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Is this XTAL Ok to use with Propeller? — Parallax Forums

Is this XTAL Ok to use with Propeller?

DavidMDavidM Posts: 630
edited 2008-03-02 11:06 in Propeller 1
Hi,

Is this xtal OK to use with the Propeller ( I need low height through-hole )

MOUSER PART NO: 520-HCU500-S

HC-49/U-S Microprocessor Crystals 5MHz 30ppm

regards


Dave M

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2008-03-01 04:06
    It looks like it ought to work except for the load capacitance. The XTAL1 setting of the Propeller is intended for crystals in this frequency range and that has a load capacitance of about 36pF. When the crystal is made for a different load capacitance like this one, it will oscillate, but the frequency will be a little off. For most uses, that won't matter much. If you plan to use the Propeller for timekeeping, you'll need to account for this.
  • DavidMDavidM Posts: 630
    edited 2008-03-01 04:22
    Thanks Mike,


    Yes, I do need to do time keeping in some of my projects,
    So could you recommend a different xtal from MOUSER? as I am placing an order with them and I would like to get some xtals,


    I am not sure ( apart from the frequency) what to look out for.

    It need to be through hole.
    regards

    Dave M
  • Mike GreenMike Green Posts: 23,101
    edited 2008-03-01 04:44
    The "ECS-50-20-1X 5.0", Mouser # 520-HCA500-20X will work better although its load capacitance is 20pF. You'll get a bit closer using the XTAL2 clock setting. Like I said, crystals are made for use in a particular circuit and they will have the specified frequency in that circuit. When you use a circuit with a higher or lower load capacitance or the temperature is different than that specified, the crystal frequency will be a little different from what's stamped on the case. Operating temperature is by far the greatest factor and, if you want an accurate system clock, you'll need to use a temperature compensated crystal oscillator.
  • DavidMDavidM Posts: 630
    edited 2008-03-01 05:17
    HI Mike,

    So better yet, What is the SPEC for the xtal used say in the propeller demo board? I can't see this anywhere


    Regards

    Dave M
  • LeonLeon Posts: 7,620
    edited 2008-03-01 12:45
    Perhaps a tunable series inductor could be used to get the frequency 'spot-on', with a given crystal, if the frequency is too low. A capacitor could be used if the frequency is too high. The temperature stability will be affected, of course.

    Leon

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle
  • Paul BakerPaul Baker Posts: 6,351
    edited 2008-03-01 23:22
    DavidM said...
    HI Mike,

    So better yet, What is the SPEC for the xtal used say in the propeller demo board? I can't see this anywhere


    Regards

    Dave M
    The information is in·the manual (p29)

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Paul Baker
    Propeller Applications Engineer

    Parallax, Inc.
  • DavidMDavidM Posts: 630
    edited 2008-03-02 09:26
    Hi Paul,

    Thanks for that, but that page just confused me more :-( !!!!

    I just needed to know the manufacturers part no of the xtal that is used on the propeller development board.

    I had a look at the Parallax store and the spec for the XTAL is 20PF So I found a MOUSER Item that suits this , but they are a out of stock!

    MOUSER No: - 520-HCU500-20X

    regards


    Dave M.
  • LeonLeon Posts: 7,620
    edited 2008-03-02 09:51
    Try Digi-Key. They are difficult to find, most 5 MHz crystals have a 30 pF load. I just used one of those.

    Leon

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle

    Post Edited (Leon) : 3/2/2008 9:57:52 AM GMT
  • deSilvadeSilva Posts: 2,967
    edited 2008-03-02 11:06
    During the last months I used 12 to 15 different sorts of crystals (4.4 MHz to 12 MHz) with the Propellers; HC 49 as well as HC 18, mostly low cost versions (40 Cents). None of them failed!
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