IR shaft encoder

Discussion in 'General Electronics Chat' started by h.d, May 1, 2008.

  1. h.d

    Thread Starter Active Member

    Oct 22, 2007
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    hi all
    i implemented the follwing shaft encoder circuit
    but the output voltage is very low(2V)
    it should be around (4V)
    i dont know what the problem.....anyone can tell me....?????
    and thanks
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    The detector circuit is not an ideal one.

    The first thing I notice is that the IR photodetector has no current flowing through it. This is due to the fact that the input current at the opamp is pretty close to zero.

    Something quick you may try is placing a 1K feedback resistor between the output of the opamp and the negative input. Then adjust your potentiometer so see if you can bias the opamp's positive terminal to produce an output change when you expose it to the IR source.

    hgmjr
     
  3. h.d

    Thread Starter Active Member

    Oct 22, 2007
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    i try it but it dosen't work..
     
  4. h.d

    Thread Starter Active Member

    Oct 22, 2007
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    when a touch the transmitter legs the output voltage increase to be 4V
    i dont know if that means anything!!!!!:(
     
  5. hgmjr

    Moderator

    Jan 28, 2005
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    I suggest you visit www.discovercircuits.com and go to the schematic section and search on IR detectors. Dave Johnson has posted a number of circuits that you can use as examples.

    hgmjr
     
  6. hgmjr

    Moderator

    Jan 28, 2005
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    It would appear from your schematic that you are using two IR emitters. Am I interpreting your schematic wrong?

    hgmjr
     
  7. hgmjr

    Moderator

    Jan 28, 2005
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    You need a detector and an emitter.

    hgmjr
     
  8. h.d

    Thread Starter Active Member

    Oct 22, 2007
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    i try the two ways
    trx-trx and trx-x
    its from that link
    ikalogic.com
     
  9. hgmjr

    Moderator

    Jan 28, 2005
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    It would be helpful for you to post the part numbers of the IR emitter and the IR detector you are using so that we can consult the datasheet for each.

    hgmjr
     
  10. hgmjr

    Moderator

    Jan 28, 2005
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    Not exactly sure what you mean by this statement. Can you clarify?

    hgmjr
     
  11. h.d

    Thread Starter Active Member

    Oct 22, 2007
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    i mean that i use transmitter and reciever
    and 2 transmitters
    but its the same result...
    i dont have serial numbers
    its IR leds
     
  12. hgmjr

    Moderator

    Jan 28, 2005
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    I visited the link you provided and I see the circuit you are using. The author is apparantly using the emitter to perform both the transmit and detect function.

    I have not seen that implementation before.

    hgmjr
     
  13. hgmjr

    Moderator

    Jan 28, 2005
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    Give the website www.discovercircuits.com a look and see some of the examples of IR circuits they have available.

    It is certainly possible that your IR devices may have been accidentally damaged.

    hgmjr
     
  14. hgmjr

    Moderator

    Jan 28, 2005
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    If you have digital camera or a cell phone camera you can use that to test the IR emitters to see if they are operating in the emitter mode.

    hgmjr
     
  15. hgmjr

    Moderator

    Jan 28, 2005
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    Work calls.

    I will leave you with one of the other members to assist you in debugging your circuit.

    hgmjr
     
  16. h.d

    Thread Starter Active Member

    Oct 22, 2007
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    ok i will try the camera, and wait the assistant from our forum members.
    thanks for your time
     
  17. hgmjr

    Moderator

    Jan 28, 2005
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    Assuming your IR LEDs are operating, you may have a problem with ambient light. Some conventional lights fixtures can emit a small amount of IR light. If you happen to be testing the circuit in an area that has some ambient IR light, the circuit may end up being triggered by this ambient IR light source. It may be worthwhile to test your circuit in a low light environment in case that is preventing your detector from working properly.

    hgmjr
     
  18. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Looking at your receiver circuit:
    1) Remove R5.
    2) Remove the IR-sensitive diode, and replace it with a piece of wire.
    3) Put the IR-sensitive diode where R5 was.

    (See the attached)

    You should now get at least some kind of response.

    You are running the LM358 in open-loop gain mode. This is not recommended for operational amplifiers, because it means that the output will be constantly saturated, ie: maximum current dissipation. You should provide a feedback path, even if it's only a 100k resistor. This is shown as R4 in the attachment.
     
  19. h.d

    Thread Starter Active Member

    Oct 22, 2007
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    i try it wi th and without ambient light......the same result us acheived.
    i will exchange the IRLED's another time.
     
  20. hgmjr

    Moderator

    Jan 28, 2005
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    Were you able to test the IRLEDs to confirm that they are illuminated when viewed using a ordinary digital camera or cellphone digital camera?

    Be sure that the IRLED is powered in the correct polarity.

    hgmjr
     
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