Need 20Mhz crystal for Basic Stamp 2

Seattlerandy

Can I replace the 20Mhz resonator with a crystal and get better clock accuracy ?
What crystal part number ? Don't see it on the Parallex site. Any other mods to the board needed ?
thanks
Randy

Mike Green

You could replace the resonator with a crystal, but you're on your own in figuring out what crystal to use. Start with the datasheet for the PIC16F57 which is used in the BS2 and look at the suggested crystal characteristics. You may need capacitors for the crystal. The resonator has them built-in and the crystal does not. You won't be able to just substitute a crystal for the resonator on the BS2 module. There's not enough room. There'll be more room on the OEM board.

The better clock accuracy won't do you much good. There's no way to reference it directly. PAUSEs are already pretty good and the resonator is good enough for serial I/O. For timing most events, the statement execution time provides enough delay so that timing events is problematic. Other than "because it's there", is there a particular reason why you'd want to do this? If you want to time things accurately, how about using an SX or Propeller instead?

Leon

Crystals on PICs require feedback capacitors. It will probably oscillate OK without them, but the frequency will be wrong.

Seattlerandy

Thanks for info. I will repost if I have any luck with this. I want to make a timer for an event every day at the same time. Over 10's or hundreds of days the ol resonator will be way off.
Very cute little chip however working like a champ...

Franklin

I'd recommend an RTC if you want that kind of accuracy.http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/clock/List/0/SortField/4/ProductID/233/Default.aspx