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Crystal osc tester

Discussion in 'General Electronics Chat' started by be80be, Nov 16, 2017.

  1. be80be

    be80be Well-Known Member

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    I been looking for a simple way to test crystals I have them small can types . Is there a easy plug in circuit using any ideas would be helpful thanks
     
  2. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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  3. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    If you check on Banggood they do a cheap kit, it uses a PIC and places the crystal in an oscillator and measures it's frequency.

    I've never ordered one, as I have no need or use for it.
     
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  4. dave

    Dave New Member

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  5. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    If this question is related to your modeling, you will need more than the base operating frequency. I got interested in that about a year ago for filters and needed to do some characterizations. There is a lot on the Internet, including online calculators. Unfortunately, I neglected to copy links to the online calculators, but these links may help:

    http://www.w5dor.com/ladder_filter_w7zoi.pdf
    This link goes to Wes Hayward's original article: Wes Hayward, W7ZOI,” Refinements in Crystal Ladder Filter Design,” QEX, June 1995, pp 16-21.
    That is also published here: QRP Power, ARRL Publication No. 210

    https://www.arrl.org/files/file/QEX_Next_Issue/Nov-Dec_2009/QEX_Nov-Dec_09_Feature.pdf
    The above is a nice article by Horst Steder & Jack Hardcastle

    Edit:
    If it is just an oscillator, here is one I have used:
    upload_2017-11-17_5-28-13.png
    Source:
    http://www.fairchildsemi.com/an/AN/AN-118.pdf
    And if you look at the crystal oscillator circuit in any PIC datasheet, you will see a family resemblance.

    John
     
    Last edited: Nov 17, 2017
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  6. be80be

    be80be Well-Known Member

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    I no the circuit the thing is I got lot of unmarked ones guess I just wire something up.
    I was looked at google. i was just wanting to see what any of you used.
    jpanhalt ive not figured ho to make crystal out of cap for qucs cant find a crystal but im sure i will figure it out lol
     
  7. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    be80be
    In LTSpice, there is nothing to make. Crystals and capacitors are electronically the same. The only difference is a tarted up symbol for the crystal:

    upload_2017-11-17_10-12-11.png

    You select the same variables for either. I don't know in qucs whether you have the same choices for a capacitor. If you do, it will work for a crystal too. Unless you know the inductance and resistance values, you can do a lot of trial and mostly error before hitting on what works. That is where one of the online calculators might come in handy in addition to a representative datasheet.

    John
     
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  8. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    Crystals over 20mc usually operate at third or higher harmonics, if you get a frequency that seems odd it might be 1/3, 1/5, 1/7 or higher of its intended operation.
     
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  9. debe

    debe Active Member

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  10. Diver300

    Diver300 Well-Known Member

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    An oscillator based on an inverter is the easiest one to use for most crystals. Putting a resistance of a few kΩ in parallel with the inverter, and having the series resistance very low or shorted will encourage overtone oscillation.

    You need very specialist equipment to work out whether a crystal is supposed to be a fundamental or an overtone, but the frequency it runs at will usually give you an indication, as the crystal will be adjusted to expected mode. The 3rd overtone isn't exactly 3 times the fundamental, but it will be a few hundred ppm (parts per million) different. So a crystal that runs at 10.0024 MHz or 30.00006 MHz will most likely be designed to run at 30 MHz
     
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