Color Detection

[demestav]

Hello. I was wondering how a low budget color detection can be possible. I have seen in another threat that 3 LED (R,G,B) can be used and measure the intensity of light. But i have seen the LEGO MINDSTORM sensor that has only on LED (i think). I there such a component?

Thank you

 

[zachtheterrible]

There are single LEDs that has RGB in it, so that it is a multicolor LED.

 

[demestav]

Thank you zachtheterrible for your reply. So i guess mesasuring the reflection is the only solution? :?:

Thank you

 

[Dean Huster]

One solution I saw blasted a white LED at the sample and three filtered receivers measured the intensity. You had to put the standard sample under the detector and store the resulting readings as a "color". The simple system I saw was a demonstration for sorting m&ms into their various colors.

Dean

 

[zachtheterrible]

If three LEDs could do it, a single multicolor LED i would imagine could do it. It has four leads, one for red, one for green, and one for blue, and one for ground.

 

[demestav]

Thank you for your replies. I will try it out.

 

[demestav]

Hello. I back on this project and now i really need to find something simple and quick. The RGB LED would be well outside my budget. I think it should work with only one trans-receive IR module. However it would be great if someone could suggest a IR component to buy.

Thank you.

 

[audioguru]

A trans-receive IR module works with IR, which is infrared that has a frequency lower than visible light. It might pickup a small reflection from a red object, because the frequency of red is near the frequency of IR, but it wouldn't pickup an IR reflection from another colour.

 

[mechie]

Quick and Simple ?

I really need to find something simple and quick.

What kind of resolution are you after?
Are you trying to resolve shades of the same colour or just differentiate between, say, red, green and yellow?
What ambient lighting is there or is this a sensor that gets very close to (touches?) the object?

Would a simple torch bulb be OK for illumination and three LDRs, each with a colour filter (primaries or secondaries or "Quality Street" sweet wrappers) work as detectors?

 

[demestav]

What kind of resolution are you after?
Are you trying to resolve shades of the same colour or just differentiate between, say, red, green and yellow?

Well I want the most basic color resolution possible!!!! Let's just say to seperate black from white.

Lego mindstorms have a IR module which can distinguish varius color (i tried it) and has only one receiver and one transmitter.

Thank you for your quick replies...

 

[audioguru]

I want the most basic color resolution possible!!!! Let's just say to seperate black from white.

Do you want colors or do you want black and white? Pure white is easy to detect since it contains all colors including IR. A trans-receive IR module would be able to give high resolution to the amount of IR that is reflected by different white samples. A redish grey might give the same output as a greenish white.

Lego mindstorms have a IR module which can distinguish varius color (i tried it) and has only one receiver and one transmitter.

I couldn't fing a link to your LEGO color test, but found one where the LEGO IR was reflected off two LEGO bricks and the test was repeated using bricks of different colors. All colors including black (it was probably shiny) reflected some IR, red and yellow reflected the same amount and other colors a lesser amount. It could probably determine the LEGO bricks that reflected IR at different amounts from each other. **broken link removed**
It is not the same as color resolution.

 

[demestav]

Do you want colors or do you want black and white?

I just want to able to understand two different colors, what ever those colors are.

So what you are saying is that i will use a IR transmitter and the IR receiver indication will vary (enough to be detected) according to the color (black or white) of the object. I there any particular IR transceiver that you suggest me to use???

Thank you.

 

[audioguru]

Black and white are not colors. They are the absence of reflected light and the presence of reflected light. Since you are using only IR, your indication will have a few unknown color variables. A bright green or blue reflected color would give the same indication as a dim red reflected color, and many other color combinations would be the same.

I wouldn't use IR to detect colors, I would use an RGB LED or 3 separate ones, and 3 light detectors with color filters. With the correct choice of LED and filter colors I would have very good resolution of any color.

 

[lord loh.]

A few friends of mine use a light detecting resistor and an OP-AMP to detect colours.

According to them, the resistance of the LDR was dependent on the colour of light incident on it. They first cliberated the opamps for a few colours.

I do not believe that this shall be very accurate but defnitely low cost.

 

[demestav]

Thank you for your answers.

Since i have already oredered a IR tranceiver for distance measuring purposes, I will test it next week and i will let you know for the result.

Thanks again.

 

[skot123]

Probably too late to be of any use, but I am building an M&M sorter. I am using 3 LEDs 1 red, 1 blue, and 1 green and a photo-resistor

(My design is inspired by https://www.philohome.com/sensors/colorsensor.htm)

The three LEDs are connected to a pin on a PIC the photo resistor is connected to a 5V source and an ADC port.

I flash the LEDs and I get an ADC reading (actually I get a bunch of them and average)

Then I compare with sample values.

I am able to get almost 100% correct based on the 6 M&M colors.

(woo-hooo first post by me)

 

[mstechca]

that is interesting, but just with 1 LDR???

the only way I can see this circuit pull off is if each light ray has a different frequency (which I think each one does), and colour is determined by frequency.

 

[Nigel Goodwin]

that is interesting, but just with 1 LDR???

the only way I can see this circuit pull off is if each light ray has a different frequency (which I think each one does), and colour is determined by frequency.

Different colours of light ARE different frequencies, although it's not really relevent to the thread?.

What actually makes something look a particular colour depends on what colours are absorbed, and what are reflected, by the object - in this case, it's very easy to see that by switching the LED colours you will find some colours reflect more then others, and can decide which M&M it is.

 

[audioguru]

Hmmmm. Is there any difference (and does it matter) between something that reflects purple, which is both red and blue being reflected, and something that reflects violet, which has a frequency higher than red or blue?
Why do purple and violet objects look the same colour when they are completely different?

Shine a red LED then a blue LED on a purple object and an LDR will pickup about an equal amount of reflection from each. Our eyes would also.
Then shine the red and blue LEDs on a violet object and the LDR will pickup almost no reflection from the red and a small amount from the blue, and I think the same with our eyes.
Therefore shouldn't we be blind to violet like our sensor?

Maybe there is no such thing as a violet object.
Shine red and blue LEDs at the same time and you see purple or violet light. Then use a violet filter on a white light (not a "white" LED) and you also see purple or violet. How come?? :lol:

 

[Nigel Goodwin]

I'm not really sure what you're on about Audioguru?, purple and violet are just slightly different shades of the same colour.

The three primary colours are Red, Blue and Green, you can mix these to get all the visible colours you want (as the monitor you're watching does!) - purple and violet are just Red and Blue, perhaps in slightly different ratios?.

Visible coloured surfaces (paint etc.) work differently though, Red, Blue and Green are the primary colours for LIGHT - this is an addative process, paint is a subtractive process, so the primary colours are different.

So your coloured suface (purple or violet) doesn't 'reflect' purple, it ABSORBS green - leaving the purple arrearance you see. So what you see is the light that hasn't been absorbed - which is where the subtractive part comes in!.