FSK demodulator does not move my servo

Discussion in 'The Projects Forum' started by ayashifx55, Apr 15, 2011.

  1. ayashifx55

    Thread Starter New Member

    Dec 17, 2010
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    Hello guys,

    I'm having a school project. I am making something remote controlled. I have a PWM (555 timer) going to FSK (to convert my square wave into sinewave) and transmtiting through VCO. Then i have PLL VCO as receiver which goes into my FSK Demodulator, it converts the sinewave (0-1) back to squarewave.

    I tried controlling my servo with my PWM , works perfectly, precise reaction and movement. Tried directly PWM to FSK , FSK to FSK-DEMO .. servo goes crazy and does not react right. Moves back and forth repeatly where my original PWM , it only moves according to my PWM width is changed (by moving my pot)

    Q: Is it because the FSK-demod is not producing the right current?

    [​IMG]
    This picture shows my PWM (top) and my FSK Demodulated signal (bottom, does not react to servo, servo goes crazy....)

    FSK i use XR 2206 and FSK DEMO i use XR 2211 , thank you very much for your help.
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Can you post the demodulator circuit? The waveform looks right, but what is the output impedance and voltage?
     
  3. ayashifx55

    Thread Starter New Member

    Dec 17, 2010
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    I am using this design of 2211, 300 baud [​IMG]

    Voltage can be varied according to the VCC i input. I don't know about the output. I am thinking if its because the FSK demod does not output enoug current to control the servo? The output of the FSK demod has like .1mS loss VS the original PWM but that shoulnt make it go crazy right?

    One thing to note is that my RL and RB is not equal to 510k and 5.1k , does that matter much??
     
  4. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    I have no idea if the resistors matter much, but if you can see the right signal with an oscilloscope on the output, then you need some output buffer.
    What is your supply voltage?
     
  5. ayashifx55

    Thread Starter New Member

    Dec 17, 2010
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    With direct connecting, from PWM to FSK , from FSK to FSK DEMOD , i can get an output PWM of 5-10V depending on how much VCC i give.

    As for output buffer, do you recommend power amplifier such as emitter follower circuit to improve my signal current?

    Like i mentioned, PWM controls my servo perfect if i directly give signal from PWM to servo but if i give the output of the FSK DEMODULATOR to the servo,it will go crazy.

    I tried wirelessly, servo woulnt even budge. Thank you very mcuh!
     
  6. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Yes, a simple emmiter follower should be enough.
     
  7. ayashifx55

    Thread Starter New Member

    Dec 17, 2010
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    i will give it a try kubeek and show you the results, thank you for your support ;)
     
  8. ayashifx55

    Thread Starter New Member

    Dec 17, 2010
    21
    0
    i forgot to ask you something kubeek,

    My screenshot of both output seems fine but im having a problem on the "high"
    The type of caps i use are ceramic disks (very small ones) Not sure if it affects the "moving" problem.
    The half end of the high just goes back and forth.

    Does it have something to do with the caps of the fsk demod?
    Because some values like 0.039uF and 0.005uF , i only chose values closest to it like 0.047uF and 0.0047uF


    Thank you very much!!
     
  9. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Can you post that screen?
     
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