Color sensor distance problem

Discussion in 'The Projects Forum' started by vosvos450, Oct 19, 2008.

  1. vosvos450

    Thread Starter New Member

    Sep 30, 2008
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    Hi,

    I want to detect three colors(RGB) by using a circuit.I tried LDR and three leds(red,green,blue) but they are not sensitive.For example I can not detect colors more than 5 cm away.It should detect at least 10 cm away from LDR.

    What do you suggest?Should I use other thing?
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    Can you give us information on the circuit (schematic).
    Have you been looking at teh RGB sensor of AVAGO?
    In the datasheet a blockdiagram is given.

    Greetings,
    Bertus
     
  3. DickCappels

    Moderator

    Aug 21, 2008
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    The simple answers (without understanding what you are trying to do):
    1. Use LEDs with higher output power.
    2. Use focusing ptics to extend the range.
    3. Use some gain to amplify the output of the CDS cells.

    Certainly, with a CDS cell, blue will be a problem. There may be silicon sensors with better blue response than CDS.

    And of course if you can get the Avago sensor that Betrus mentioned, it would make things a lot simpler.
     
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Another commercial detector option: http://www.taosinc.com/...look at Color Sensors

    To increase your range, three options come to mind:

    1. Increase the amplification of your detector circuit.
    2. Add a lens system to concentrate the light on your detector.
    3. Increase the amount of light shining on your colored surface.

    Ken
     
  5. steveb

    Senior Member

    Jul 3, 2008
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    Without details I don't know if this is useful, but you could use optical filters in front of each color detector. Also, you could modulate the light sources at different frequencies, and make detector circuits that look for those frequencies.
     
  6. vosvos450

    Thread Starter New Member

    Sep 30, 2008
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    this is my circuit.I used two blue leds one for red one for green.Black thing in the middle is LDR.How can I increase the sensibility(range of measurement)????


    [​IMG]
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    You forgot to attach your schematic. Attach it here, not over at ImageVenue.
    The schematic will show the supply voltage, the LED driver and the series current-limiting resistor so we can see how much current there is in the LEDs.

    The schematic will show if something is loading down the variable resistance of the LDR's.
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    That is not a circuit - it is the arrangement of the parts. Can you post up a schematic? Something about 4 times larger than the fuzzy image, please.

    By the way, KMoffett's link to the TAOS devices is a good one. A LED is very insensitive by comparison. You would need color filters, though.
     
  9. vosvos450

    Thread Starter New Member

    Sep 30, 2008
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    Finally,I make some comparison and show the color...

    Here is what you want...
     
  10. beenthere

    Retired Moderator

    Apr 20, 2004
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    I would think that to use a LED as a color sensor you would have to bias each LED to a point where is was just barely conducting and do the sensing between the resistor and the LED.

    That can't be your schematic, by the way. Where is the CDS cell? What function does it provide? The uC can't possibly pull up the LED's and measure conduction at the same time.
     
  11. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    I think he's lighting the colored LED's one at a time, and measuring the voltage at the resistor/LDR voltage-divider, on the left of the µC. That gives him one value for each of three colors.

    Ken
     
  12. vosvos450

    Thread Starter New Member

    Sep 30, 2008
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    yeah thats whAt I do...

    I dont know how I increase the range...
     
  13. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    From my earlier suggestions:

    #1...Add an opamp with gain and adjustable offset between the voltage divider and the PIC's ADC input.

    #2...Judging from the image of your LED/LDR arrangement this might be possible. A lens over the LDR, and tilting all three LEDs to aim at a single point on the colored surface.

    #3...If you drive the LEDs with more current you get more light and more response from the LDR. You can briefly drive LEDs with much more current than their continuous max rating of usually 20mA. This would probably require an external drive BJT transistor or MOSFET so as not the exceed the PIC's output current rating.

    Ken
     
  14. boff1

    Member

    Oct 15, 2008
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    Why don't you try using 3 sensors and 3 colour filters - red green and blue? Read the output from each sensor. The highest value will indicate the colour to the lamp that is lit.
     
  15. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    I think he's trying to determine the color of the surface that is reflecting light from the LEDs back to the LDR. Maybe 3 LDRs with colored filters, and a white light source. I don't know if one, or more, white LEDs would work for him.

    Ken
     
  16. raufjaleel

    New Member

    Apr 17, 2010
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    Color Sensors are commercial products not a textbook topic, so nobody will 'share' his commercial activity/ technique/ etc. with others. People will provide you awareness but not "turn key solutions".
     
  17. retched

    AAC Fanatic!

    Dec 5, 2009
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    Sorry raufjaleel, you are 2 years late on this thread. But, It may help someone that is googleing for this info.
     
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