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Author Topic: GekkoScience BM1384 Project Development Discussion  (Read 145329 times)
MrTeal
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April 10, 2015, 02:47:52 AM
 #401

Also, tomorrow is Friday which means Cheeseburger Day. So I won't actually be working all day. Gotta make time for sammiches.
How many sammiches are involved in a typical Cheeseburger Day?
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sidehack
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April 10, 2015, 03:12:29 AM
 #402

I typically eat 3 cheeseburgers, 5 hashbrowns and between 6 and 8 glasses of tea.

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April 10, 2015, 08:26:11 AM
 #403

I typically eat 3 cheeseburgers, 5 hashbrowns and between 6 and 8 glasses of tea.

Sweet tea Huh   & I'm not making a pass at you  Cheesy

"If you run into an asshole in the morning, you ran into an asshole. If you run into assholes all day long, you are the asshole."  -Raylan Givens
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"An ASIC being late is perfectly normal, predictable, and legal..."Hashfast & BFL slogan Smiley
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April 10, 2015, 01:01:16 PM
 #404

Yes, sweet tea.

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April 10, 2015, 02:44:12 PM
 #405

With ice. It is already getting warm down South.
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April 10, 2015, 06:25:33 PM
 #406

Got LED stuff figured out and the board design modified to reflect the changes in LED drive and regulator. Sent an updated heatsink spec to the heatsink people. I'll have to do some recalculating on the regulator to shift the adjustable range from 0.65 to 0.80, instead of 0.55 to 0.75 since it appears the chip won't work on most of that low range anyway. As this affects the feedback values, it also affects the frequency compensation values so will require some more testing.

By the way, the LED color scheme is pretty sexy.

I'm also going to rig up a USB extension, possibly externally powered, that'll allow me to directly measure input power so we can get some sample efficiency curves off the prototype boards. Since the various modules (right now two PCBs, one of Novak's Prisma adapters and some breadboarding) are basically identical to the Compac as it stands, the power requirements should be pretty close to accurate.

Also, we're currently at a board size of 1x2.16 inches which puts it at almost the same size as an Avalon Nano (slightly narrower, slightly longer). The heatsink we're looking at to be 25mm square and top-mounted, which means the fins are facing upward on basically all the PC USB ports I have looked at. The AntMiner U2 heatsink is 25x40mm. If we were doing rear-side heatsinking I could use a full 25x50mm heatsink but I'm not sure how much cooling comes from the bottom on this chip, given Bitmain has zero designs using bottom heatsinking. I don't know if that's because the chip is designed to top-cool, or because of potential ground plane issues with string designs, or both.
If people are concerned about requiring a larger heatsink, I can get a larger heatsink and not change the Compac PCB size, where the extra length of heatsink will be sticking out past the end of the board.

If we end up doing the Amita (the two-chip string) as well, the board will probably have to be wider to accomodate some extra buffer capacitors to help out with node-level core voltage stability. Since I'm planning on just using two Compac heatsinks on the Amita instead of spec'ing a second heatsink, any changes to the heatsink dimension will cause additional changes to the Amita dimension, as the board length will have to accomodate a full heatsink plus as much of a second as doesn't overhang the board.

The total thickness, given that the heatsink will be on the same side as the rest of the parts, should be no more than 14mm. This is PCB thickness plus ASIC thickness plus a small shim plus 10mm heatsink. I figure y'all guys with compact hubs should appreciate this dimension.

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April 10, 2015, 06:44:55 PM
 #407

Also, we're currently at a board size of 1x2.16 inches which puts it at almost the same size as an Avalon Nano (slightly narrower, slightly longer).
Sounds like it'd be almost exactly the same size as the rectangular part of a hex•fury, which was a rather compact design for 6 chips Smiley

Sounds like it should fit quite nicely into the original BE cases and readily fit inside Antminer U1/U2 magnetic latch type cases.

Looks like the one under test (at the burger address) has been fairly stable as well - very nice! Smiley

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April 10, 2015, 07:04:45 PM
 #408

I'm not sure how much it's a problem of hot restarting or just that the prototype's pretty jankety right now with wires on headers flopping everywhere, but sometimes when it cuts out it decides not to come back online for a few minutes. I've noticed it's not as stable at 125MHz as it was at 100MHz, which could be heat-related or voltage-related. It'll take some more testing to be sure of which.
I pulled the test board this morning to play a bit with the LED drive, so that cost a few minutes of hashing, but it's been running alright basically continuously for the last two days and some. The regulator has no heatsinking, and the chip has about a 2cmx3cm thing taped onto it not very fancily.

I'm pretty sure we won't be selling these in cases. It adds to the cost and how many folks are going to just chuck 'em anyway?

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April 10, 2015, 08:39:33 PM
 #409

I'm pretty sure we won't be selling these in cases. It adds to the cost and how many folks are going to just chuck 'em anyway?
Nah, but I might should I end up buying a bunch for reselling/gifting - wouldn't add that much cost on my end Smiley

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April 10, 2015, 11:35:02 PM
 #410

Got LED stuff figured out and the board design modified to reflect the changes in LED drive and regulator. Sent an updated heatsink spec to the heatsink people. I'll have to do some recalculating on the regulator to shift the adjustable range from 0.65 to 0.80, instead of 0.55 to 0.75 since it appears the chip won't work on most of that low range anyway. As this affects the feedback values, it also affects the frequency compensation values so will require some more testing.

