How to recognize the color of a led ?

[Externet]

Hi fellows.
To create some automation, it would be needed to discern which single of several different colored leds behind a translucent button is lit.
How to tell with some photosensors which color is shown? Different optical filters over several sensors? Are there phototransistors/photodiodes that sharply respond only to a single color? Wave lenght recognition? Suggestions ?
Miguel

[rshayes]

You can detect color by using several photodetectors with different filters in front of them. Ideally, you could use two sensors, one with a filter that peaks in the blue region and tapers off gradually toward the red and the other with a filter that peaks in the red and tapers off gradually toward the blue. The difference of the two signals divided by their sum would be independent of amplitude and characteristic for each color.

Another approach would be multiple detectors with different but overlapping filters. These signals can be weighted and added together, with one set of weighting factors for each diode wavelength. The highest weighted sum will indicate which color of LED is illuminated.

<small>[ March 17, 2006, 02:06 PM: Message edited by: stephen ]</small>

[cato]

didn't someone post a link to an M&M sorting robot here a year or so ago? There must have been a color sensor in that thing....

[cato]

Damn.... I've got a mind like a steal trap....

http://www.parallax.com/detail.asp?product_id=30054

now if I could only remember where I set the remote 3 minutes ago....

[Externet]

Good information, cato!
Thank you still have a mind
Miguel

[Chris Smith]

If you have control over the LEDS them self, frequency code each one differently, using a 555.

That way they may appear simply colored to you, and pulse coded to the machinery reading them using a 567.

[Sambuchi]

Heres something I think may help you... and if you have some spare time look around his site... its great!!!!!!!!

http://www.robotroom.com/ColorSensor.html

Good Luck