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User avatar
By roach
#11666
I'm trying to work an AVR into my design, and want to use a 16MHz external clock source on XTAL. There are a couple of attractive, small, SMT ceramic resonators with built in load capacitance that I'd like to use, but the datasheet recommends a crystal. Is it safe to go with a ceramic resonator? If not, why not? What's the difference between the two?
User avatar
By leon_heller
#11671
You may use either. The crystal gives a more accurate frequency and will be more stable with temperature changes and over time.

Leon
By beebop
#11674
Hi Roach,

I just wanted to add my two cents, er...

If you are just making one, or a few of this, then spend the extra few cents, and get the best. The amount of money you will save using the resonator won't really add up unless you are mass producing this board. Like Leon said, the crystal is more accurate, and more stable.

I don't know, I usually spring the extra little bit for the higher end part. It wouldn't make sense, for the small number of pieces I will ever produce, to use a cheaper part. Yes, the resonator is easier to wire up, but in the long run, especially if you have serial comms in mind, you will be glad you spent the extra little bit.

Regards,
Robert
User avatar
By roach
#11675
It's not really a question of money, more a question of PCB space. The resonator is a smaller, surface-mount part, with built-in capacitors.

This is for a motor-controller board, with an L298 and on-board ldo regulator. The board should handle up to 40V, with a maximum motor draw of 4A, so there is definitely the possibility of heat building up on the board. I guess I'll go with the crystal.

Thanks guys!
By SOI_Sentinel
#11681
One thing you will notice, though: if this thing is meant to be in a high G shock environment or EXTREME temperature ranges, the resonator is rated higher. Even RC aircraft don't count as that high unless you're either going to intentionally crash it multiple times or place the unit on top of a hot main (not servo) motor.
User avatar
By roach
#11690
SOI_Sentinel wrote:One thing you will notice, though: if this thing is meant to be in a high G shock environment or EXTREME temperature ranges, the resonator is rated higher.
If this thing goes into "high-G" mode (ie: dropped from the rooftop), the crystal will be the least of my worries. I anticipate temperatures should not go over about 85C, since that's the maximum optimal temp range for various other components on the board. If it does, I'll work in a heat sink/fan. Looks like Crystal is the way to go. Now if I can only find one small enough...
By SOI_Sentinel
#11694
Sparkfun's isn't small enough? (yes, I know you still need a few more components)

http://www.sparkfun.com/commerce/produc ... ucts_id=94
User avatar
By roach
#14991
Wow. Actually, this is the perfect size. Thanks for pointing me in the right direction! Only problem is, the project's changed since then. Now I need a 8 MHz (which doesn't come in this package), and a 12.288 MHz (ditto). Oh, well...
User avatar
By roach
#14999
BTW: Turns out NewarkInOne stocks these in smaller quanitites (DigiKey only sells them in lots of 1000).

Edit: and Mouser...