Arduino-Compatible FPGA Shield

Made some updates to the design over the weekend to add LEDs, a nice dipswitch, make the silkscreen cleaner, clean up the pad arrays a bit and a lot more in the way of little cosmetic PCB tweaks.  Overall some very important tweaks but in the grand scheme not functionally hugely different.  Still, will make useability far better.  Some highlights:

- added power and programming LED

- added 4 user LEDs

- added dipswitch with jumpers (making it optional in event you want more IO)

- reworked the pad array and layout to make it easier to fit all of these items

- changed net assignments for JTAG signals to different header pins

- went crazy with silkscreen updates to make board easier to understand

- added some random GND and PWR jumpers to make it easier to get a scope in there and test (also PWR other "things")

Uploaded a new image of the PCB and am currently working on the second round of videos on the board.  

Ok, normally I don't complain about hand soldering stuff because normally it's pretty straight forward but this was a lesson I learned years ago come back to haunt me all over again.  Rule #83: Tent the vias beneath your BGAs!  Especially if you hand solder them.  Point is the surface tension of vias far outweighs that of these tiny BGA pads and thus untented (i.e. exposed from behind the solder mask) these bad boys will suck the BGA part toward the via hole.  Point of fact: not much you can do about this except maybe dap some glue over them.  Not great for production (who hand solders a production board anyway?) but definitely a good trick in a pinch.    Proving once again that boards are only as "bad" as I allow them to be.  Lesson learned, board working...Photos uploaded.  Nerdjitsu! (Thanks mer)

Boards have been built and worked the first time.  Woohoo!  Only thing I've noticed so far is that I neglected to tent the vias (cover them in soldermask) under the super small BGA SRAM.  This has a nasty effect of making it very hard to hand solder these (yes, I hand soldered the BGAs :).  The vias create their own surface tension and can pull the BGA off of it's lands.  Still, managed with patience & a cheap reused stencil I scored from Ian at Dangerous Prototypes at Makerfaire (he was going to leave it behind on his way back to Shenzhen...I recycled it...thanks Ian!), to get the boards to work.  

Anyone interested in testing one, having a whirl with one, what-not, let me know.  I will put up some videos that show me using it and talk u thru the nuts and bolts of the Xilinx development software.  :)

Got boards back from Advanced Circuits today.  Look good.  Really like the finish on them.  They did a good job and boards came back on time (a little early actually) with a bag of microwave popcorn included.  :)  Mmmm...popcorn.  Now I know I'll have ultra greasy hands when trying to solder.  Mmmm...solder.  

I went ahead and added feedback from the fpga DONE pin via the addition of a status LED.  Also added a jumper that enables that feedback to be sent back to the Arduino board.  The jumper gives the option to route the DONE pin to the Arduino via Digital Pin # 7 on the Arduino connector, or for the addition of another FPGA - Arduino Digital IO connection.  If no Arduino board is attached, status will still be displayed via LED and if the LED is undesirable (i.e. inside a case or such) simply DNP.  

As an alternative, there is a second connection to the DONE pin via a testpoint added to the board and the addition of a dual non-inverting buffer, the SN74LVC2G34DCKR.  This should make it (relatively) easy to push this "up" to another board I might have hanging off of this one (e.g. some other non-Arduino MCU board I might have sitting on the desk).

...But it's enough for the board house to balk at, even if they can't mfg to those tolerances.  Oh well, released a slightly modified Gerber to deal with some "roundingness" in the mfg outputs and ensure things are a little cheaper overall (under 5 mil costs more).  Bugger.  Nothing like a finicky board shop to slow you down.  Bet that eats into my "rush" time.   pfft  :|  

Made a cosmetic change the schematic (top level) and also uploaded PDFs to Git.  One small change to PCB was required to get the cost down (increased via hole dia for QFN LDO from 2mm to 2.54mm...makes "low cost" standard mfg avail)

Released a complete collection of manufacturing outputs including Gerber, NC Drill, ODB++, Testpoint files, & Pick and Place.  All of these are for building proper prototypes.  Expect to have boards in 5 days.  2 Days for assembly, a day for test.  If everything works, I'll ship some out to folks who have shown interest and let them tinker with them and provide feedback.

Uploaded the layout files to git today with routing completed and some final schematic tweaks.  Released gerber files also to fab.  Design is looking pretty good and should be pretty close without many major changes since last prototype I'd built from scratch parts at home.  Fingers crossed!

Uploaded the power supply design to git hub today.  The supply is laid out in a way to allow either driving the system from the Arduino's 5V supply or using an external power adapter.  The Arduino's 3V3 supply is tiny (very little current, esp. considering this is the current you'll use to drive 80% of the stuff in any design), thus this design regulates the 5V0 rail from the Arduino or (via jumper selection) from a wall-wart (6V7 - 15V) and produces a proper 3V3 rail with heaps of additional current (3-4x the arduino).  Also includes a 1V2 core voltage for powering the Xilinx FPGA.  

Not particularly glamorous work but this supply also ensures that if you want nothing to do with the Arduino, you can still power the design and have a *very* low cost FPGA development board.  

Apologies to those that asked for this, I was traveling overseas.  Should upload the remaining elements shortly.