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Topic: ATMEL Mega1284P evaluation board avalible (Read 180076 times) previous topic - next topic

pito

..cr1220 would be more elegant, as I wrote few times.. :smiley-yell:

http://shop.ebay.com/i.html?_from=R40&_trksid=m570.l2736&_nkw=cr1220++holder

CrossRoads

Okay westfw and pito, after a nights sleep, I am willing to add another mounting hole for a smaller coin cell battery holder, wired in parallel with the existing, if you can help me with a symbol for it.
You can see space is a little tight in that area. Options are to use the existing Bat+ hole and add a new Bat- hole, or use the existing Bat- hole and add a new Bat+ hole.

Ah! I see it is surface mount - that will be easier to add, there are not too many bottom traces in that area.



Rats! I went thru a lot of effort to make sure no thru parts would interfere with the battery holder - then stuck a thru hole +5V regulator right in the middle of it!  Back to the drawing board - or, forming the TO-220 leads. Really wanted thru hole for mechanical strength tho to support addition of a heat sink.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

CrossRoads

Is there a way to make eagle only show the +5V traces? I am concerned that with my multiple revisions to the regulator area that I have +5 routed in multiple paths to some of the same parts.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

mmcp42

click on the eye symbol, then select a trace - shows u all of it!
there are only 10 types of people
them that understands binary
and them that doesn't

pito

@skyjumper:
- re decoupling capacitor at sd-card sockets - this is not about the current the voltage regulator can source, but about a transient caused by a pulse of high current when selecting the sdcard and the _maybe_high_ impedance of the pcb trace coming from regulator to the sdcards..
- card detect - yes, we may detect it by software outside the sdfat (or the detection will be implemented in sdfat as well), however, we need the signal from both cards ..
P.

CrossRoads

@mmcp42: Cool, thanks. That helped, found a couple of hand edits where thin traces got put in, and the star distribution of power had definitely become a little funny.

@pito:
The regulator & its 100uF input cap and 100nf output cap are located next to the SD card on skyjumpers board, I think he is in good shape there.

Are you able to find a symbol for a CR1220 battery holder? The only one I came across was the adafruit metal holder which didn't appear to be insulated on the board side, I need that to insure traces do not get shorted out by the battery wearing thru the solder mask.

Robert
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

pito

#261
Jun 26, 2011, 09:45 am Last Edit: Jun 26, 2011, 10:23 am by pito Reason: 1
Robert,
- for example: here are 2 eagle files, you can open them and copy the battery holder part..

http://garden.seeedstudio.com/index.php?title=Wiseduino

http://www.wiseduino.com/?cat=3

- the cr1220 battery holder on the board seems to be this type:

http://www.ebay.com.au/itm/10pcs-CR1220-1220-Computer-Battery-Socket-Holder-Case-/300553623491?pt=AU_B_I_Electrical_Test_Equipment&hash=item45fa6457c3


CrossRoads

So I've traded some e-mails with the company that made skyjumpers stencils for his board, which had some bridging issues after reflow on the FTDI chip.
The guy I'm talking to says 28 SSOP are the devil's work! 8)
He suggested he would adjust the stencil opening to be 2mil narrower in all directions - but suggested instead going to the 32 pin QFN package.
Does anyone have a line on  part that uses 32 QFN with thermal pad on the bottom that I could edit into an FT232RL?

I know I could do it from scratch, but my eagle skills are slow in that area, took me several nights to come up with this FCI socket, doing the math calculations, intrepreting the mechanical data sheet.
(I can't even locate the library I created!  Eagle has it tucked away somewhere - I can open it & see my part, I just can't see it on my harddrive anywhere!)
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

westfw

It looks like the "ftdichip" library that comes with EAGLE includes the QFN version...

skyjumper

I have been thinking about this and I think I would avoid QFN (quad flat no-lead). Without an x ray machine, there is no way to inspect the component after reflow, so there could be bridges you would never see. If there are bridges, the only way to fix them is to remove the entire chip. Since it has four sides, removing it, even with a hot air rework station, is going to be a challenge. And then, how do you get it back on without disturbing the neighboring components? You can not hand solder it, because there are, well, no leads. And, assembly houses charge more if your board has no lead components and/or fine pitch components (but FTDI chip is not fine pitch).

I have been told by many people that swelling the apertures works well to solve the bridge problem. The FTDI chip does have tight leads, but they are not technically small enough to be referred to as "fine pitch." Without swelling the apertures, I got bridges, but I was able to wick them up and all was fine. I doubt I could do that with QFN.

Just my 2 cents. On the other side, heck, I'm willing to give it a try! Maybe I'll be pleasantly surprised!



CrossRoads

Dang! Look the bodies of the 2 chips.
I'm liking the 28SSOP more after seeing them together.
I think I'm with you, swelled aperture.

I just spent a couple of hours creating a footprint too, as I didn't have an option for QFN - but I see why, somehow I grabbed the FT232 from the "smartprj" instead of the "ftdichip" - probably because I started out by stripping down a duemilanove and building back up.
The two libraries use diferent looking symbols too for the 28ssop part/
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

skyjumper

That's amazing. And that stencil guy thought this would be an improvement? Well, to be fair, maybe there are QFN packages with bigger pins and spaceing.


CrossRoads

First lot of 10 PCBs ordered, sans the small battery.
Stencil & parts ordering next ...
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.



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