trigger at the set distance and not be affected by ambient light.

are there any sensors i can replace the QTR-1A with that is not affected by ambient light that can be used as a proximity sensor?

thanks for you help.



Our Sharp digital distance sensors are mostly immune to ambient light, but the shortest-range version we have has a minimum detection distance of 5mm, so I’m not sure if it would be suitable for your application.

For very short range proximity detection, I think the QTR sensors are still your best bet. Can you shield it from ambient light?

- Ben

hi Ben,

thanks for the reply.

5mm will work, i just have to adjust the distance of the sensor to the moving object its detecting. its a fixed distance. when the object comes within range, it should trigger the sensor.

i could try shielding the QTR, but as it stands, its even affected by sunlight coming in from a the window… and thats not much. I wonder if making a funnel/shroud will help.i dont feel its an elegant solution to the problem.

if the sharp sensor is immune to ambient light IR, i may give it a try.

i came across this sensor over at sparkfun, Optical Detector / Phototransistor - QRD1114
link to data sheet: sparkfun.com/datasheets/BOT/QRD1114.pdf

it claims to have a daylight filter on it… would that mean its immune to ambient light IR?

looking forward to your reply.


Those QRD1114 sensors are the ones we initially used on our QTR sensors and they are very similar to the versions we currently use. They are both affected by the IR in ambient light. Sunlight has quite a bit of IR, so if you can’t shield the sensor from this, I suggest you use a digital distance sensor such as the Sharp model I linked in my previous post.

- Ben

Thanks for you reply Ben.

will try out the Sharp sensor and hope it fits the bill.

will report how it goes.


Hi Ben,

went through the specs of the Sharp sensor and it states that its “digital” with only two states, output low and high.
would this work with the pololu maestro 6 controllers input which is analog?

can the maestro 6 detect the sharp sensors output as low or high and use it to trigger a servo?

i dont need ranging, just a yes or no proximity sensor to trip a servo to a preset position.

(sorry, i failed to mention this in my first post, but the QRT sensor for my project was used with a Maestro 6 and a rc servo.)

EDIT: may have answered my own question. stumbled across its use in the hexapod robot while looking around for an answer.


I’ve ordered up the parts i need. (after discovering it would work.)

ive got another question… would a modulated IR sensor (eg IS471) be more resistant to ambient light IR compared to the sharp sensor?

something for me to keep in mind as an alternative.

looking forward to your reply,


The Sharp distance sensors are nearly immune to ambient IR, so I don’t think you’ll need to worry about finding a more noise-resistant solution. Alternatives are good to keep in mind (yes, modulating IR is a good way to make a system resistant to interference from ambient IR), but I suggest you try the Sharp sensor first and see how it works before spending too much time thinking about other options.

- Ben


thanks for your reply and insight.
its much appreciated Ben.
will report as to how it turns out.


I am using a fairly old Sharp Distance Measurement sensor I had around, not using the new ones from Sharp. not sure the difference…
PartNumber I am using is GP2D12 F 69, and they work similar… I guess.

So I have my own robot built using 3 of them, and all works fine indoors… I just got scared when I took it outside… (Actually only garage door was opened) and my autonomous vehicle got wild… just because sensor got some daylight…

Do you mean Sharp Sensors are REALLY immune to daylight? It was not direct sun light for sure…

The Sharp sensors are not robust in sunlight, because the sunlight totally washes out the emitted IR from the sensor.
The sensors are robust against “indoors type” IR ambient variations because they detect the modulated IR that they emit. They can’t do that outdoors because of the strong saturation of sunlight.

OK, that was my guess… so basically sensors I have are OK.

I am trying to get a low cost camera sensor connected to arduino and a laser pointer with angle, and based on position of laser on camera image we have our distance.

Basically same as Sharp but using visible laser pointer. This would work on daylight. Not so fast but I would say immune to noise… and sharp target.

Now I only need to understand a good camera source with serial interface to get RGB info, so that I remove ambient with image subtraction of 2 frames. One off laser one on laser…

While there exists a few, expensive-ish, cameras with serial I/O, an Arduino isn’t really up to the task of the kind of visual processing you need to make that solution robust. I’d suggest using a Raspberry Pi, and perhaps the camera module that comes with it.

Also, lasers stronger than some limit (1 mW?) are dangerous when pointed at eyes, so trying to build a LIDAR-like distance sensor like you suggest with good daylight visibility may be hazardous to the surrounding people. It’s a real PITA!