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5 Mhz crystal in the UK — Parallax Forums

5 Mhz crystal in the UK

Paul MPaul M Posts: 95
edited 2008-07-31 18:57 in Propeller 1
Why is it so hard to buy a 5 MHz crystal here in the UK?
RS don't have a single 5MHz crystal as far as I can see.
Farnell can supply one in the large HC49U case style but you have to order from the US for the small HC49US case style.·The £15.95 handling charge makes a £0.20 crystal quite pricey!
I also wanted a small SMT variant to go with a LQFN PCB design but I can't find these either.

Anyone help?

Comments

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2008-07-30 16:18
    Paul,

    You won't find a small SMT 5 MHz crystal anywhere. I've looked, and they just don't exist. Apparently, the resonant element at that low a frequency has to have a certain minimum size. (I'm sure size is one reason Parallax uses a 10 MHz crystal, instead, on their Spin Stamp.)

    One thing you might consider is a cylindrical can-style crystal. They're a bit fragile but keep a low profile when bent over horizontally. Some come in a bent-lead SMT configuration that may prove adequate if you also solder the can to the board.

    -Phil

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  • cheapskatecheapskate Posts: 6
    edited 2008-07-30 16:27
    Maplin have stock in HC-49/U can.
    Maplin P/no RR79L
  • LeonLeon Posts: 7,620
    edited 2008-07-30 16:39
    I bought some from Rapid Electronics: Order code 90-0460

    Leon

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  • Paul MPaul M Posts: 95
    edited 2008-07-30 16:39
    @cheapskate

    Farnell also do the 'large' case version. I would like the lower profile HC49US as comes on the parallax protoboard

    @Phil

    Yes, I understood this when I looked at the size of another SMD crystal.·Probably why·some companies produce a SMT variant which is just the HC49US version with the pins bent·thru 90 degrees(plus an insulator)
  • Paul MPaul M Posts: 95
    edited 2008-07-30 16:42
    Leon

    Didn't try Rapid must admit - I don't buy a lot from them as finding anything in their online catalogue is a real pain. Their webste is unavaialble at the moment but I'll try later
  • cheapskatecheapskate Posts: 6
    edited 2008-07-30 16:46
    Why use a 5Mhz crystal, unless you have a reason for this exact frequency. According to page 180 of the propeller manual, _clkmode allows most crystals between 4mhz & 80Mhz to be used and within limits a PLL multiplier. (thats if I understand this correctly!! ).


    Rapid Electronics used to do 5Mhz in HC49/U. There web site down for maintenance so unable to confirm this
  • LeonLeon Posts: 7,620
    edited 2008-07-30 16:50
    ACT makes the ones that Rapid sells. They make a couple of small surface-mount ones:


    http://www.actcrystals.com/

    Leon

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle
  • Mike GreenMike Green Posts: 23,101
    edited 2008-07-30 16:51
    The datasheet indicates that a crystal between 4 and 8MHz can be used if the PLL is to be used. You can use other crystal frequencies (in fundamental mode ... not in overtone mode) if you are not using the PLL. Obviously, people (including Parallax) are using crystals outside that range (like 10MHz), but that's outside specifications for the full temperature and supply voltage range.
  • hinvhinv Posts: 1,255
    edited 2008-07-31 18:30
    The Prop Dongle uses a 5MHz surface mount crystal.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2008-07-31 18:57
    hinv said...
    The Prop Dongle uses a 5MHz surface mount crystal.
    Yes, but it's an HC49/US, not a compact SMD device. In fact, this particular package actually takes up more board space than the equivalent thru-hole part, due to the pads extending beyond the can perimeter.

    -Phil

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    'Still some PropSTICK Kit bare PCBs left!
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