Need help with Wien-Bridge Oscilator

Discussion in 'Homework Help' started by purpleclover, May 26, 2013.

  1. purpleclover

    Thread Starter New Member

    May 26, 2013
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    Greetings everyone, i have a assigment and i need to creat a wien bridge oscilator that uses potentiometers so the out frecv can be modified between (10, 14 )Khz...and the out voltage between (6,9) V ... i allready made a sketch but i just cant figure out how to do this...every time i try to make the amplitude bigger the frecvency changes and the other way around. Please, can someone help me ?
     
  2. Ramussons

    Active Member

    May 3, 2013
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    I don't see any potentiometers in the schematic.
    If I recall the Wien Bridge oscillator working, you need to use 2 opamps, one each for frequency and amplitude.

    Ramesh
     
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  3. purpleclover

    Thread Starter New Member

    May 26, 2013
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    Thanks Ramesh for your reply. I didnt add any potentiometers since i didnt really know wher e to put them ...could you please make a quick sketch on how to place the 2 op ams?...dosent have to be exactly just a quick paint sketch so i get a basic ideea cause im preety lost here:(
     
  4. Ramussons

    Active Member

    May 3, 2013
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    spark8217 and purpleclover like this.
  5. purpleclover

    Thread Starter New Member

    May 26, 2013
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    okay. Thanks alot!
     
  6. Shagas

    Active Member

    May 13, 2013
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    I'm actually battling with a Wien bridge at the moment...
    Use http://www.learnabout-electronics.org/Oscillators/osc34.php
    as Ramussons pointed out . It gives a good overview on WIEN stabilization using diodes or a JFET.
    The Variable Wien with the 2 diode stabilization works fine . You will need c1 and c2 to be about 1nf . And use stereo potentiometers to get the variable frequency (I actuallly use two H11F1 JFET optocouplers so I can vary the resistance with one mono potentiometer) .
    Mine gives an output of about 200mv at the lower frequency end and 1 volt at the higher end .

    Don't bother with the amplitudes inside the oscillator itself because it's going to be pretty difficult/not possible I think . Just make it give a good sine wave .

    What you want to do is feed the output of your oscillator into an another op amp and bring up the gain to the voltage that you need .

    I'm currently working on a stabilization method on the amplifying op amp which will give me a solid constant amplitude irregardless of the oscillator output amplitude and frequency.
    Drop me a PM if you need some troubleshooting info i'll let you know on what info I've gathered until that point .
     
    Last edited: Jun 1, 2013
  7. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    The attached simulation schematic [based on Jim Williams design] gives very good amplitude regulation and low distortion over a 10:1 frequency range.
     
  8. Shagas

    Active Member

    May 13, 2013
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    Nice thanks !

    What does a 10:1 frequency range mean ? One decade? or 10 decades?
    I'm guessing the one decade :)
     
  9. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Yes - one decade. I would anticipate the amplitude control would extend beyond a one decade frequency range. How great a range would depend on the control loop dynamics.
     
  10. Shagas

    Active Member

    May 13, 2013
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    A decade is a range ten time too small for what I need but I thank you for the info nevertheless , i'll definately check out how the guy controlls the amplitude in the schematic
     
  11. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    If you can achieve a 2 decade frequency span with stable amplitude control, low harmonic distortion and minimum settling time without range switching, that will be a significant design achievement. Let us know how you go with the project.
     
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