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Topic: Crystal uses (compared to ceramic resonators) (Read 9 times) previous topic - next topic

spiffed

For virtually every resonator based board, someone comments "Will there be a crystal version" or "I'd buy it, but it uses a resonator".

So, why would you like a crystal? What would you use it for?
iDuino - MaxSerial - [url=http://spi

bens

In my opinion, a crystal is only useful if you want to have an extremely accurate real-time clock.  A resonator is more than adequate for most general timing purposes as its accuracy is typically something like 0.2 - 0.5%.

- Ben

spiffed

Ben, I agree with you 100% (which is why I make kits with resonators).

To be fair, the following illustrates the difference between resonators and crystals:






AWCR-16.00MDABL-16.000MHZ-B2
Price$0.18$0.27 (plus caps)
Tolerance0.5%0.05% (50ppm)
Temp Stability0.3%0.05% (50ppm)
10yr Stability0.3%0.05% (50ppm)


The worst case scenario (end of the temperature scale, 10+ years old, and worst sample) is about 1.1% (15.82MHz - 16.17MHz) while the crystal is about %0.15 (15.976MHz - 16.024MHz). Obviously you're unlikely to see this kind of error in either component. You'd have to look it up, but I believe NASA testing showed their resonators to be within 100ppm of the target frequency from the factory. It's also important to realize these numbers are based on a perfect board layout (and capacitor matching for the crystal, badly matched load caps can severely throw off the native frequency).
iDuino - MaxSerial - [url=http://spi

follower

The main reason I've seen given for using crystals is that the accuracy is required for stable serial communications.

--Phil.

ladyada

serial ports are designed to cope with 3%+ error with no problems

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