timer with xtal

Thread Starter

Marcusb

Joined Jan 19, 2004
9
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
 

beenthere

Joined Apr 20, 2004
15,819
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.
 

Thread Starter

Marcusb

Joined Jan 19, 2004
9
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
 

bodhisatva

Joined May 20, 2004
23
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!
 
Top