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Building a Bitcoin miner from Ebay Scrap (Part II)

07 Jun

Well……
The time has finally come to Build our bitcoin miner.

Specification

  • Ebay Scrap FPGA
  • Cost <$100USD
  • Speed >150MH/s
  • UART Interface
  • Standard ATX computer Power supply

A journey of a thousand li begins with a single step
One of the more difficult aspects of using Ebay FPGA scrap is actually selecting suitable donor equipment or suitable donar PCBs.

Key points to identify

  • FPGA Type
  • Powered/Unpowered
  • Guesstimate at approximate integral power supply capability
  • Possible points of connection

FPGA Type
There is absolutely no point on going onto Ebay and getting 400 Spartan 3A’s cheap..
Because the time taken to wire up just 10 FPGA boards has the potential to make you go insane.

Aim for a minimum device specification of:

  • Virtex 5 110T
  • Spartan 6 150

Any FPGA above these devices is a bonus..
Because at-least you can fit a fully unrolled Bit-coin design. Don’t go for anything smaller than the above devices becasue the amount of hashing power available  would make ROI far too long, especially in the current Bit-coin environment .
Remember, the bit-coin difficulty is changing at least +10% every 10 days.

Powered/Unpowered board
Many of the FPGA boards on Ebay are basically ‘scrap’, but there are different types of scrap.

Some of the ‘scrap’ is just an FPGA with a bit of PCB left around it where it was cut from a larger board, You may fantasize that you are going to buy this item, design & build a PCB, build & design a PSU ,re-ball the device, solder it , then write  HDL code to run the device..

Or you can just buy a PCB that contains the  device with  DC/DC brick convertors on already and do a bit of reverse engineering work.

The difference is, that using the latter method, you know at some time in the past the  board worked reliably, plus the power circuitry has been designed by experts and usually implemented on a 16 layer PCB which means the heat is just going to be sucked clean out of the FPGA making your hack all the more stable.
(many Ebay sellers are selling items that actually work anyway…)

Enough Already… tell me the source
Ok
You want this product:
http://www.ebay.com/itm/380632461849?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

Yes I know it says it is sold, but it has since been re-listed.
The price should be about $90USD Each PCB, for that you get TWO FPGA’s and DC/DC power supplies to run the devices.

Don’t worry about the PCI connector, we will be re-engineering the board with ONLY 5 connections!!.

  • 12V
  • 3V3
  • 0v (GND)
  • RS232 RX
  • RS232 TX

The FPGA source for bit-coin on Xilinx devices is already available online via github, but I will be linking to a pre-compiled BIT file.

List of required parts

  • Fora E03251-2 board
  • JTAG cable
  • RS232 Board
  • ATX power supply
  • 2-3 Maglev Sunon 12v fans (ME50151V1-0000-A99)
  • 2 Heatsinks(36mm*36mm*25mm)

How do I know it will work?
Because I already have one working reliably for a couple of days.

board

proof

Breakdown of forthcoming  tasks

  • Outline connections for UART (not a big job… two/three soldered wires)
  • Look at getting the supply to just 12v (I’ve had difficult times with 3V3 supplies)
  • Possible increase in speed, This depends on the DC/DC convertors.

Unfortunately, FOR-A did a piss poor job of designing the power supplies as well as the FPGA Layout.
I have ‘heard’ some of the Ceramic caps breaking over on the memory & infrastructure areas of the PCB.
Hopefully we can strip these out, since they should not be needed for the FPGAs and as long as we tri-state the related FPGA pins the current consumption should be lower.

Just a Tip (FOR-A) guys… when you design with an FPGA bring ALL the pads through the board with VIAS, because the way you have done it leads to a number of serious issues related to product reliability….

 

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