interactive led coffee table design suggestions...

Discussion in 'The Projects Forum' started by onlyvinod56, Feb 3, 2011.

  1. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
    362
    1
    Hello.
    recently i have seen some hobby projects based on LEDs like LED cube, Interactive led table...etc from instructables.com.

    I want to design the interactive table.
    http://www.youtube.com/watch?v=IkmpIXd9Q90&feature=player_embedded
    I didnt find the details of the IR emitter and receiver.
    can anybody suggest me a low cost pair?

    I have a doubt,
    Both the IR diode & transistor are facing upwards. when an obstacle comes, the IR rays reflects and fall on the receiver. thats what i understood.
    Suppose, if i remove the internal parts of MOC7811 and used seperatly to face upwards, does it works????

    I dont have a detailed idea about this photo electronics.
    Is it necessary to give a pulse type signal to the IR diode???
    Does it works if i give continuous constant signal to the IR diode???

    I feel happy if anybody post some web links.
    thankyou.
     
    Last edited: Feb 3, 2011
  2. wayneh

    Expert

    Sep 9, 2010
    12,107
    3,038
    Yes and no respectively. The receiver will only react to a frequency it is designed for. This allows it to ignore ambient light. Just google around and read datasheets for the IR receiver modules, for instance from Sharp. They describe well what is needed and how they work.
     
  3. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
    362
    1
    Thankyou wayneh...
    Ok. Just now, i hav seen the receiver module. It looks the circuit becomes complicate if i use it.

    Is there any other thing like photo diode & photo transistor?
    OR can i do it with an LDR??
     
  4. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
    362
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    • IR.JPG
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  5. wayneh

    Expert

    Sep 9, 2010
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    LDR? Don't know that one.

    I think you'll be unhappy trying to make your own "simpler" sensor using light, if you don't use the commercial device designed for that purpose. It will be quirky and less effective, and in the end no simpler at all.
     
  6. wayneh

    Expert

    Sep 9, 2010
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  7. magnet18

    Senior Member

    Dec 22, 2010
    1,232
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    I believe the OP is referencing a Light Dependent Resistor.
    More light, less resistance.
     
  8. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
    362
    1
    Ok..

    please tell me, if i placed the photodiode & photo transistor facing upwards, do the rays reflect???
     
  9. wayneh

    Expert

    Sep 9, 2010
    12,107
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    Ah, like a CdS cell or such. Got it.

    The problem is varying ambient light. Without modulation, it's very tough to get the right sensitivity, or signal-to-noise.
     
  10. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
    362
    1
    Exactly magnet18
     
  11. wayneh

    Expert

    Sep 9, 2010
    12,107
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    Well, those are both receivers, but yes, IR light reflects just like visible light. Different surfaces will reflect differently, but in general the reflection strategy should work.
     
  12. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
    362
    1
    yes, both are receivers. sorry i didnt observe that.
    What they'll receive? IR rays or visible light??
     
  13. EsDorlion

    New Member

    Dec 24, 2010
    8
    0
    Hi onlyvinod56,

    I am really related with this led table. I have designed a few demo about this. I tried a few sensors which are pir sensor, GP2Y0A21 Sharp distance sensor, pna4602m and an ir led, and the last one a phototransistor with ir led. I desinged the effects of lights with pic16f84a. Actually they desinged their table with a phototransistor and ir led for sensor. No any microcontroller. i have their circuit schematics. Also they used opamps in this table. if you want i can share schematics with you.

    I want to mention the sensor which i used. The pir sensor is really good to detect the human body but it really slow. Sharp sensor is works good in 10cm-80cm but it is really expensive for this project. it is not suitable. Pna4602m or phototransistor is really suitable and cheap but i have a problem about these to sensor. If you design a table you have to put yor circuit behind a glass. And some of ir light reflect from the glass. So this reflection effects your circuit.

    Now i am trying a new solution with ir led, phototransistor and opamps. I really want to design this table. you can contact with me. we can share our informations. Maybe we can design it together.
     
  14. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Will This do for the sensor?
     
  15. EsDorlion

    New Member

    Dec 24, 2010
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    İt is a good product but it is expensive for this application. If you design a 40cmx80cm table you will need almost 12 sensor. So it is not suitable
     
  16. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I bought one just to experiment.

    How about Photo diodes?
     
  17. EsDorlion

    New Member

    Dec 24, 2010
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    [​IMG] D1 is a phototransistor
    You can use photodiode or phototransistor as a voltage divider under the normal light in a room. For example if you look the picture above, in a bright environment Vo=5V but if you shade it the voltage will reduce. You can use this voltage easily as an input for a microcontroller but when the room is dark your photo diode doesn't work. Vo=0v. Because it needs light. But if you put an ir led near the photodiode and put your hand on it, you will see the voltage at Vo start to increase. So you must determine a medium voltage both dark and bright environment.
     
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