The on-board 0.8V, 30A regulator would add about $15-$20 to the design. For 10-15 cards, the money saved would buy a good PSU with voltage trim option.

Either way, the cards work fine if the voltage isn't perfectly regulated. They just run a bit cooler under 12V, and a bit faster/hotter over 12V.

We have a better design

Either they will go to $5/chip and lower, or they will not be sold at all. In the first case, you need a cheap, low-overhead, mining board. In the second case, you don't need a mining board at all.

So far, we have no indication of increased failure rate. The prototypes that we have are rock solid with constant temperature and constant hashing speed. In a couple of weeks, we'll make a few dozen more boards, and we'll see what happens to the failure rate.

These boards don't have additional electronics. On the contrary, a lot of the expensive components have been removed, and the 2-layer board is cheaper too.

And it's not just the cost of the components, but also the availability of some of the more exotic ones.

Another factor is the circuit board design. The fast switching DC/DC regulators typically require at least a 4-layer board for good performance. The One String design uses a cheap 2-layer board.

Correct. You still need a 12V power supply. Each card draws about 2-2.5 Amps, depending on the exact voltage.

That depends on the exact nature of the damage. If the hashing core is damaged (which makes up the biggest part of the chip), the chip may still provide a working connection to the other chips.

It's not much different than low-voltage bitfury designs, such as the H-CARD. In those designs the communication between the chips also forms a chain. Actually, the M-BOARD has 4 H-CARDS with total of 64 chips in each chain.

This design uses 12V to power the chips directly. Other designs, such as the H-CARD have an on-board 12V -> 0.8V power regulator with 30-50Amp capability.

In both cases, you need a 12V supply, but for our new board, you avoid the additional cost of the 0.8V regulator. Also, the 0.8V regulator is typically only about 90% efficient, so it creates 10% more heat for the same hashrate. The powerful switching regulator also produces lots of electrical interference that can degrade reliability of the overall system, and requires additional components (capacitors/inductors) to help reduce the noise.

I don't think Avalon chips have a String feature.

Note that the design is not dependent on the exact type of microcontroller. As long as it has a built-in USB interface, some I/O pins, and a few kB of RAM, it can be used in the design. We picked the LPC because we had already used it on the bi*fury.

The USB interface protocol is the same as for bi*fury, so the latest cgminer/bfgminer version can be used.

What's their total cost for the chip, board, power regulators and cooling system ?

If the bitfury chips become available again, the higher difficulty requires a cheap board. A design like this has minimal BOM cost, so it will be a good solution.

The firmware upload feature is built into the CPU, and because of the very limited memory space it has to make some assumptions about the way the USB mass storage device is used. Native Linux access doesn't work either.  The easiest way to restore the firmware is to use a Windows machine.

You can also write the firmware in Linux, using the mtools:

mcopy -o -i /dev/disk/by-id/usb-NXP_LPC1XXX_IFLASH_ISP-0:0 firmware.bin ::

Once you have the correct firmware, it should work on the Raspi, at least. I don't have a Mac, and I've never tested it on one, so there may be some problem with Mac compatibility.

jedimstr, did you upload the firmware on a Mac ? If so, that may have caused a problem.

I've made an overview of all the different firmware versions, and also included the upgrade manual and the protocol specification that is used between the bi-fury device and the miner software.

http://c-scape.nl/bi-fury/

Added 100 and 110 degree limit versions.

http://c-scape.nl/bi-fury/firmware_100.bin
http://c-scape.nl/bi-fury/firmware_110.bin

If the hash rate is based on the number of shares reported by the device,  big swings are common because sometimes the device is lucky in finding a couple of shares close together, and sometimes it doesn't find anything for a longer period. Because the firmware supports difficulty > 1 shares, the swings can be more pronounced. As long as the long term average is good, I wouldn't worry about it.

Correct. As soon as temperature goes < 90, the chips are enabled, and > 90 they are disabled. So if you keep it around 90C, it will keep switching on/off.

I would think 120-125 deg C is very hot, that's why I set the upper limit at 90.

However, if you'd rather push the envelope a bit, and run the device at 125 deg C, I have uploaded a modified version at http://c-scape.nl/bi-fury/firmware_125.bin

Note that the voltage regulator has a maximum junction temperature of 150 deg C, and it's generating quite a bit of heat itself, so 125 degrees probably causes quite a bit of premature aging in the device. Of course, with the difficulty increasing rapidly, life span may not be very high on your priority list

Edit: I agree with intron. A fan is highly recommended...