Hey all, i am trying to build a digital stop watch with TAmega168. So I am wondering what crystal oscillator should i be using? I know that a 16MHz will not work, because it doesn't divide even to one second.

Thanks in advance!!

 

You could use an I2C real-time clock chip running on a 32,768 Hertz crystal.

hgmjr

 

For example: DS1307

hgmjr

 

Hello,

When you take a 3.2768 Mhz crystal and divide this by 32768 , you will end up with 100 Hz ( 0.01 sec ).

More you can find in the "crystal design notes"
http://www.foxonline.com/pdfs/xtaldesignnotes.pdf

This link comes from this page on crystal oscillators.
http://www.educypedia.be/electronics/analogoscicrystal.htm

Greetings,
Bertus

 

For example: DS1307

hgmjr

You would connect this chip up to the 2-wire interface (TWI) on the ATMEGA168.

hgmjr

 

Use the 16-bit timer and the prescaler on the mega168 to get your 1Hz signal while using a crystal that divides evenly by the prescaler:
4, 8, and 16 MHz all work. The 32.768 kHz crystal also works with the 8-bit T0 or T2

Also use the CTC or PWM modes so the mega168 auto-reloads the timer.

 

Use the 16-bit timer and the prescaler on the mega168 to get your 1Hz signal while using a crystal that divides evenly by the prescaler:
4, 8, and 16 MHz all work. The 32.768 kHz crystal also works with the 8-bit T0 or T2

Also use the CTC or PWM modes so the mega168 auto-reloads the timer.

are you saying that 16Mhz, 4Mhz and 8Mhz clock will also works for digital stop watch? but they don't divide evenly with 2^X to get 1 Hz.

Thanks

 

You could use Timer 1 in CTC mode and set OCRA1 = 0xf424 and the prescaler to 256 if you are using a 16MHz crystal. This is the clear timer on compare match mode which you set a value and the timer will count to that value then reload automagically while triggering an interrupt