LM358 operating amlifier & Led

Discussion in 'General Electronics Chat' started by Ignas, Sep 22, 2014.

  1. Ignas

    Thread Starter New Member

    Sep 22, 2014
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    Hello everybody. I have question about light measurement. I have project where I need to measurement light signal using Led sensor. I need to get light voltage of the output signal between 0 V and 3.3 V. So I chose this interval because I will use ADC converter which to have atmega32, so I don't use more voltage interval because I would like to protect controller input from high voltage signal. So I using LM358 operational amplifier and when I simulation with multisim it's working think but when I connect in a real environment is not work and I don't know why is not work. Someone know about this and can help me.
    upload_2014-9-22_18-37-47.png
     
  2. #12

    Expert

    Nov 30, 2010
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    The LM358 isn't designed for inputs within 1.5 volts of its supplies. Here's a chip that I saw yesterday. Look at the differences in input voltage range.
     
  3. Ignas

    Thread Starter New Member

    Sep 22, 2014
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    Emm... Where do you saw that input is 1.5 V? I offered to use this Amplifier. Every time I change amplifier but it's always not work. And It's very important me to know which circuit is need to use.
     
  4. #12

    Expert

    Nov 30, 2010
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    What is a 02BZ2.2?

    From the look of that circuit, it is a Schottky diode with no current applied to it.

    It looks like I read that wrong. The LM358 will accept inputs down to zero volts.
     
    Last edited: Sep 22, 2014
  5. Ignas

    Thread Starter New Member

    Sep 22, 2014
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    I posted it for only that looking circuit, so actually I using simple Led. Just ignore it.
    I working reall envirument with a simple led.
     
  6. #12

    Expert

    Nov 30, 2010
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    So, will the LED produce a voltage of about .943 that can be amplified to 3.3 volts by:

    .943 x (1 +5/2) =
    .943 x 3.5 = 3.3005V?
     
  7. Ignas

    Thread Starter New Member

    Sep 22, 2014
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    Yes, you right.
     
  8. wayneh

    Expert

    Sep 9, 2010
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    Bypass cap on the power supply? Other op-amp in package is stabilized? How long are the leads on the LED "sensor"? This configuration would be very sensitive to noise on the LED.

    Maybe post a photo of your build, and define what you mean by "it not work". What do you observe?
     
    #12 likes this.
  9. #12

    Expert

    Nov 30, 2010
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    In theory, that circuit will work, but I would add a protection diode to the output.
    Other than that, we must look to your assembly skills.
     
  10. #12

    Expert

    Nov 30, 2010
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    Good point wayneh. Some sort of frequency limiting is in order here. Either on the input side or a capacitor in the feedback loop.
     
  11. wmodavis

    Well-Known Member

    Oct 23, 2010
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    You might also look at using a transimpedance amplifier as used in some sun photometer instruments. Here is a link that provides some background and perhaps some information you may find useful. See particularly 4.2 Aerosols (Sun Photometer) and fig 20.
    http://www.instesre.org/papers/UsingTheSun/using.htm#instruments
    I presume you are interested in visible light measurement. The photometer referenced in the article has two photo sensors, one for green light and the other for red, that are within the visible spectrum.
     
  12. Ignas

    Thread Starter New Member

    Sep 22, 2014
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    I not sure for bypass what you are have mean? Yes I think it's stable. Leads is very short. I understand that is very sensitive to noise but I don't get output signal and I don't understand why. So I add my circuit picture.
     
  13. Ignas

    Thread Starter New Member

    Sep 22, 2014
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    But I need to get output signals now is 0 V. Zener diode protection between 0 to 3.3V.
     
    Last edited: Sep 22, 2014
  14. Ignas

    Thread Starter New Member

    Sep 22, 2014
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    [/QUOTE]
     
  15. wayneh

    Expert

    Sep 9, 2010
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    Your IC is inserted wrong. Turn it 180°.

    The power hookups also need to fixed. Check and double check the pinout.

    OK maybe just V+ needs to be corrected. Anyway, check the pinout.

    A bypass capacitor, for instance 0.1µF ceramic, is placed across the power pins. The unused op-amp should be stabilized. The data sheet should address the best way to do that. Or see here or here or here.
     
    Last edited: Sep 22, 2014
  16. Ignas

    Thread Starter New Member

    Sep 22, 2014
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    Thank for posted I will read about it. It's very interesting for me now. :)
     
  17. Ignas

    Thread Starter New Member

    Sep 22, 2014
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    Yes It was wrong I don't connect supply pin...Is so Stupid mistakes. :/ Currently is not sensitive for light or dark.
    My supply is about 7 V. When is dark I get output signal about 3.5 V and light when I turn on the lamp is 4.4 V.
    I need get 0 V when is dark. :( And light 3.3 V. :(
     
  18. Ignas

    Thread Starter New Member

    Sep 22, 2014
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    [/QUOTE]
     
  19. wayneh

    Expert

    Sep 9, 2010
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    I would use a comparator such as LM339 to get your "digital" output.

    But you should be able to use this op-amp as a comparator.
     
  20. Ignas

    Thread Starter New Member

    Sep 22, 2014
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    Do you think if I use this comparator its works well? How does connect circuit?
     
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