Strange Op-amp circuit...

Discussion in 'The Projects Forum' started by T3chNique, Dec 22, 2014.

  1. T3chNique

    Thread Starter New Member

    Dec 22, 2014
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    Hi everyone, first time user here.

    I have a reasonably good background in electronics and electrical circuits and I decided to tackle on this project:



    but on a smaller scale first for troubleshooting...

    My problem lies in this op-amp setup:

    http://imgur.com/rMK8J8I

    I will be using the LM324N Op-amp instead of the TLC274 op-amp he uses in his video. They are very similar.
    The problem arises with the infra-red reciever/photoresistor signal amplifier.

    As seen in the screenshot above he connects the IR's anode to the non-inverting input on the op-amp and a 10M resistor to ground (pull-down?). He then joins the inverting input to the op-amp's output which creates negative feedback if I'm not mistaken?

    The things I do not understand:
    1. Where are all the resistors to set the op-amp's gain?
    2. Why is there a 10M resistor going from the non-inverting input to ground?
    3. Should there not be a resistor between the inverting input and op-amp output?

    I have include a schematic I have created to aid anyone willing to help me :)

    Schem:
    aaaaaalll the way the left :)

    http://imgur.com/IhItULj
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    What are the 33Ω resistors doing there (e.g. R17???)

    You better look at the input bias current of a LM324 if you are trying to sub it for a TLC274
     
  3. T3chNique

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    Dec 22, 2014
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    Those are current limiting resistors for the photodiodes
     
  4. MikeML

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    For the receiving photodiodes?????
     
  5. T3chNique

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    Dec 22, 2014
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    SORRY they are PHOTOTRANSISTORS not PHOTODIODES

    Yes they aren't ICs, they contain a cathode and anode, Foward voltage drop is 2.2V @ 100 mA, and I'm using 5V to power it with

    and the op-amps have an input bias current difference of 20 nA, I don't suppose it will make that much of a difference or what do you think?
     
    Last edited: Dec 22, 2014
  6. MikeML

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    They are being used as detectors; not emitters. They are supposed to be unpowered.
     
  7. T3chNique

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    Dec 22, 2014
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    Sorry I edited my previous post... they are photoTRANSISTORS not photoDIODES
     
  8. bertus

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    Apr 5, 2008
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    Hello,

    What is the part number of the photoTRANSISTORS?
    Have a look in their datasheet to get more info.

    Bertus
     
  9. T3chNique

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    Dec 22, 2014
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  10. MikeML

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    The opamp schematic on Imgur shows a two-terminal photo-diode used as a detector with a 10meg load resistor. That is why the opamp needs to have very low input bias current.

    btw- I hate having to go off site to see your pictures. Post them here instead of a external site.
     
  11. MikeML

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  12. T3chNique

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    Dec 22, 2014
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  13. T3chNique

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    Dec 22, 2014
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    Sorry first time poster... Will do in the future! Thanks :)
     
  14. MikeML

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    So who do you believe?
    The guy that made the product and wrote it's data sheet, or some kid that works for a store that made a web page?
     
    JohnInTX likes this.
  15. T3chNique

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    Dec 22, 2014
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    Maybe they linked the incorrect datasheet to the product?
     
  16. bertus

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  17. T3chNique

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    Dec 22, 2014
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  18. MikeML

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    Now that you have figured out that the LIR132 is a reciever, do you still think you need the 33Ω resistor?
    Do you still have questions about the opamp?

    Here is the relevant data for the receiver:

    det.gif
     
    Last edited: Dec 22, 2014
    T3chNique likes this.
  19. GopherT

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    Nov 23, 2012
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    The video in post #1 is one of the worst demonstrations of patience and tenacity I have ever seen. To clarify, I mean, this guy has the patience of Job (pronounced "Jobe") but his high-speed editing work make this look like an afternoon project.

    He is really a perfectionist and clearly understands his project and I am sure he will not have a bad connection in the 600 or more solder joints he will make - hundreds of wires to strip and hundreds of Components to place and glue. I didn't even have the patience to watch to the end of the video but, whoever starts this project will have a major investment in components and a firm understanding of the time commitment to complete this project.

    I imagine this could be like one of those hooked rug projects from the 1970s. Everyone saw how cool they looked in the craft store but there were few ever completed. I found my mother's 1/4-done rug when we packed up her house several years ago. Very tedious.
     
  20. T3chNique

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    Dec 22, 2014
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    I was just worried that it would draw too much current? Now knowing that is is a receiver, is my wiring still correct?

    and in regard to the op-amp... What EXACTLY is the 10M load resistor for? I thought the input bias current wouldn't need a current limiting resistor?
     
    Last edited: Dec 22, 2014
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