741 Op amp problem, help needed!

Discussion in 'General Electronics Chat' started by ja7me, Sep 20, 2012.

  1. ja7me

    Thread Starter New Member

    May 24, 2012
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    Hello everyone,

    I am new to electronics and have been experimenting with the 741 op-amp.

    The op amp behaves exactly how I expect it to on multisim electronics simulator program. However when I build the circuit on breadboard it behaves differently. Below I will try to explain this difference I am getting:

    On simulator:

    In the attached schematic I have set the gain to 10, therefore 0.2V in should equal 2V out. And 0.4V in should equal 4V out. This is what I get, which is what I expect.

    On breadboard:

    When I tested using breadboard I used a variable resistor in replace of R12 (on schematic) to set a gain of 10. This worked fine as 0.2V in equalled about 2V out.
    However, when I increased the input voltage to about 0.4V, I was still getting 2V out. I believe this to be incorrect behaviour.

    Below are some measurements I took:

    0.2V in:
    Pin 2 = About 1.8V
    Pin 3 = About 0.2V
    Pin 6 = About 2V

    0.4V in:
    Pin 2 = About 1.8V
    Pin 3 = About 0.4V
    Pin 6 = About 2V

    I really would appreciate any help on understanding this issue.

    Kind Regards,

    Jay
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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  3. t06afre

    AAC Fanatic!

    May 11, 2009
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    The lm741 need a dual supply to work properly. A dual power supply is something that gives out both a positive and negative voltage. You can easy make this from say two 9 volt batteries. However I would not recommend using the 741 opamp at all. Use a more modern opamp. For the setup you have try to use the LM324 opamp. Yes it is kind of old school that to. But it is designed for single supply applications and also very common world wide.
    You should also be aware of that simulators do not always give a real world result. They are like a very theoretical professor that never have done done some real world design work. Very good at math but that is also all ;)
     
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  4. justtrying

    Active Member

    Mar 9, 2011
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    but 741 is good to practice you patience and trouble shooting. Try it again with dual supply and also keep in mind that you should see same voltage on pins 2 and 3 if the op amp is functioning properly.
     
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  5. bertus

    Administrator

    Apr 5, 2008
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  6. t06afre

    AAC Fanatic!

    May 11, 2009
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    And as the first car for a new driver I would recommend this one. The Volkswagen Type 1. Good to practice your patience and trouble shooting:p No I want the new driver to have something better. And I want the electronics beginner to start of with something else than the LM741
    [​IMG]
     
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  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    I vote that this should be the title of a sticky......:rolleyes:

    Hence the reason for breadboarding EVERY circuit.
     
  8. Audioguru

    New Member

    Dec 20, 2007
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    What is wrong with learning to drive in the old Volks bug? I did. It didn't tip over and never spun around.

    I tried a lousy old 741 opamp once long ago. Its limited input and output voltage range, its output hiss and its problems with frequencies higher than only 9kHz caused me to never use it again.
     
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  9. Audioguru

    New Member

    Dec 20, 2007
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    I designed and soldered together hundreds or thousands of circuits and never used a breadboard with its intermittent contacts, stray capacitance and inductance and hundreds of wires picking up interference.

    The circuits were designed using minimum or maximum allowed spec's in the datasheets. Some circuits were extremely complicated.
    Every circuit worked perfectly and frequently the prototype was sold.
     
  10. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    "Breadboard" is a general term for a circuit constructed for only one or two copies using methods available in a small shop using hand tools, though I would not count out a custom PCB.

    When I breadboard a circuit I tend to use boards with plated thru holes on 0.1" centers with connections soldered together using 30 awg Kynar wire for signals, and solid #26 bus wire for power.

    The "solderless breadboard" is an abomination straight from hell only good for the most non-critical applications. I have not used one in decades. They may be of some assistance to the beginner but should be abandoned ASAP.
     
  11. Eric007

    Senior Member

    Aug 5, 2011
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    :D LOL...that's TRUE tho and my dad always *laugh* at those *professors* full of theories (very good tho) BUT with no real world design/application EXPERIENCE!!
     
  12. Audioguru

    New Member

    Dec 20, 2007
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    All the school kids that come to these forums complain that the circuit they copied (they stole it) doesn't work. After many questions they admit they built it on a solderless breadboard.
     
  13. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    The term "breadboard" does not imply it has to be a protoboard or pinboard, most are some kind of soldered kluge. The original term "breadboard" was given because people drove brass pins into an actual breadboard and soldered to them as point to point connections to make a circuit.


     
  14. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    And that is the single most important lesson they will learn in school: circuits have to be IMPLEMENTED into the real world correctly, you can't just print out the crap the simulator gave you and hand it off to the guy doing a PCB layout in PROTEL or whatever brain dead software is the latest fad.

    It takes ENGINEERING KNOW HOW to lay out any circuit... and the higher the current and/or frequency of operation, the harder it is to lay out properly so it will work.
     
  15. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Like a blank piece of copper clad board with grooves cut in it using a Dremel with a diamond tip cutter. I used to crank those out at warp speed..... great for home projects.:D

    That was the original surface mount technology......
     
  16. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
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    Yep, DC only low current circuits. Like any and all tools, should only be used by somebody who knows exactly what the limitations are.
     
  17. ja7me

    Thread Starter New Member

    May 24, 2012
    18
    1
    Thanks for all your responses guys. I will try experimenting with different types of op amp, especially the more modern types.

    :)
     
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