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Author Topic: resonator vs crystal  (Read 3159 times)
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texas
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First off, it's not $15 normally, it's on sale.  My thank you pamphlet says that it was made under license by Smart Projects Italy.  How many fakes come in the blue box with the 6 stickers and the thank you pamphlet?  I haven't seen any yet.  If you look at the Smart Projects website you will see that it pretty much matches the site at GHEO electronics where the board is distributed from.
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texas
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I contacted trademark@arduino.cc and they said this:

   Thank you for the passion you have in Arduino, you put a lot of effort in investigations! Even micro center didn't realized they are not listed, we will add them immediately.
GHEO is the commercial entity that supplies micro center with the original made in Italy Arduino boards.


Thank you for your special attention on purchasing original Arduino branded products!


Ciao


So there you go, it's not a fake and it only costs $15 right now.
« Last Edit: February 22, 2013, 10:24:08 am by afremont » Logged

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texas
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The ad I saw online lists them as Gheo Electronics Arduino Unos.

According to the e-mail I got from Arduino, GHEO Electronics is authorized and so is Microcenter.
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The ad I saw online lists them as Gheo Electronics Arduino Unos.

According to the e-mail I got from Arduino, GHEO Electronics is authorized and so is Microcenter.

Good sleuthing! Good price too.
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The ad I saw online lists them as Gheo Electronics Arduino Unos.

According to the e-mail I got from Arduino, GHEO Electronics is authorized and so is Microcenter.

Well then congratulations for finding and sharing a very fine deal on a Uno R3 for $15, that is an amazing price. You have to understand our prior skepticism as the web is saturated with Uno clones masquerading as the real deal.

Lefty
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texas
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Believe me, I was skeptical myself.  I collect old watches and clocks and I've seen every form of trickery under the sun when it comes to cloning something.  That's why I didn't buy from the bay.  I've got fake swiss watch tools that came in the correct packaging and look identical to the real thing.  The illusion falls apart as soon as you start twisting the threaded screws though.  Nobody cuts perfect threads like the swiss.

I'm still shocked at the quality and accuracy of the resonator on the board.  I'm going to pick up another board this weekend and measure the resonator to see if it was just a fluke. 
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OK you were right and I was wrong. Well done.  smiley
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the land of sun+snow
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Quote
I'm still shocked at the quality and accuracy of the resonator on the board.  I'm going to pick up another board this weekend and measure the resonator to see if it was just a fluke.
As lefty indicated, tolerance ratings are no doubt statistical in nature, and individual parts
will lie along a Gaussian distribution, so many will be close to the center, but don't bet
on "always" getting good timing accuracy.

If you get a bad part, and figure out the error at 0.5%, it's really quite significant, if you
want good timing in your sketches. 0.5% is 432 seconds per day, and that comes out to
300 msec per "minute". I don't find that encouraging.
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texas
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Right, I wouldn't expect to get a board that was actually .5% off at room temp.  I'd consider that defective.  I just didn't expect two orders of magnitude better performance than the spec demanded either.  I'm surprised the manufacturer isn't really blowing their horn on that kind of performance.

Thanks GrumpyMike, you guys had me concerned there, for a minute anyway.  smiley-wink
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the land of sun+snow
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The point is, it's all statistics. With crystals, you know the tolerance range is narrow,
so the timing will certainly be good. With the ceramic resonators, it's pot-luck.

Also if you look at the ATmega datasheets, at the tables of RS232 baudrate vs crystal
frequencies, you'll see there already tend to be largish errors with many combinations,
so possible resonator timing errors will just add to that.

Also, since the newer R3 boards have ATmega chips to do USB, and then do RS232 to
the main processor, there may be a compounding of the baudrate error, although
I don't know the specific analysis here. I suppose someone actually double checked
this somewheres along the way.
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Also, since the newer R3 boards have ATmega chips to do USB, and then do RS232 to
the main processor
Don't forget the R2 boards - that's when the 8U2 was introduced into the Arduino chain - certainly for the UNO.
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Also, since the newer R3 boards have ATmega chips to do USB, and then do RS232 to
the main processor
Don't forget the R2 boards - that's when the 8U2 was introduced into the Arduino chain - certainly for the UNO.

Actually the original Uno (I don't think they called it a R1) was introduced with the 8U2 chip and was the first board offered by the arduino folks to use the USB serial converter chip rather then the FTDI USB serial chip that prior USB connected boards used.

Lefty
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ok, so going back to my original question...

If I was measuring time over say an hour, there would be a noticeable difference in accuracy. If however, it was used in an application like music, where the time periods in the low seconds, I can't see how there would be any difference in timing accuracy.

From one second to the next the drift would be so minimal as to be effectively non existent. Everyone agree?
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the land of sun+snow
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If you're doing timing, it could be off by as much as 1 sec over 3 minutes, but for
music, 0.5% variation probably isn't going to be noticeable, I should think. You might
try writing a tone generator set to 1000 and 1005 hz, and see if the difference is
a problem.
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I guess the question I should myself:
What is .5% of a 16th note, and could it actually vary .5% from one 16th note to the next 16th note?
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