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particle-iot / core

Hardware design files for the Spark Core, a tiny Wi-Fi development kit.
https://www.spark.io/
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Revert back to 5mm x 3.2mm crystal footprint #32

Closed zsup closed 10 years ago

zsup commented 10 years ago

Turns out we can't find an 8Mhz crystal at 3.2mm x 2.5mm, so we're going to have to figure out how to squeeze the 5mm x 3.2mm crystal back on there. I think we can shift down the capacitors on the bottom of the board; will be tricky to figure out how to make room, so we should dig into this ASAP to see if it's feasible or if we need to make more significant modifications

mohitbhoite commented 10 years ago

On a side note, this is another option in same dimension but with two pins: http://www.ndk.com/images/products/catalog/c_NX3225GD-STD-CRA-3_e.pdf DigiKey has 7K in stock. I have contacted a sales rep to see if we can get them for immediate purchase at better pricing.

brandoaire commented 10 years ago

Good find. That must have literally been added to the site in the last 24 hours because 8MHz + 3.2x2.5mm package size yielded no results when I checked the site yesterday morning, and now the NDK part is the only result. Is the lower load capacitance (8pF instead of 18pF as originally spec'ed) an issue for this part?

mohitbhoite commented 10 years ago

Their frequency stability looks poorer (+-150ppm) as compared to the 3.2x5.0 version (+-50ppm). I'm not sure how dramatically will this affect the performance of the Core. (But they also claim to be automotive grade)

andyw-lala commented 10 years ago

Since we have a 32KHz rtc xtal, I think the 8MHz freq stability is not important. 150ppm is fine.

On Tue, Jul 16, 2013 at 7:43 AM, Mohit Bhoite notifications@github.comwrote:

Their frequency stability looks poorer (+-150ppm) as compared to the 3.2x5.0 version (+-50ppm). I'm not sure how dramatically will this affect the performance of the Core.

— Reply to this email directly or view it on GitHubhttps://github.com/sprk/core/issues/32#issuecomment-21039174 .

Andy

mohitbhoite commented 10 years ago

@satishgn Zach and I came up with a tentative layout for the 5x3.2 crystal on the core. I'm attaching a screenshot for your reference. (I didn't run a drc on it, but it seems doable)

core-bottom-new-crystal

zsup commented 10 years ago

Alternately to reduce the distance between the capacitors and the pads of the crystal, one of the capacitors for the 8Mhz crystal could be moved above the crystal, and the crystal could be shifted downwards.

satishgn commented 10 years ago

I didn't find the layout files corresponding to the above image in the dev folder. I was especially looking for the crystal footprint of 5x3.2 as the datasheet is not readable. just didn't want to reproduce the above done work.

satishgn commented 10 years ago

Ok. I found one such crystal footprint(5x3) in SparkFun Library.

mohitbhoite commented 10 years ago

Sorry about the confusion there @satishgn I just quickly mocked up the layout for your reference to see if it could be done.

satishgn commented 10 years ago

no problem. I have pushed some changes to the Dev branch.

On Wed, Jul 17, 2013 at 10:18 PM, Mohit Bhoite notifications@github.comwrote:

Sorry about the confusion there @satishgn https://github.com/satishgn I just quickly mocked up the layout for your reference to see if it could be done.

— Reply to this email directly or view it on GitHubhttps://github.com/sprk/core/issues/32#issuecomment-21126821 .

satishgn commented 10 years ago

Implemented.

zsup commented 10 years ago

looks good - good work squeezing it into the small space.