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Author Topic: FPGA mining for fun and profit  (Read 63997 times)
kjj
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January 05, 2012, 05:26:50 PM
 #221

Currently, the Xilinx Spartan 6 LX-150 is the most common FPGA used for bitcoin mining.  GITHUB has an open source FPGA Miner for this chip, and ztex.de does as well.

Unfortunately, you won't be making a PCB for the LX-150 on a mill.  It's a 484 pin BGA.  It pretty much demands a MINIMUM 4 layer PCB because of the split power needs (3.3V and 1.2V) and ground.

Enigma
Thanks for the heads up, I was just curious as to the process and what not my background is Comp Sci, not so much Comp/Electrical Eng so I don't know much about FPGA's.

I hope that at some point in 2012, I can come back and reread this post and understand what all of these words/letters/numbers mean, haha.

Would a glossary help?

Xilinx is a chip maker.  Spartan 6 is a line of FPGA chips.  LX-150 is a model in that line.

FPGA means Field Programmable Gate Array.  It is a chip with a large number of generic logic gates and programmable interconnections.  This means that it can be configured and reconfigured to do different tasks as needed.  Think of it as a CPU that can be optimized for a particular job.  That's a bit of a simplification, but I think it gives you the idea. 

Github is a public source code repository.  Someone has posted source code that can be loaded into a LX-150 FPGA chip to configure it as a miner.  ztex.de also hosts similar software.

PCB is a printed circuit board, the flat board that electronic components are usually attached to.  Most of them are green.  The board itself is usually a composite insulator material with sheets of copper bonded on the flat sides and then partially removed to leave different connections and circuits.  Commercial boards are etched with acid, but a variety of methods are used for prototyping and home production.  Milling when a rotary tool is used to mechanically cut out portions of the copper layer, usually using a computer controlled machine (a CNC mill, but that's just another acronym to define).  Connections between the sides are done by drilling the board and connecting the copper traces on both sides.  In commercial boards, interconnects are electroplated chemically using processes that aren't generally possible at home, so homemade boards usually use pieces of wire soldered on both sides.

Boards with more than two layers can be made by stacking single sided boards onto a dual layer board so that you end up with alternating layers of copper and insulator.  In commercial boards, the interconnect holes are plated as each layer is added, so it is possible to connect any layer to any other layer.  This is nearly impossible on homemade boards, which is unfortunate because you really need those internal connections (called "blind vias") when working with BGA chips.

BGA means Ball Grid Array.  It means that the chip's pins are all on the bottom, and not along the sides.  The chip is manufactured with a square grid of solder balls on the bottom of the chip, and it is placed onto a PCB with a matching square grid of copper pads and the assembly is heated in an oven until the solder melts and connects the board to the chip.  Because the grid has hundreds of balls (484 in this case) with very tight spacing, there is no room for all of the traces to leave the area on the surface, so they must be connected to internal layers in the board stack and routed out.  Even doing it with 4 layers is rough, 6 is way better.

p2pcoin: a USB/CD/PXE p2pool miner - 1N8ZXx2cuMzqBYSK72X4DAy1UdDbZQNPLf - todo
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rph
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January 06, 2012, 04:25:42 AM
 #222

Unfortunately, you won't be making a PCB for the LX-150 on a mill.  It's a 484 pin BGA.  It pretty much demands a MINIMUM 4 layer PCB because of the split power needs (3.3V and 1.2V) and ground.

There are several successful 2-layer miner designs now, with no problem getting 15W+ into the part.
It takes 6-7 mil trace/space, ~12 mil drills and a good soldermask - so it is still definitely not a "CNC-at-home" PCB.

-rph

Ultra-Low-Cost DIY FPGA Miner: https://bitcointalk.org/index.php?topic=44891
kjj
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January 06, 2012, 07:01:08 AM
 #223

Unfortunately, you won't be making a PCB for the LX-150 on a mill.  It's a 484 pin BGA.  It pretty much demands a MINIMUM 4 layer PCB because of the split power needs (3.3V and 1.2V) and ground.

There are several successful 2-layer miner designs now, with no problem getting 15W+ into the part.
It takes 6-7 mil trace/space, ~12 mil drills and a good soldermask - so it is still definitely not a "CNC-at-home" PCB.

I suppose it helps a lot that bitcoin mining doesn't require much data, so only a few IO pins are needed.  Do you know if these 2 layer boards have any thermal problems?  I know that some BGAs can't dissipate enough heat out the top even with heatsinks.

p2pcoin: a USB/CD/PXE p2pool miner - 1N8ZXx2cuMzqBYSK72X4DAy1UdDbZQNPLf - todo
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