Color Filter

pick up something like this

or this

and try various filters until you find one that works for you.

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Does this mean you have little faith in the Vision Sensor’s built-in ability to select colors? I’m not trying to be snarky - I don’t have access to the vision sensor yet - but I was hoping it could select colors without any physical filters.

Do you think layering yellow cellophane could work as a filter? It would be cheap and readily available.

It’s nothing to do with the vision sensor, OP asked about the light sensor. presumably this.

also, for more info on light sensor see this

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Oh, heck, I’ve got Vision Sensor on the brain.

Okay, in that case, maybe the OP might also consider using the Line Follower. If I recall correctly, some kids played with the Line Follower last year and found it could easily detect the difference between the red and blue floor goals, and also the floor tiles. Since it has its own emitter, it might work better than the Light Sensor, which depends on ambient lighting. Of course, the Line Follower is “seeing” in infrared, so it might “see” the various plastics much differently than they look to the human eye.

What would be an acceptable way to attach the filter to the robot to comply with vex turning point competition rules?

Last season I had two light sensors right next to each other- one standard and one filtered with yellow tape- and compared the values given by the two to identify cones. It worked well (as long as the cone was right up against it of course). Because the tape absorbs most non-yellow light, the closer together the values of the two sensors are are, the closer the light is to the color of the filter. I don’t know the exact brand of tape I used (I’ve had it for years for electronics work), but here is a similar one.

As @FullMetalMentor said, line followers work well too, so if you have one of those lying around you can try that too (just remember that filtering the line tracker the way I described above is not at all practical, as they work in the infrared spectrum rather than visible light).

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Can the line tracker distinguish color in the visible light spectrum even though it uses infrared light?

I somewhat doubt it. If I’m not mistaken, that dark piece of plastic over its “window” is a filter that allows in mostly infrared light, the same wavelengths that its built-in IR LED emits.

Yeah I just tested the line tracker and it can’t distinguish between the different colors of the parking platforms. However, I also tested the light sensor and the yellow platform reflects significantly more light than the red and blue platforms which really helps what I need it for. I’m still gonna test the light sensor with a yellow filter just to get a bigger difference between the yellow platform and the other two platforms. I just haven’t gotten it yet.

Is it acceptable to tape the color filter straight onto the light sensor? I know tape is restricted in most cases but I don’t know how else to attach the filter to the light sensor.

I can’t provide an official answer, but I would say that your use of tape as a color filter definitely falls under the regulation that allows for the use of a color filter. Since the tape is used strictly as a color filter and is not holding other things in place, I think it qualifies. But that’s just my opinion:

<R7> Robots are allowed the following additional “non-VEX” components:
a. Any material strictly used as a color filter or a color marker for a VEX Light Sensor or Vision

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And that still works even though the tape is not the actual filter? It’s just holding the color filter in place.

In that case, I don’t think you would probably be within a super strict interpretation of the rules.

Is the filter a solid piece of plastic or is it like plastic wrapper material? Can you hold the filter in place with rubber bands or maybe make a holder/frrame for it with pieces of bar? There is adhesive on the back of the Vex foam material - could you stick it on with that?

Personally, if I were an inspector, I would probably allow tape in this case because I could consider it as being part of the filter, but you never know when you might get an inspector who’s very picky.

The filter is a piece of gel that I got from the theater department at my high school. It’s the clear colored plastic stuff that they use to cover the white stage lights to change their color. I tested it and it works really well. I layered a piece of amber gel on top of a piece of green gel and it filters out the red and blue platforms and only sees the yellow one.

That’s excellent! If it’s not stiff enough to make a little frame for it out of something lightweight like Vex bar can you perhaps sandwich it between two pieces of clear polycarbonate (which is a type allowed by the rules)?

Just be sure to test out your completed sensor under the same kinds of lighting conditions in which you’ll be running the robot. The Light Sensor is dependent on the lighting in the room, so if you shift from a room alit by daylight to, say, a gymnasium that is alit by electric lights, you might see a little difference. But, in general, I’m guessing your filtration will do the trick. It’s a great idea!

Ok and thank you so much. You have been extremely helpful. The clear polycarbonate is a really good idea that I never thought of. I’m going to try that out. We plan to mount the light sensor underneath the robot where it is darker. We will put a vex flashlight right next to it to reflect off the platform. That way we can minimize the ambient light interference in the sensor.

If you want an official answer to this question, you must post the question to the official Vex Q&A forum, which is found here:

I think you might need to have administrative access to your club’s account - or whatever it’s called - in order to post there, however. You might need to ask the person in charge of your club, if that’s not you. Also, be aware: I’m sorry to say it can take 1-3 weeks for the officials to give you an answer on the Q&A. Another option might be to google around to see if you can find an old official answer to your question and then print it out to use at competitions in case any inspectors get picky about it.

In any case, I don’t think posting the question in the “Official Tech Support” category of the regular Vex forum will necessarily give you an official answer.