Crystal selection??

Guest · Posted: Fri Jan 26, 2007 11:16 am

Hi Guys,

I need to select some crystals (not oscillators or resonators) for my first PIC project. It is not clear to me whether I need a "series" load capacitance crystal, or a "20.0 pf" load capacitance crystal. I'm looking at some ECS through-hole quartz crystals in the Digikey catalog. Also, I'd like to use a low profile crystal, such as in the HC-49US package. The tolerance on this crystal is +/- 300ppm vs. +/- 30 ppm for the full-height version. Is this tolerance acceptable for indoor, reasonably temperature stable designs?

Thanks,

Chuck

kender · Joined: 09 Aug 2004 Posts: 768 Location: Silicon Valley

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

You should always use parallel resonant crystals with PICs.
(Never use the series type). Parallel resonant crystals will have
the load capacitance specified. E.g., 18pf, 20pf, etc. That's how
you can tell the crystal is parallel resonant.

We use the HC-49/US package or the surface mount version of it
(CSM-7) on 90% of our products.

There is no problem with the HC-49/US package. It's the most
popular type (even though it's through-hole). It's the cheapest
package. Look at any motherboard in a PC. For example, the
Via Mini-ITX board on my side bench has five of the HC-49/US
crystals on it.