An opamp refuses to integrate....

Discussion in 'The Projects Forum' started by envytea, Jun 25, 2008.

  1. envytea

    Thread Starter Member

    Feb 18, 2008
    10
    0
    Dear World,

    So, I am just starting to mess around with op amps, and I am already running into trouble. I just completed having built my first dual power supply, and it totally worked! Now I am trying to get a TL082 to function as an audio oscillator. I have posted a schematic here. This circuit is intended to produce a square wave at one point; then, a triangle wave, after integration, at another point. However, I can only get a square wave off of the circuit. When I tap in my headphones at pin 7 and ground, there is a square wave. Yet, pin 1 hasn't a triangle wave. This suggests that the integration portion of the circuit is not operating. Why is this? I am looking to get a triangle wave between pin 1 and ground. I have it wired, as is, on a bread board. The power supply is a 15+/gnd/15-. The capacitor is a non-polar mylar cap. The 100K resistor is variable; I want to have a range of frequencies. All other details seem to be explained int the diagram I am posting. I am planning on changing the capacitor to a 1 uF to lower the frequency, for I'd like to use this as a low frequency oscillator. What is wrong? All is surely connected correctly. Pin 1 gives no wave, just a stagnant charge. I feel like some resistor values need to be changed. The variable R is at 100K, so do the other Rs need to be on a similar scale? This circuit, in order to work properly, needs to have the two other resistors at a similar value, yet one larger than the other. What's up? Any one know what needs to be changed? I'd love to know what is wrong. Might you too be able to tell me 'why' it is screwed up? I need to learn this stuff....

    Any help would be absolutely appreciated. Good day.

    -Nick
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    You might try drawing schematics using symbols, that is more of a printed circuit board layout, very hard to read. Also, use .png formats, they are much smaller and don't loose any resolution. Third, there is an album section here at AAC you could have used to place it, and then link to it. If you don't have any drawing programs you can use my PaintCAD found on my blog, or some other electronics graphic program. I'll try redrawing what you have and then post it in a few...

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    [​IMG]

    See the difference? Betcha you can figure it out yourself now.
     
    Last edited: Jun 26, 2008
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
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    Suggestion for oscillator, look up op amp Schmitt Triggers, then feed it back with an integrator. I have a similar project going.
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    I corrected your pcb layout.
    The pot should have a 2k resistor in series to prevent its value from going below 2k ohms.
     
  5. envytea

    Thread Starter Member

    Feb 18, 2008
    10
    0
    Thanks y'alls.

    Audioguru,
    I actually misrepresented my circuit diagram. Indeed, I do have the circuit laid out as you have corrected it; I just incorrectly diagrammed it. So, I think may have a bad opamp here. I've been running the circuit without the 2K resistor, and I may have damaged something. Shoot. Furthermore, I powered the opamp with over 16+/- vdc; more nearly to 17 volts. Oops... This all may have led to malfunction. Having another opamp, yet to be used at all, I am going to try again with the resistor in place and a lower voltage supply. We'll see what happens. I'll give it a try tonight and report back shortly. You continue to make help me, and I owe to you an abundance of my worth. Let me know if you ever need anything. I am trying to figure out so may things, and having only a background in basic college physics, I am climbing a steep hill. Your help has been remarkable. Thank you.

    Marsden,
    I will check out the blog of your's. The circuit diagramming software sounds sweet. Thanks. I hope it runs on Linux.

    Peace all,

    Nick
     
  6. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    It is basically a bunch of template designed to be copied and pasted onto a blank sheet, that will be your diagram. I use Paint, but it can be any graphics program. I suspect it is very open source the way it is laid out.
     
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