timer with xtal

Discussion in 'General Electronics Chat' started by Marcusb, Jun 14, 2004.

  1. Marcusb

    Thread Starter New Member

    Jan 19, 2004
    9
    0
    watches and RTC's use a 32.768 Khz crystal to achieve a one second interval using a divider.

    How do they get 100ths of a second? I want to time something with a microcontroller but don't know how to get an accurate clock source for .01 sec.

    Marc
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi

    Cheat. Get a TTL oscillator that puts out a frequency that divides easily, like 100 KHz or 1 MHZ. There's no rule about acheiving timing through 32 KHz xtals. A TTL oscillator is easier to use, besides.
     
  3. Marcusb

    Thread Starter New Member

    Jan 19, 2004
    9
    0
    Thanks beenthere. I'm still somewhat of a newbie and didn't think outside the crystal box. I'm still curious as to how a watch with a 32khz crystal provides and 100ths stopwatch feature.

    Anybody know?

    Thanks,

    Marc
     
  4. bodhisatva

    Member

    May 20, 2004
    23
    0
    May be you are confused becouse the frequency deviders usually devide on power of 2? But you can design a programable devider and get a frequency devided on 3 or 13 or 10 for example. I have seen a simple circuit of frequency devider with a pot for adjusting the coeff. of devision. It act's as a monostable generator. So you have many choises.
    By the way how you come to the MCU?
    You should pass more simple stages of digital electronics:)))

    Good luck!
     
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