Fubarino SD

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sfugarino
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Joined: Tue Apr 15, 2014 10:49 pm

Fubarino SD

Post by sfugarino » Sat Jun 20, 2015 8:03 pm

I know adding a 32.768Khz crystal will allow me to have a RTC, but I am not clear on what capacitors are needed. Does someone have a picture, diagram, or schematic to go by?

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majenko
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Re: Fubarino SD

Post by majenko » Sat Jun 20, 2015 10:31 pm

You need two capacitors - one on each side of the crystal, going to ground. There is space for them on the Fubaruno SD if you are careful with your soldering.

The value depends on your crystal's specifications.
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sfugarino
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Joined: Tue Apr 15, 2014 10:49 pm

Re: Fubarino SD

Post by sfugarino » Sat Jun 20, 2015 11:23 pm

Is that what the four solder pads that are next to the through holes for attaching the crystal are for? And how do you find out the value needed?

djgardn2
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Re: Fubarino SD

Post by djgardn2 » Sun Jun 21, 2015 3:40 am

Hello sfugarino,

Yes that's what the four solder pads are for next to the through holes for the crystal.

For the capacitor in pF, I would recommend you referencing the crystal datasheet that you are planning to buy the crystal from or the crystal you plan to use, for instance looking around I see the usual recommendation is around 12.5pF according to two different websites that sell 32.768 kHz crystals.

The solder pads directly next to the through holes of the crystal is for soldering in the SMD capacitors on, from the looks of it they should be long ways, so in the same placement direction like how the one capacitor next to pin A3 is connected, if you look at the placement direction of the capacitors next to pins 6,7,8 it is not going to be connected in that direction of those capacitors. If this sounds confusing let me know and I will upload a picture later.

For the size of the capacitor (0805, 0603, 0402, etc) I don't think I can help you there (although I can say I don't think they are 0805 size), I'm not familiar with the sizes of SMD (looks like the same size of SMD capacitor as the one next to A3), but hopefully someone else will know.

I believe you will have to have a very steady hand and very small soldering tip in order to manage to solder them on correctly too it seems. Good luck. Anyone feel free to correct me if I am wrong or if you know what the SMD size of the capacitor should be.

Attaching the crystal, you can place it in both the through holes, either side of crystal will work it doesn't matter (there is not a positive or negative lead on the crystal) to my understanding.

Edit: You might find reading the posts in this link useful as well, viewtopic.php?f=6&t=2734 , also I believe that the SMD capacitor size is a 0603 (imperial code size) but be sure to double check yourself first.
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