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Phase locked loop with 3 ICs

  1. Jan 10, 2014 #1
    Hello,
    I am in need of big help here. I don't know what else should be done to get this correct.
    I have to build this PLL circuit and choose any 3 N (integer) of the N-divider. Then I have to observe the input signal Sig_in and the output signal VCo_Out for each N. The result should be that the output frequency is N+1 times bigger than that of the frequency set by ELVIS (function generator), if I have understood the instructions correctly. I attached my results. The output signal looks weird, right? When I set N as 1, the output signal gets messed up :/ I tried for N= 4 and 8, the waveform looked just the same as when N=1. What should I do? By the way, where should I connect the 5th pin of IC 85 (A=B) to? In the diagram it just shows a short line not connecting to anything.

    I took 4 pictures of different angles so you can see better. Click on the flickr links to see the pictures of my circuit.

    NOTE: THE DIAGRAM IS IN THE PDF FILE PAGE 2.

    http://www.flickr.com/photos/98820721@N04/11870437296/sizes/o/in/photostream/

    http://www.flickr.com/photos/98820721@N04/11870033074/sizes/h/in/photostream/

    http://www.flickr.com/photos/98820721@N04/11870445586/sizes/k/in/photostream/

    http://www.flickr.com/photos/98820721@N04/11869882813/sizes/k/in/photostream/
     

    Attached Files:

    Last edited: Jan 10, 2014
  2. jcsd
  3. Jan 13, 2014 #2

    NascentOxygen

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    Hi MissP. Can you attach a jpeg showing the schematic of your circuit? (I don't do pdfs.)
     
  4. Jan 14, 2014 #3
    There you go!
     

    Attached Files:

  5. Jan 14, 2014 #4

    NascentOxygen

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    The first step is to understand the function of each chip, so that you are able to then judge whether each is performing as expected. What do you understand is the function of the 393 chip? What does it do here?
     
  6. Jan 14, 2014 #5
    The 393 chip serves as a counter. The 74hc393 counts only until the output count equals the setting of the ELVIS switches, I think. If you have A>B line connected to 74hc4046, then you have an output every time A>B.
     
  7. Jan 14, 2014 #6

    NascentOxygen

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    First, we should check that the free-running frequency of the VCO is close to the designed value. Disconnect the wires from pins 14 and 3 of the 4046, and measure the frequency of its output (pin 4). Is this frequency close to what you were hoping for?

    Did you design for a particular free-runnng frequency, or are you just using values for external R's and C's that you have been told to use?
     
  8. Jan 14, 2014 #7
    I am just using values for external R's and C's that I have been told to use. What difference does that make? I actually run a VCO test before and here's the results.

    Left side is V, right side is kHz. I have set the frequence between this range but I still didn't get the result I am hoping for!
     

    Attached Files:

  9. Jan 14, 2014 #8

    NascentOxygen

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    When you have measured the free-running frequency, let me know what it is.

    Also, what frequency Source Clock are you applying to pin 14 of the 4046? You attached 2 schematics,, identical except for that frequency.
     
  10. Jan 15, 2014 #9
    How to check the free-running frequency? I set the reference frequency to 4kHz.
     
    Last edited: Jan 15, 2014
  11. Jan 15, 2014 #10

    NascentOxygen

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    See post #6

    Is that what is labelled Source Clock? Disconnect it, and disconnect other feedback, and the 4046 should oscillate by itself at its free-running frequency.

    BTW, I'm curious to know what your lab instructions say is the goal of this demonstration? Can you quote what the notes say?
     
  12. Jan 15, 2014 #11
    Oh, sorry I missed post no.6.

    Yes, that's the source clock.

    The goal is to get the frequency of this circuit, that is "frequency from ELVIS x (N+1)" even if the waves are not fully locked.
     

    Attached Files:

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    Last edited: Jan 15, 2014
  13. Jan 15, 2014 #12

    NascentOxygen

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    Yes, disconnect from pin 3. Remove the function generator by pulling the wire from pin 14 (that's 14, not 4). Does the 4046 oscillate, if so, what is its frequency?

    Does the blue wire from pin 4 go anywhere?

    Do you have this board at home, or do you have to wait until you next go to school/college/uni before you can test changes to the setup?
     
  14. Jan 16, 2014 #13
    Yes, 14. I mis-wrote that. I don't have the board at home which is a big problem for me so I can't do any changes to the board yet. However, I did a VCO test before by connecting pin no 9 to the variable power source that ranges from 0 to 4 V. The frequency range at 0~4V was 289~528kHz
     
  15. Jan 16, 2014 #14

    NascentOxygen

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    There were 3 questions in my last post. Please address all.

    In post #1 you attached two pics. Can you explain where these signals were found, what you don't like about them, and what you expected they would/should be.
     
  16. Jan 16, 2014 #15
    1. I haven't done that yet because I don't have the tools now. But doesn't the VCO test mean anything here? The result from the VCO test is in my previous post.

    2. Yes, it is the VCO output to channel 2, it is also connected to Clock
     
  17. Jan 17, 2014 #16

    NascentOxygen

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    Also, what factor were you dividing by when the pics were taken?
     
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