Recommendation of clock signal type needed

Discussion in 'General Electronics Chat' started by hunterage2000, Jan 26, 2013.

  1. hunterage2000

    Thread Starter Active Member

    May 2, 2010
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    Hi all,

    So far for all the circuits I have built, I have used a 555 timer in astable mode as a clock signal. When I open up an electronic device such as a PC or Xbox I see the oblong shaped 2-pin oscillators. I want to know:

    Are these crystal oscillators?
    How are they connected and with what components?
    Are these the best type of oscillator to use as a devices main clock signal?
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    If you mean these or these, they are crysals and are a part of a crystal oscillator circuit. The main advantage compared to an RC oscillator like with a 555 is that the frrequency is much more stable. They are usually connected right to the the chip that needs them, along with two small load capacitors.
     
  3. ScottWang

    Moderator

    Aug 23, 2012
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    Last edited: Jan 26, 2013
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  4. takao21203

    Distinguished Member

    Apr 28, 2012
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    Something like this.

    Normally you would use a small microcontroller when you want a crystal.
    Getting it right for a 32 KHz crystal is not so easy. And the drive capability is poor. Why all the effort? Small controllers are cheap.

    Who really wants a NE555 crystal osc., takes 10mA for nothing.

    The right thing for a 32 KHz crystal is not a logic gate or NE555, but a PIC16F54.

    I don't have the schematic for the 32 KHz crystal. These on the internet don't actually work. The amplitude is too low, or they don't work at all.
     
  5. crutschow

    Expert

    Mar 14, 2008
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    32 kHz crystals are typically used for watch circuits or other timekeeping circuits, not microprocessors (although they can be for low power requirements, but the processor will run very slowly).
     
  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Another option is to get a crystal oscillator package, which is rectangular with 4 pins:

    These have the capacitors and buffer amplifier built in.

    [​IMG]
     
  7. ScottWang

    Moderator

    Aug 23, 2012
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    I got three crystal oscillator modules from old PC main board, and I put them on a PCB used a 4 pins DIP sw to switch that which module will be the output, and added a 74HC4040 to divide the frequency, it become an easy way to get a stable clock generator.

    Crystal osciilator modules : 24Mhz,32Mhz,40Mhz.
     
    Last edited: Jan 27, 2013
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  8. ScottWang

    Moderator

    Aug 23, 2012
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    Here is the 1Hz time base using CD4060 and CD4027 from 32768Hz, I haven't try this yet.

    [​IMG]


    The below circuit that I used for a several years, normally use is ok, if you want to use it to more precisely then you need to adjust the capacitors.
    [​IMG]
     
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  9. takao21203

    Distinguished Member

    Apr 28, 2012
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    Yes but it is IC based. 2 transistors are enough! The IC in my picture is only to divide, and drive a small speaker (for testing).

    The 4060 is a special time base IC.

    4 MHz crystals can work with only 1 digital MOSFET. But not really a good circuit :) I do not use it.

    I have one weird 19 KHz crystal here, never tried to build a circuit. From a VCR.
     
  10. ScottWang

    Moderator

    Aug 23, 2012
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    Transistor crystal oscillator is the circuit base, it used in RF transmitter very often, I didn't use it in the digital circuit, the fact is that I'm lazy to solder too many pin as resistors and transistors, if I can use IC that is more easier.

    I used 4Mhz crystal with 74LS04 to generate the frequency for my 9.9Mhz frequency counter, 4Mhz divided by some CD4518 to be the 1Hz timebase.

    The timebase should be adjust, but i didn't, someday, I used my 9.9Mhz frequency counter comparing with 500Mhz frequency counter, testing under 10Khz is very correct, but when I increasing the frequency to 20Khz, my F-counter will appearing 2Hz error, it means that it will increasing 2Hz when the input frequency increasing 10Khz.

    The timebase of the 500Mhz F_counter was generated by 10Mhz.
     
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