AVR-Chat

On Mon, 25 Sep 2006, Ralph Hilton wrote:

> On Mon, 25 Sep 2006 10:08:28 -0000 you wrote:
> 
> >Hi guys,
> >
> >I hope every thing is going OK.
> >I`ve question hoping somebody could provide me what I have to do.
> >How can I generate one second accurately to be applied Digital 
> >Clock ? by the way, I`ve tried by Timer/Counter0 , T/C Prescaler , 
> >Timer0 ovf0 (Int. Calling) but I didn`t get a real second .
> >
> >
> >
> >Plz help as soon as possible .
> 
> If you are using a crystal then there should be no problem getting a second by
> dividing down with a timer. If you are using the internal RC then you can't get an
> accurate second due to its lack of stability.
> --
> Ralph Hilton

You can also use an external crystal oscillator with a trimmer cap for 
frequency adjustment.  I've used a 10 MHz oscillator which I zero-beat 
with WWV here. If you have a known frequency standard like a rubidium 
standard handy, you can hook a scope up to the two outputs and adjust by 
Lissajous figures.

You can find 10 MHz OCXO's on eBay for $20 to $80.  I don't know how 
desperately you need the accuracy; that may be overkill.

The simpler solution would be to use the 1 pps output of a GPS engine, or 
use the 10 kHz output and divide it down.

Zack