Infrared circuit not working

Discussion in 'Homework Help' started by regal006, Aug 23, 2012.

  1. regal006

    Thread Starter New Member

    Jul 14, 2012
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    i can't make this circuit work. :(
    how do you make an infrared circuit that will have a range of 2 - 3 meters.
    i've been doing this circuit for days..
    please help..

    thanks a lot!
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Days huh! :rolleyes:

    Why don't u try increasing the drive current via the IR emitter by employing a transistor.
     
  3. regal006

    Thread Starter New Member

    Jul 14, 2012
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    thanks. but it still doesn't work.
    btw, why do i need to use 555 ?
    infrared doesn't work on pure dc?
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    It will work.

    Using pure DC is less efficient. The 555 will pulse the led. This will increase the distance and efficiency.

    I know u did not try what I suggested. but try putting more IR leds in parallel but for this a transistor is necessary.
     
  5. absf

    Senior Member

    Dec 29, 2010
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    I think you connected the infra LED D1 polarity wrongly. When the output of 555 is high, the led wont conduct due to both Anode and Cathode are at same potential. When output is low, D1 would not conduct as the polarity of LED is wrong.

    The negative supply of the 741 was not connected too. Where is the -9V for the 741?

    Allen
     
  6. regal006

    Thread Starter New Member

    Jul 14, 2012
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    @R!f I did but it still doesn't work.

    @absf i tried different turning the ir led and the phototransistor . i even used photodiode. still nothing happens

    sorry forgot to put ground on op amp
     
  7. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Then u need to modulate it to a higher frequency.
     
  8. regal006

    Thread Starter New Member

    Jul 14, 2012
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    how high? how about crystal?
     
  9. regal006

    Thread Starter New Member

    Jul 14, 2012
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    here is the real schematic
     
  10. absf

    Senior Member

    Dec 29, 2010
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    Yes I agree with R!f@@, modulate it to a higher frequency is a good idea. Say around 20KHz would be fine.

    Here is a 555 calculator so you can pick the value of R1, R2 and C to get the osc freq you want,

    http://www.ohmslawcalculator.com/555_astable.php

    Allen
     
  11. MrChips

    Moderator

    Oct 2, 2009
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    What is C2, 1μF across IC2 in the original circuit for?
    Also I think you have the +ve and -ve inputs reversed.
    I guess I don't know what that circuit is trying to do.
     
  12. regal006

    Thread Starter New Member

    Jul 14, 2012
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    i don't know either what the op-amp does with this. :(
    anyway . i'll do what they said. i'll come back later this evening if i still doesn't make this circuit work. need to go to school.

    thanks a lot for those who replied
     
  13. absf

    Senior Member

    Dec 29, 2010
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    I changed your circuit a bit and it worked.

    The U2 op-amp is used as a comparator. When the photo transistor detects a signal it conducts and thus lower the voltage of the negative input of the opamp. The reference at + input is set to 1/2 Vcc. When no signal is detected, the output is low so the LED is off.

    My simulator doesn't have the IR led and photo transistor so I used an opto coupler instead. I put a button on the transmitter so you can test the Rx and also saves the battery life.

    Allen
     
  14. regal006

    Thread Starter New Member

    Jul 14, 2012
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    thank you all!. finally i got it working.
    i just made my infrared oscillate arount 20khz! thanks!
     
  15. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Did you make any changes to your circuit? Which circuit did you use, the one from your notes or the one you posted in your original inquiry
     
  16. regal006

    Thread Starter New Member

    Jul 14, 2012
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    i use the circuit from my notes. i just tweak the 555 circuit to oscillate at 20khz.
     
  17. JoeJester

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    Apr 26, 2005
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    You do realize the infrared led in your notes is also backwards, however, if it is working, you wired it in properly.

    And the "receiver" in your notes is not a comparator.
     
  18. regal006

    Thread Starter New Member

    Jul 14, 2012
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    how? i thought 741 is a comparator?
     
  19. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    741 is an op amp

    You can use it in a comparator circuit, but that is not what you have drawn. You have a reference of zero volts but zero chance of crossing that threshold to change the output state. absf has shown the 741 in a comparator circuit in his drawing above.

    Can you explain the receiver circuit you have drawn on your notes?
     
  20. absf

    Senior Member

    Dec 29, 2010
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    All comparators have open collector/drain outputs.

    Allen
     
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