Thursday, August 18, 2011
100Mhash/s on the test board at this point, I’ve made a few improvements to the board to get it reach this point. Namely a small heatsink+fan combo and some rubber feet so it doesn’t short on anything on my table. Below are a couple of pictures.
If you (the reader) hasn’t figured out what this is for yet, it’s a bitcoin mining board based on a Spartan-6 LX150 FPGA, at current code, it does 100Mhash/s max, this is estimated to hit 150-200Mhash with improved coding and routing techniques. Me and 2 other guys working together on this project, are aiming to bring this low power, high performance board out as soon as possible, more still to come.
Edit: Alright here's where to buy one, I've only a couple left at the moment.
Not anywhere close to pushing the max limit of the Spartan-6 FPGAs, but here it is, pushing out some real data.
It’s now 6am here, I need sleep.
I need to epoxy on some kinda heatsink to avoid frying my shiny new toy, as well as take some power measurements after I’ve stuck on faster running code. Should be cool.
As above, pictures below, those 0402 decoupling capacitors were kinda hard to get in place. A good magnifying glass really speeds things up.
I assembled the LMZ power modules 1st, they have a huge thermal pad on the back that need serious heat to solder them down.
Here’s the rest of the power supply section tested. Then I metered the output voltages, all within design limitations, before I proceeded (1.2v and 2.5v, measured was 1.18v and 2.48v).
Some noise figures, scope was at 0.2mV/div with an X10 probe, 0% load, I need to retest this again at full load and with a better scope, current scope has a bandwidth limit of 20Mhz, which might not be showing everything.
Then I assembled the rest of the stuff, including the Spartan-6 FPGA, I left some of the capacitors around the sides unassembled so I can visually inspect the BGA soldering quality (didn’t take a picture though).
Next I tackled the underside, which has some 0402 decoupling capacitors. These were insanely hard to do naked eyed.
Here’s a closeup comparison with a 0.5mm ball point pen tip.
This is how I did it by hand (mostly), a good magnifier and strong light helps a lot, you don’t want weird shadows obscuring your view.
A shot of the completed board through the magnifier. It looks good doesn’t it?
Here it’s connected to my cheapie Ebay chinese Xilinx platform cable clone, resting on my messy as hell table.
Wednesday, August 17, 2011
I shall let the pictures do the talking.
PCB cart packed the boards relatively well, they were vacuum sealed with some desiccant inside, the only improvement they could’ve done was to include some kinda moisture indicator.
Preliminary visual inspection and electrical testing has found the board good. I spec’d a 1.6mm PCB, that’s just feels so rigid now I look at it.
The only complaint I have with the current board is due to the HASL finish I employed, the BGA pads are not very flat (or co-planar is the word I think). Nothing some flux and a little solder wick can’t fix.
Will update again later once I get parts onto it.
Sunday, August 14, 2011
Finally completed laying out and ordering part for my upcoming project. I’ll release more details about what it is later, should be exciting.
I had my PCBs made by www.pcbcart.com, my current design uses a 4 layer board, so it’s impossible for me to fab them at home. Short of some communication issues, I think they are fairly good, their lead times are (at your choice) 15 or 18 days (that includes ship time to you) and the prices are pretty reasonable (my board was about 80x60mm and it costs about USD$50 for each). There’s a 1 time tooling cost to generate the artwork (they accept EAGLE files and an operator will put out gerber files for you) and create the stencils+whatnot.
Although I can’t say their command of English was perfect (I had some trouble conveying my requirements across), but eventually I got them sorted. Their email response is fast and if they encounter a problem they’ll message you straight away for a confirmation instead of producing a bad board.
Electrical testing is also provided free as well, which is a good bonus, not cool if your board arrives with an inter-layer short.
As for the parts, well I ordered this time from Digikey, www.digikey.com, instead of my usual RS-components (I use them cause they provide next day delivery, however this time they didn’t have quite a fair bit of the parts I was looking for).
From the ground up my design was based on whatever Digikey had in stock, no point trying to put in a component that’s not easily available. They also do shipping free if your order is over like USD$100 (Might not be the actual figure, gotta check again). Shipping was fast as well, parts actually came before the board.
I’ve yet to receive the boards, so I can’t comment on PCBcart’s quality, but from what I’ve heard/read they are supposed to be not bad. Will update again. Until then….