How can I divide the frequency

Discussion in 'General Electronics Chat' started by peterlan, Sep 13, 2008.

  1. peterlan

    peterlan Thread Starter New Member

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    Hello everybody, I am doing a project on building a digital clock. Now I have the crystal oscillator 4Mhz already. I would like to know how to divide the frequency to 1 hz since the clock of the digital clock need to be 1 Hz. Anyone who has some idea plz tell me?
    PS. I have found some IC's that can divide the frequency ;74HC390 which can divide up to 100 but i still dont know how it work.Moreover I've found some circuit like this
    http://www.elecfree.com/electronic/xtal-oscillator-frequency-by-74ls04/ .


    Thank you in advance
    Pete
  2. hgmjr

    hgmjr Moderator Staff Member

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    Ordinarily, if you don't intend to achieve a resolution below 1 second, you would start with a much lower frequency oscillator. 32,768 Hertz seems to be a popular starting frequency. The crystals that are available at this frequency abound. The nice part about starting with this frequency since it is equal to 2 raised to the seventh power is that it is easily divided down using a commonly available counter IC.

    hgmjr
  3. peterlan

    peterlan Thread Starter New Member

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    :)Thank you for your advise, However, i still want to know how can it be done?
  4. hgmjr

    hgmjr Moderator Staff Member

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    A frequently used IC for this purpose is the CD4040 which is a 12-bit counter/divider.

    hgmjr
  5. peterlan

    peterlan Thread Starter New Member

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    Furthermore, hgmjr
    Can I use the real time's DS1007 just like you suggest a guy to do a stop watch
  6. hgmjr

    hgmjr Moderator Staff Member

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    I think the DS1007 is a silicon delay line.

    Did you perhaps mean a DS1307?

    hgmjr
  7. peterlan

    peterlan Thread Starter New Member

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    Yep I type it wrong
  8. hgmjr

    hgmjr Moderator Staff Member

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    You can use a DS1307 but then you would need a microcontroller to set it up using the I2C interface.

    I got the impression from your initial post in this thread that you were looking for a non-microcontroller based digital clock design.

    hgmjr
  9. SgtWookie

    SgtWookie Expert

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    I believe you meant to refer to the CD4060, as it's better suited for operating with a crystal. It has 14 divider stages instead of 12.

    OnSemi has better documentation on their MC14060B, an equivalent to the CD4060B: http://www.onsemi.com/pub/Collateral/MC14060-D.PDF
  10. hgmjr

    hgmjr Moderator Staff Member

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    The 4060 may well be a better choice under the circumstances.

    Thanks,
    hgmjr
  11. nanovate

    nanovate Well-Known Member

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    If the OP can use a microcontroller then the division would be a simple programming task.
  12. SgtWookie

    SgtWookie Expert

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    I agree, a microcontroller would be the way to go.

    However, if the OP insists on using a 4MHz frequency source, the attached divider circuit would get them down to 1kHz, or 1/1000 of a second clock increments. Adding another pair of 4518 stages would get them down to 1/10 second.

    If they're using a crystal, the AND gate could be replaced with a 4093 quad Schmitt-trigger NAND; use two as the crystal driver & buffer, and two to build the functionality of the AND gate.

    Attached Files:

  13. hgmjr

    hgmjr Moderator Staff Member

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    I too agree that a microcontroller would be the way to go.

    The added flexibility and additional functionality could prove very valuable in the end.

    hgmjr
  14. peterlan

    peterlan Thread Starter New Member

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    thx verymuch for every body for any suggestion. Actually,I also want to use the microcontroller but I don't have the knowledge on that much and I think I have only one week to do this project. However, i really thanks for every suggestion .

    Ah I have a question Depend on this
    "the attached divider circuit would get them down to 1kHz, or 1/1000 of a second clock increments. Adding another pair of 4518 stages would get them down to 1/10 second.

    If they're using a crystal, the AND gate could be replaced with a 4093 quad Schmitt-trigger NAND; use two as the crystal driver & buffer, and two to build the functionality of the AND gate."

    If I do according to the attached i'll get the clock as 1/10 second , I need to divide by 10 another time right? Or not?
  15. hgmjr

    hgmjr Moderator Staff Member

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    Since your target frequency is 1 Hertz you will need the additional dividers to get there.

    If your interest is inclined toward microcontrollers, I would suggest that you make a commitment to become familiar with the subject as soon as it is convenient for you to do so.

    hgmjr
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