Anyone here na gumamit na ng RGB LED/White LED for color detection

[parengjomar07]

just want to ask your opinion about using RGB LED for color detection coz we're planning to use it for peso bill value detection. May nagsabi po kasi sakin na di sya effective kung sa pera gagamitin kea hingi sana ko ng second opinion. at kung di xa effective, anu pde naming alternative for value detection. salamat ng madami..GODbless you all

[Hero999]

Only the first and last sentence make sense, the rest is gibberish.

The easiest way is to use three LEDs: red green and blue, and a photo diode.

I'll post more information if you're interested.

[parengjomar07]

sorry for the late reply..kinda busy because its our finals week...well anyway. we are planning to use the whiteled and a photodiode for value detection of peso bills since each bills have their unique color. but one of our friend told us that using white led for color detection in peso bills is not effective since the colors used in our money is very light making it difficult for the receiver to distinguish the difference between each bills... and btw, are you a filipino also? thanks hero999 Godbless

[Hero999]

Great, it's good that you've returned. I didn't make much effort to respond in case you didn't return: many people don't.

English is the main language spoken on this forum. I'm from England myself but there are plenty of people here from all around the world.

I know there is a Filipino forum similar to this and I think some posters confuse this forum with it.

You could use three photo diodes with red, green and blue filters on them and a single white LED but it's probably better to use three LEDs and one photo diode. The idea, is you flash each LED on briefly at a high frequency and monitor the reflected light with the photo diode. You can sense the colour by monitoring the amount or red, green and blue reflected. Photo diodes tend to be more sensitive to longer wavelengths (i.e they're better at detecting red than blue) so you'll need to compensate for that whether by using software or making the green and blue LEDs brighter than the red LED.

You can buy LEDs with red, green and blue LEDs in the same package which will save space and maybe even money.

[parengjomar07]

your right about the filipino forum..lol. hmm.. is this kind of set-up using 3 LEDS and a photodiode enough to detect light colors?coz my friend told me that there is a problem in using the RGB for detecting light colors. Is there any way to compensate that problem?

[Alex Tsekenis]

I have come across some integrated colour detectors, 3 photodiodes with a colour filter. I have never used them so I can't comment further. Here are some:

http://au.farnell.com/jsp/search/browse.jsp?N=500001+1002850&Ntk=gensearch_001&Ntt=colour&Ntx=mode+matchallpartial

They are very expensive so maybe you could copy the technology using discreet photodiodes and colour filters. You will need to calibrate the set-up as the sensitivity to each colour will be different.

Sorry for using the Aussie site, UK one was unavailable.

[Hero999]

your right about the filipino forum..lol. hmm.. is this kind of set-up using 3 LEDS and a photodiode enough to detect light colors?coz my friend told me that there is a problem in using the RGB for detecting light colors. Is there any way to compensate that problem?

What problem would that be?

The only problem I'm aware of is the spectral response of the detector and I've already said how to fix it.

From a functional point of view it doesn't matter whether you use three detectors and one LED or three LEDs and one detector, both are equal. My colour scanner uses a monochrome image sensor and three LEDs strobed because it's cheaper than using a white LED and a colour sensor. The light appears white but you can see a rainbow effect at the edge of the lamp as it moves down the page.

If your using a microcontroller then it's probably easier to use three LEDs because the whole thing can be interfaced with using just three I/O pins but you can't turn all the LEDs off.