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Author Topic: Part# for: 16 MHz crystal oscillator  (Read 5656 times)
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Does anyone know the manufacturer and part# for the 16 MHz crystal oscillator that comes on the Diecimila?
The number on the part is "S16B00L6", but I can't find a data sheet using that...
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I thought it was just a generic crystal. Nothing special.
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Unfortunately, there are several types of "generic crystal."  The consequences of using the wrong type are usually small, but detectable, and an actual part number would be a good idea.
(we once ("in the dawn of the internet") shipped some products with a series resonant crystal instead of the correct parallel resonant crystal on an Ethernet controller chip.  It generally worked fine, but a customer was able to detect the out-of-spec state.  Very embarrassing.)
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I need the data sheet to verify the operating temperature range... Generally, the crystal is one of the most sensitive parts on a board...  I could assume it's good to 70C (probably not good to 85C), but I rather not assume.

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Diecimila uses 22pF capacitors for the crystal, so you need a crystal that matches the capacitance specifications of 22pF.  I don't think the temperature specification is critical, unless you are placing the Diecimila inside a volcano or someplace really hot.
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Making my own pcbs the other day I had a hard time finding a 16hz xtal with parallel 22pF caps through mouser but I did find a 16mhz xtal and it specified in the paert description parallel 18pF caps so on a whim I went that way and just picked up some 18pF ceramic caps. It worked flawlessly. So my marginally educated opinion is that a xtal with 22pF caps isnt entirely mission critical. As long as the parts that are used match up (the xtal is used with the caps specified by the xtal) it should be ok.

B
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I think the reason why selecting capacitors is not as critical as other components, is because ceramic caps have a huge margin of tolerance, so usually replacing caps within a 100% range is considered a safe criteria... at least that is what I read the other day and I also used 22pf and 33pf caps with different crystals without any problems.
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So are the 22pF capacitors the Shunt Capacitance?  Or the Load Capacitance of the Crystal, also if the Arduino uses 2x 22pF in parallel, does that mean that the Shunt/Load capacitance of the crystal is 44pF?
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I think I answered my own question with a look on the wibble web.

The 22pF capacitors are the load capacitance (44pF because the caps are in parallel) that the crystal needs to oscillate at 16Mhz.  You have have other 16Mhz crystals that need require a different load capacitance, like FOXLF160-20 from http://foxonline.com/pdfs/hc49ulf.pdf.

Someone please correct me if I am wrong, I think this will greatly clear this post up.
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Actually, I think the caps appear in series WRT the relevant oscillation circuit...

Quote
You may have other 16Mhz crystals that need require a different load capacitance
My understanding of crystal/cap selection goes like this: "picking a correct crystal and capacitors for a particular micro is more complicated than most people think.  You can't just lay down a "generic" crystal and a couple of 22pF caps and expect everything to operating within the manufacturers specs.  You have to  know things about the particular crystal and its load capacitance, along with the inherent capacitance of the circuitry in the microcontroller and board traces, and probably you should pay attention to drive  levels too.   However, the typical consequences of doing it "not quite right" are either non-oscillation, or operating at a frequency slightly off specification.  Assuming the microcontroller operates at all (which means the crystal IS oscillating), it is probably operating close enough to the desired frequency that few applications will notice the difference.  So in theory, you can't just use a "generic" crystal circuit, but in practice, it almost always works anyway."

Microchip is supposed to have some good app notes on crystal selection and oscillator design.  I found:
 AN826 - Crystal Oscillator Basics and Crystal Selection for rfPIC™ and PICmicro® Devices
and AN849 - Basic PICmicro® Oscillator Design
Each goes into some detail on how the oscillator works, how you should pick caps and crystals, and how to tell whether it's working right.
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So I was partially right, but wrong in that the caps run in parallel (based on the second link westfw posted).  So the 16Mhz crystal that I posted; it would need 2x 26pF plus the 7pF Shunt capacitance for a 20pF load capacitance correct (based on the formula from the second link, pg4 i think)?  
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I prefer ceramic resonators with built-in caps. :-)
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But on pg 7 of the second link illustrates the problems with ceramic resonators compared to a crystal as an oscillator.  I doubt this would be a problem for most people's projects, myself included.
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Try: Citizen HC49/US.  In my quest to gather parts for an Arduino-on-a-Breadboard, I stumbled across this parts list, compiled by Tom Igoe.  Digi-Key part numbers are included for all Arduino components.  Here's Tom's tutorial on the ITP Physical Computing site for building an Arduino Breadboard, and here's the schematic from the Arduino site.
« Last Edit: May 04, 2008, 08:24:53 am by aerocapture » Logged

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Can i use this ?

Technical data:

Manufacturer: Abundance

Crystal HC49U 16.000.000Hz

-10 bis +60°C

Toleranz(25°C) +-30ppm

1,0mW
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Mein Arduino Projekte Blog:
http://ardu-megatank.blogspot.de/

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