I've looked at component availability, digikey should have all the parts I've put down, capacitor ESRs are pretty critical.

I'm also doubting that this board will be useful as an experimental platform, alot of the GTP is not present, there's no memory at this point in time, even the PSU for Vccio is shared with Vccaux, which is non optimal if there's alot of IO activity. We're gonna also have to add some connectors for the IOs (more routing, layers probably)

We could work out all of these limitations, but in the end I think our board will just end up being more expensive. I wouldn't go for it.

Added updated layout + schematic files for the PSU and BOM to the dropbox, I think that is alot easier to use then Github for this.

Here's the PSU I've layed out.

http://www.dropbox.com/gallery/19035447/1/FPGA?h=b7ac9a

http://dl.dropbox.com/u/19035447/FPGA%20PSU.sch

I've split up the Vccint reg for easier layout, thermal management and headroom.
Vccaux and Vccio are both tied together and set at 2.5v, I think if we want to use the board not just for Bitcoin mining, we might have to split the supplies, or at least filter the Vccaux with ferrite beads.

I've left alot of headroom for this design, the modules are also easy to use, very few external parts, and are hand solderable if we decide to prototype or change anything.

Would be nice to have an extra pair of eyes to check the work before we send it out for production, sure could use some layout optimization as well. Are you good with coding? We'd preferably want a little bit to code to run some tests on the fresh hardware that rolls out, I'd suppose you'd need to wait for more routing details to come up before you can do anything though.

Do you think adding 1-2 debug LEDs will be useful? Or maybe testpoints.

We haven't sorted out how best to share updates, I have done up the power supply section (at least the schematic).

Doing the power supply, do I just draw up the schematic so we can route later into the main board ? I'm having some fun creating the part library though LOL.

Vias directly under pads, I wouldn't recommend it, that hole, even if solder doesn't suck down into it, can create voids due to air migrating up.

Best to connect up the rest of the supply pins together in a criss cross net and via that centre point.

The solder pad itself can be .4mm, but the solder mask clearance around the pad should be .5mm. We should be able to easily fit the design into 4 layers, 2 for power and ground planes.

Again I can assemble the prototype boards for close to nothing. We can decide on this later when the design is finalised.


What kinda voltages are we planning to use for the various rails? Perhaps I can start on the power supply design.

The prices for populating are for 1 board? That price is inclusive or exclusive of the parts cost? It may be necessary to goto a 4 layer board, and then put the regs and decoupling caps on the backside. We're probably gonna have problems routing the LTM4627 output traces for 10+A without multiple vias that conduct to a power + ground plane.

The community has already decided to include the option of using laptop power supplies (that run anywhere from 12 to 20V) to power the design, electrically it might not seem like the best of all ideas, the higher input voltages usually mean a lower efficiency. With the reg I have in mind, even at 16V in we'd be getting around 70ish % efficiency, not too shabby. Transient and ripple also look good (at least in the datasheet, layout and parts will have an impact).

It's not a bad thing to have, a person aiming for max efficiency has the option to go out and get a suitable adapter that'll get you better efficiency figures.

Maybe we can simplify even further for prototyping by using National's simple switchers, eg the LMZ22010

http://www.national.com/pf/LM/LMZ22010.html#Overview

This reg uses very few external parts, houses an internal shielded inductor, each puts out 10A and we can place each part near the FPGA for easier routing/decoupling. The only con I guess is the slightly higher cost per part.

*edit I've looked at digikey pricing, and it doesn't seem all that far apart if we use 2x 8A parts (each feeding the FPGA), I think we need to seriously come up with some reliable power consumption figures, anyone with a demo board/dev kit want to confirm the figures for us? That'd be a great help.

LAYER <layer number or layer name> will change layers. I prefer to type more then click around.

Yup, that's right, not currently equipped out at the moment to do PCBs professionally (I can only do double sided). Certaintly something we do not want to skimp on, a good quality properly routed board will make or break the prototyping stage, the layout can be optimised later to be more cost effective. I'd like to, at least for the start, not use any parts smaller then 0603 if there's no real need to, and reduce the use of QFNs, they're harder to inspect visually, and the foot print is not much bigger for QFP parts, neither is it really cheaper.

I'll be happy to produce the 1st ten boards for $0, just to get this project up and running and to debug/iron out any issues we might have. Just throw the blank PCB and parts in my direction and I'll get right to work.

At this point of time, it's more of a hobby/fun thing to do then monetary, perhaps later on I'll add a donation link or something somewhere. I hope to get 1 FPGA board myself to keep. As a start I think we need to figure out if the demand is there, so I hope this will help out. I will continue to support this for as long as I possibly can, and if at any time I feel I might not meet datelines and/or the demand is starting to pickup I'll update.

I'd hate to see this turn out into a Funcube Dongle, whereby the hardware is known to exist, but can't be bought because the demand exceeds supply. So yes, I'd say I'll stop at 50 boards, unless the demand is really trickling in and we want to keep production costs low.

I'd like to add that if we were to populate the 1st few boards ourselves, before letting a board house do it, it'd be possible to test out the Vregs beforehand to make sure they work properly before putting down the $$$ FPGAs.

No problems with $160 ICs, so long as the board and part is dehumidified (I put them through an oven if I'm unsure, packing them properly with dessicant helps alot here), I can put them down properly. I have plenty of time till the end of the year to work on this at the moment, I agree that once production rates need to ramp up, it's be alot better to get it done professionally through a board house, but for the 1st few protos, I can volunteer to assemble them up. Even if the FPGAs were say pulled from a working board, I can also reball and solder them down to the new board (Not sure if we'll take this route).


I can easily do reflow on the back side of the board as well if the need arises, I personally hate QFN packages myself, some of them that have pads that don't wrap around to the top side are a pain to work on, you can't inspect them after you've soldered them down, and you're not always quite sure how much paste to apply on the centre pad.


Haha, not quite, I'm based in Singapore at the moment, so yeah my posting times might be alittle weird.

Hi guys, I have access to BGA rework/repair equipment, if a prototype batch needs to be made, say about 50 boards max, I can assemble and test them out.

http://fillwithcoolblogname.blogspot.com/

That's my blog. I usually do Xbox 360 reballs. I'm new to the bitcoin scene, but not new to electronics.

At this point I think we just need to iron out the PSU requirements, and then design a board to fit all this in. Once that's done we can start drawing up a schematic and then try routing a board that'll fit (and is not too expensive), whilst the bus decision is being finalised. As for populating the backside, I don't think that's a major problem, if cost is prohibitive I figure we can manually solder them on by hand (if the components are say decoupling capacitors and sockets.). just my 2cents.

Hi,
I'd love to be whitelisted. Although I'm new to bitcoin, I'm not new to electronics/PCB design. I'm actually looking to post in the FPGA section (usually I just lurk around in forums until I have something to add). I'm sure I'd add value to the ongoing discussion on that side.

http://fillwithcoolblogname.blogspot.com/

That's my blog, I have access to BGA rework/repair equipment at work and I'd be glad to assist in anyway.

I seldom post on forums if at all, usually I spend most of the time just reading. This system doesn't work too well for me, to actually rack up 5 posts might take me fair bit of time.