PLL IC CD4046 help needed

Discussion in 'The Projects Forum' started by kahafeez, Jan 23, 2009.

  1. kahafeez

    Thread Starter Active Member

    Dec 2, 2008
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    Hi folks, i need to make an FSK modulator and a demodulator.... i came to know abt this IC called 74HC4046 which has the centre/ free running frequency upto 17MHz which would be great for me....

    now i'll start experimenting with the CD4046 first.... see if i could handle it.... if that works for me then i'll go for the 74HC4046 as thats my goal(m nt sure if this is available in my country bt the CD4046 is available and pretty cheap).....

    i tried with the CD4046 before bt just on simulation.... i could not get it to work, i tried for abt a week on it.... may be there was some problem with the sim or i dont know..... bt i'll buy a CD4046 tomorrow and do a few experiments with it..... and i'll get back here and post the results....

    the very first thing which i'm gonna do is to see i can set the VCO's free running freq.... i've posted the schematic which i'm gonna use.... plz tell me if this is ok or not as i'm kind of a newbie..... and i'm also afraid as i've already struggled with it and couldnt get it to work.... plz help me with this.... its very imp for me that this works.....
     
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  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Wich datasheet are you using ?
    Texas or Fairchild ?
    What is the input voltage of the VCO ?

    Greetings,
    Bertus

    PS use proper english, that will make the text more clear.
     
  3. kahafeez

    Thread Starter Active Member

    Dec 2, 2008
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    the datasheet is this one.... its Fairchild

    www.floka.com/cmos/pdf/4046.pdf

    i'm confused abt the input of the VCO.... the data sheet says that the VCO will oscillate at its free running freq if there isnt any input.... page 11 2nd row
     
  4. kahafeez

    Thread Starter Active Member

    Dec 2, 2008
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    while at page 7 fig 5 it says that VCOin= Vdd/2....

    its confusing me.... also tell me that what does this means that the C1 should be greater than 50pF.... actually values in nano are greater bt they may also mean like 100pF.... :-?
     
  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Page 11 is for a closed loop with the phase comparator connected.
    For capacitor values :
    1000 pF = 1 nF
    1000 nF = 1 μF

    Greetings,
    Bertus

    PS please write out the words completely, it becomes hard to understand with your "shorthand"writing.
     
  6. kahafeez

    Thread Starter Active Member

    Dec 2, 2008
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    Bertus thanks for replying but i couldnt really get what you are saying.....

    did you see the picture i attached? do you think it would work to get a free running frequency of 0.8MHz.... like do you think the connections are ok or do i need to make some changes.....
     
  7. kahafeez

    Thread Starter Active Member

    Dec 2, 2008
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    i got your comparator part but whats greater than 50pF, 100pF or 100nF.... and could you please help me with setting the lock range and the capture range....

    i used NE565.... which has really easy formulae.... but this one isnt that simple..... but as NE565 only has the free running of 500KHz it wasnt well enough for me..... my ultimate goal is to use 74HC4046 which has the free running of about 17MHz but i thought it would be better if i work with CD4046 first....


    what do you think the FSK signal's freq will be if the VCO is set at 0.8MHz and the VCOin is a 0 to 5V square wave at VDD =10V
     
  8. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    When I look at the diagram, I think you should have C1 = 56 pF and R1 = 10 K and R2 = not used.

    Greetings,
    Bertus
     
  9. kahafeez

    Thread Starter Active Member

    Dec 2, 2008
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    thanks dude..... thanks for helping me out..... i'll goto the lab tomorrow.... work there and then post the results.... i'll also put a square wave at the vco in.... find the two freq then post here to find out the cap range and the lock range..... thanks once again bro.... i couldnt find someone here to help me about this

    just tell me one more thing..... the output of the VCO would be a sine or a square.......
     
  10. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The output of the VCO will be a block voltage of about 10 Volts (you are using 10 Volt power supply).

    Greetings,
    Bertus
     
  11. kahafeez

    Thread Starter Active Member

    Dec 2, 2008
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    block voltage ???? you mean like a clipped sine wave which is somewhat like a square wave??
     
  12. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The out put of the VCO is a real squarewave, it can be fed directly or through a didiver to the phase comparator.

    Greetings,
    Bertus

    PS attached the datasheet from Philips
     
  13. kahafeez

    Thread Starter Active Member

    Dec 2, 2008
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    oh, but i wanted to make a sine wave FSK signal...... what do i do then........
     
  14. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Some questions .
    What is the purpose of your FSK signal ?
    What frequencies do you want for the FSK signal ?
    What is the datarate ?
    Why do you want the FSK signal to be sinewave ?

    Greetings,
    Bertus
     
  15. Audioguru

    New Member

    Dec 20, 2007
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    896
    The CD4046 is a Cmos logic IC. The unused inputs must never be open, they must be connected high or low. The VCO input controls the frequency by its voltage and leaving it disconnected ruins the oscillator.
     
  16. kahafeez

    Thread Starter Active Member

    Dec 2, 2008
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    hi folks, i tried this configuration and it worked.... see the images....


    no i've one question..... as i have to make an FSK signal so i'd like to give an input which is a square wave of 300bps..... where do i give that square wave? if i give it at the VCO in pin the wave goes down from 625KHz to 1KHz :(


    1. i've to send data into air using this FSK signal.

    2. i want to keep my FSK's freq as high as possible so that i can reduce the antenna size....

    3. i can set the datarate at different levels.... it can be 300bps, 1200bps, 4800bps or even 9600bps.... i'm taking that square wave from the UART of an 89C51 microcontroller....

    4. i want it to be a sine wave just because in theory we've seen the FSK of sine shape.... its not really imp to convert it to a sine wave bt if its easy then i'll do it.....


    PS: i'm not concerned with wat the standards are fro wireless comm... like what freq am i using as there isnt any check in my country..... and i also wont keep the range more than 100m
     
  17. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Do you have a licence to transmit at the frequency you want ?

    You could even use a 555 to create a fsk signal.
    When you put a signal at pin 5 (with a resistor of 4k7 in line) of the 555 it will change ther frequency.
    The signal will be squarewave, but when you take the signal of the timing capacitor via a high impedance buffer, it will be triangle.
    Filtering (lowpass) the triangle will give a alsmost sine shape.

    Greetings,
    Bertus
     
  18. kahafeez

    Thread Starter Active Member

    Dec 2, 2008
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    sir i told u i dont care abt the license.... and i want to keep the freq as high as possible.... in a few MHz.... 555 wont do that..... so can u plz tell me where should i put the square wave to get an FSK signal.... i dont care abt the shape too now.... square triangle or what ever....
     
  19. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    If you do not care about a licence I will not help you anymore.
    I am a licenced radio amateur and it is illegal to use some frequencies.

    Greetings,
    Bertus
     
  20. kahafeez

    Thread Starter Active Member

    Dec 2, 2008
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    ok sir.... i'll use from 13.553MHz to 13.567MHz..... this is from the ISM band

    http://en.wikipedia.org/wiki/ISM_band


    this is a part of my final year project and i wont keep the range long.... it would be around 50m or so..... the rules abt using freq arent so strict in my country....
     
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