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

 

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.

 

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

 

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!