Variable Frequency function generator ( HELP )

Discussion in 'The Projects Forum' started by ruwad, May 11, 2012.

  1. ruwad

    Thread Starter New Member

    May 11, 2012
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    In my college we were asked to make a variable frequency function generator that make ( sine , square , sawtooth ) waves ,
    i know that if i had a sine wave i can convert it using a zero detecting circuit with an op-amp to a square wave then using an op-amp as an integrator i can change it into a sawtooth wave BUT my main problem is to build a simple sine wave oscillator with variable frequency ,
    i tried many oscillators ; wein bridge , colpitt , crystal and yet i cant find anything that works , if anyone can help please ??
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    A Wien bridge oscillator works perfectly and is very simple. Post your schematic so we can show you what was wrong.
    Colpitts or crystal oscillators are also simple but are used for radio frequencies. Opamps do not work at radio frequencies.
     
  3. ruwad

    Thread Starter New Member

    May 11, 2012
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    i have deleted most of my schematics as they arent working :(
    and about Wien bridge oscillator , i have read that its hard to make a variable frequency with it because every component should be calibrated separetly in order to work properly , and personally i would prefer using a crystal oscillator and varying the frequency of the output using a varactor or something , i have read about it but i cant get it to work on my simulator , tried Multisim and Proteus and yet , not working ...
     
  4. ruwad

    Thread Starter New Member

    May 11, 2012
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    here is a picture of what i m working on now , a colpitt based oscillator , but its't working , as u can see from the output its changing very fast and all in pico volts ...

    [​IMG]
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    I have a Wien bridge oscillator made with an audio opamp and its frequency is tuned with a dual-gang variable capacitor from an old AM radio. It uses a Jfet for amplitude stabilization.

    Why are you making a high frequency crystal oscillator that does not have a variable frequency? I think the value of its 1nF capacitors are too high and are shorting the crystal.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    If you're wanting a variable frequency generator, you certainly don't want to use (a) crystal(s); as you'd only be able to adjust the frequency a few parts per million. Crystals are used when you want the frequency range to be very narrow, as in a system clock.
     
  7. t06afre

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  8. ruwad

    Thread Starter New Member

    May 11, 2012
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    after a little digging , i decided to make it with Wien bridge oscillator but yet again non of the simulations bring a result ....
     
  9. SgtWookie

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    Jul 17, 2007
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    Of course it's not working, as you didn't use any parts.
    Oh, wait - you forgot to post your schematic and your parameters used in the simulation.
     
  10. t06afre

    AAC Fanatic!

    May 11, 2009
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    Simulating an analog oscillator may often be a problem. They have problems starting up then simulating. The simulator way to ideal in its approach
     
    Last edited: May 11, 2012
  11. #12

    Expert

    Nov 30, 2010
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    If I may correct the spelling, "The simulator is way too ideal in its approach".

    We need you to tell us what frequencies you want.
     
  12. ruwad

    Thread Starter New Member

    May 11, 2012
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    well , i m just about to give up ......,i was working in the Lab and trying to get it to work and yet cant get to it , can anyone please post a working wien bridge oscillator circuit here ?
     
  13. ruwad

    Thread Starter New Member

    May 11, 2012
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    10KHz or 20KHz , doesnta matter a lot , but 10K would be better
     
  14. t06afre

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  15. DickCappels

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