Why the three holes of the NXT2 color sensor?

[mindsqualls]

When looking at the NXT2 color sensor front on, it has three holes that open up to either a light-emitter or a sensor.

The top-right one has three diodes inside: red, green and blue.

The top-left seems to be a sensor, and so does the bottom one. I base this assumption on a very primitive experiment; blinding one of them with a finger-tip, the color sensor as a whole still is able to do a color-reading.

But why the two sensors? Studying them closely they look different.

(For a while I even suspected that the bottom one wasn’t even a sensor but perhaps just a “bump” of opaque plastic, there for decorations or whatever.)

My guess is that they are sensitive at different areas of wavelength and that the color sensor tries to combine the reading of each of them for a more accurate value. Say, one of them sensitive in the red area and the other in the blue i.e. at the opposite ends of the visible spectrum.

[mightor]

I just took one of mine apart to look inside and I can assure you that there are only two sensors in there. One is the LED, another the receptor and the bottom hole is not really a hole at all and is just a small bump in the cover. I can only assume it's for decorative purposes, to make it more balanced, RGB, ergo three holes, that sort of thing.



I will post some additional pictures of the sensor's guts tomorrow on my blog, so you can see for yourself.

- Xander

[mindsqualls]

Ok, thanks. I guess that perhaps I must have slipped some light in past a fingernail or something like that.

So it turned out that my suspicion about the opaque bump of plastic was correct after all. Perhaps they just wanted it to look sufficiently different from the NXT1 light sensor.

Looking forward to those pictures. BTW how do you take it apart without damaging it?

[mightor]

Looking forward to those pictures. BTW how do you take it apart without damaging it?

Easy! I don't! I take a knife to the small sticky-outy bits on the white cover that stick into the grey part. Once the white cover is off, you need to press in three spots and it opens like a pistachio.

I have never succeeded in opening one of these without at least destroying the white cover. Lucky for me I have some spare covers

- Xander

[philoo]

I use the same method to open sensors. But whe I cut the white tabs I take care to leave a bit of them attached to the cover by holding the blade slanted. This is enough to hold the cover after reassembly.

[mightor]

Ah clever trick. I will use that from now on as well

The blog post is finished and scheduled for release in a few hours.

- Xander