+ Reply to Thread
Results 1 to 11 of 11
  1. #1
    Join Date
    Aug 2006
    Location
    SWITZERLAND (french part)
    Posts
    572

    Default Check oscillator/Xtal accuracy - how to?

    Hi,

    What is the best way to check the oscillator's or the Xtal's accuracy?


    Hi, we are pleased to see that you are using our forum.

    We'd like you to become a member of our community. Membership is FREE, please REGISTER and view our forums without these annoying reminders!

    Once registered you may post on the forums, download from the file areas and use the WIKI without interruption.






    Setting a Pin HIGH then LOW and startover again seems clearly not a good way of doing.
    Roger

  2. #2
    Join Date
    May 2004
    Location
    Le Treport 76 FRANCE
    Posts
    3,339

    Wink Flotul is Back !!!

    Hello, Roger

    Last time I did that ( 15 days ago ...)

    I used my R/C Transmitter ( 1500s neutral )... and placed a "PULSIN" command at the other end ...

    Result Was OscTune +6 and +9 @ 4 Mhz, for a couple of 16F88 in Int RC mode.

    You also can use a DIL canned Oscillator and a gang of dividers ( 4040 ??? ) to get a "readable" signal period.

    Alain
    Last edited by Acetronics; - 4th March 2009 at 13:28.
    ************************************************** ***********************
    Why insist on using 32 Bits when you're not even able to deal with the first 8 ones ??? ehhhhhh ...
    ************************************************** ***********************
    IF there is the word "Problem" in your question ...
    certainly the answer is " RTFM " or " RTFDataSheet " !!!
    *****************************************

  3. #3
    Join Date
    Jul 2003
    Posts
    2,358

    Default

    Frequency Counter! They're cheaper than a round of drinks at the pub nowadays... (even some DVM's go to 10MHz) but don't connect directly (it'll load the oscillator)... a couple of turns of enamelled copper wire around a small jar fed back with some coax to the Frequency Counter is enough to pick up a signal.

    If you must connect, always do it on OSC2 which is the drive-out pin.

  4. #4
    Join Date
    Aug 2006
    Location
    SWITZERLAND (french part)
    Posts
    572

    Default ...

    Connecting an oscilloscope directly to the resonator or Xtal will allow me to check the oscillator only.

    To make a nice and clean measurement of the PIC itself allowing me to fine tune it (OSCTUNE register), how should I do?
    Roger

  5. #5

    Default

    For the internal osc, just set your config option to output Fosc/4 on OSC2 and check it
    with a freq counter or O-scope.

    With a 4MHz internal osc, you should see a 1MHz output on OSC2 when it's spot-on 4MHz.
    Regards,

    -Bruce
    tech at rentron.com
    http://www.rentron.com

  6. #6
    Join Date
    Aug 2006
    Location
    SWITZERLAND (french part)
    Posts
    572

    Default external?

    Thanks Bruce,

    What about measuring the PIC's accuracy with an Xtal?
    Roger

  7. #7

    Default

    Well, since the PICs accuracy is totally dependent on the external crystals accuracy, I
    would suggest you look into what Melanie posted above...;o}

    A freq counter will do the trick as long as you're not loading the oscillator.

    If Melanie says it works, you can normally take that to the bank, and be done with it.

    She knows her stuff..;o}
    Last edited by Bruce; - 4th March 2009 at 19:39.
    Regards,

    -Bruce
    tech at rentron.com
    http://www.rentron.com

  8. #8
    Join Date
    Aug 2006
    Location
    SWITZERLAND (french part)
    Posts
    572

    Default Humm...

    So I'm going to take Melanie's advice as the "absolute" truth.

    As you say Bruce, what Melanie says, it is!

    Thanks All.
    Roger

  9. #9

    Default

    I wouldn't take anything anyone says here as the "absolute" truth, but my
    money would be on whatever Melanie said unless I was 100% sure I could prove
    it was otherwise..;o}

    And good luck with that!
    Regards,

    -Bruce
    tech at rentron.com
    http://www.rentron.com

  10. #10
    Join Date
    Jul 2003
    Location
    Colorado Springs
    Posts
    4,935

    Default

    If you don't happen to have a frequency counter.
    You can put a 32768hz watch crystal or DS32KHZ compensated oscillator on TIMER1 and use it as the time base to measure your system frequency.

    I trust it more than frequency counters, which in the Mhz ranges can be off by several Khz, depending on the quality of the counter.

    An example of the technique can be found in Microchip's AN244.
    Although it's geared towards calibrating the internal oscillator, the concept is the same for externals.

    http://www.microchip.com/stellent/id...pnote=en012071
    DT

  11. #11
    Join Date
    Aug 2006
    Location
    SWITZERLAND (french part)
    Posts
    572

    Default

    Thank you Darrel.

    I should have started searching there... Lots of infos to find in the application notes ;-)
    Roger

Similar Threads

  1. HARDWARE I2C SAMPLE CODE question
    By Michael Wakileh in forum Code Examples
    Replies: 2
    Last Post: - 16th June 2009, 21:07
  2. PIC16F877A - Timer0 won't interrupt
    By WishMaster^ in forum mel PIC BASIC Pro
    Replies: 19
    Last Post: - 25th April 2007, 08:25
  3. Code check -- button not working
    By docwisdom in forum mel PIC BASIC Pro
    Replies: 12
    Last Post: - 2nd March 2006, 23:43
  4. Block Check on Serial Comms.
    By Mark Scotford in forum mel PIC BASIC Pro
    Replies: 4
    Last Post: - 15th June 2005, 09:27
  5. Even Parity Check, How?
    By Mark Scotford in forum mel PIC BASIC Pro
    Replies: 1
    Last Post: - 24th January 2005, 10:21

Members who have read this thread : 0

You do not have permission to view the list of names.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts