AVR-Chat

On Mon, 12 Dec 2005, Robert Payne wrote:

> Hi All,
> 
> I'm trying to get a RTC going on a Mega 8 using a 32 kc watch crystal
> as per Atmel app note AVR134.
> 
> The code works well except that the time gains about 3 seconds per hour.
> 
> The crystal is a surplus watch crystal  that I had and I have no idea of
> the capacitance
> load that it requires.
> 
[snip]
> Do I need a 6pf or 10pf crystal?
> 
> Do I need any extra caps to gnd, not using any at the moment, would a
> small trimmer help?
> 
> Many thanks,
> 
> Rob Payne
> 

Hi Rob,

I've never used a watch crystal but I have used crystals in the MHz range.  
Best bet is a trimmer capacitor to set the frequency exactly to what you 
want it to be.

Zack