By the way, the LED color scheme is pretty sexy.

I'm also going to rig up a USB extension, possibly externally powered, that'll allow me to directly measure input power so we can get some sample efficiency curves off the prototype boards. Since the various modules (right now two PCBs, one of Novak's Prisma adapters and some breadboarding) are basically identical to the Compac as it stands, the power requirements should be pretty close to accurate.

Also, we're currently at a board size of 1x2.16 inches which puts it at almost the same size as an Avalon Nano (slightly narrower, slightly longer). The heatsink we're looking at to be 25mm square and top-mounted, which means the fins are facing upward on basically all the PC USB ports I have looked at. The AntMiner U2 heatsink is 25x40mm. If we were doing rear-side heatsinking I could use a full 25x50mm heatsink but I'm not sure how much cooling comes from the bottom on this chip, given Bitmain has zero designs using bottom heatsinking. I don't know if that's because the chip is designed to top-cool, or because of potential ground plane issues with string designs, or both.
If people are concerned about requiring a larger heatsink, I can get a larger heatsink and not change the Compac PCB size, where the extra length of heatsink will be sticking out past the end of the board.

If we end up doing the Amita (the two-chip string) as well, the board will probably have to be wider to accomodate some extra buffer capacitors to help out with node-level core voltage stability. Since I'm planning on just using two Compac heatsinks on the Amita instead of spec'ing a second heatsink, any changes to the heatsink dimension will cause additional changes to the Amita dimension, as the board length will have to accomodate a full heatsink plus as much of a second as doesn't overhang the board.

The total thickness, given that the heatsink will be on the same side as the rest of the parts, should be no more than 14mm. This is PCB thickness plus ASIC thickness plus a small shim plus 10mm heatsink. I figure y'all guys with compact hubs should appreciate this dimension.

so the watts translation for the volts =?
the hash translation for the volts =?

ie:  at the 0.65  volts are we at 2.5 watts and 6gh?

at the 0.80 volts are we at 5 watts and 10 gh?

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April 10, 2015, 11:52:33 PM
 #411

You already quoted the answer to your question:

"I'm also going to rig up a USB extension, possibly externally powered, that'll allow me to directly measure input power so we can get some sample efficiency curves off the prototype boards. Since the various modules (right now two PCBs, one of Novak's Prisma adapters and some breadboarding) are basically identical to the Compac as it stands, the power requirements should be pretty close to accurate."

Which is to say, I have not tested this yet but it's on my list for the near term - probably this weekend. Also, the watts and hashes per volt are a whole field of curves dependent on the operating frequency, so there's no simple answer. Once I have the power metering set up I'll probably have to spend a whole day testing different operating voltages at set frequencies (hashrates) to see what's stable and get a series of efficiency curves.

As an initial estimate, I believe the 6GH point I'm at right now should be pulling around 2.1W but I haven't measured that, it's based mostly off theoreticals. Yes, that makes this stick miner more power-efficient than the S5.

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April 11, 2015, 12:28:41 AM
 #412

You already quoted the answer to your question:

"I'm also going to rig up a USB extension, possibly externally powered, that'll allow me to directly measure input power so we can get some sample efficiency curves off the prototype boards. Since the various modules (right now two PCBs, one of Novak's Prisma adapters and some breadboarding) are basically identical to the Compac as it stands, the power requirements should be pretty close to accurate."

Which is to say, I have not tested this yet but it's on my list for the near term - probably this weekend. Also, the watts and hashes per volt are a whole field of curves dependent on the operating frequency, so there's no simple answer. Once I have the power metering set up I'll probably have to spend a whole day testing different operating voltages at set frequencies (hashrates) to see what's stable and get a series of efficiency curves.

As an initial estimate, I believe the 6GH point I'm at right now should be pulling around 2.1W but I haven't measured that, it's based mostly off theoreticals. Yes, that makes this stick miner more power-efficient than the S5.
 

that means it will sell.  I want some please.

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April 11, 2015, 12:48:19 AM
 #413

I just finished rebuilding the test regulator for the third time (which makes this iteration number 4) and am about to load-test it. The present design adjusts between 650mV and 800mV and hopefully remains stable at currents above 4A output.

If it behaves well enough, tomorrow I'll look at running it on the hashboard and see about getting some initial W/GH estimates.

Phil, you're on the short list for receiving prototypes to field-test. If the current iteration of the regulator design is good enough, we'll probably be sending off for prototype PCBs early next week and start populating for testing the week after. Which is going to be a pain to do by hand. The bottom half of the board is freakin' dense. In one square inch there's the CP2102 USB/UART chip, a UART level shifter, two LDOs, the oscillator, two LEDs, a couple FETs, and the entire regulator circuit with its approximately two dozen support components. But that's what happens when you build an 8A VRM onto a stick miner for a chip that needs 3 different voltages and takes 1.8V IO and requires a topside heatsink. But we designed the whole thing with nothing smaller than 0603 parts so it's actually possible to do by hand until we can get a decent robot. The worst part will actually be the ASIC itself, since it's a no-leads chip with a belly pad. If there's a hair too much solder on the belly pad (or the VDD corner pads) the thing floats too high and the data pins don't make contact with their pads. So it requires very careful pasting and very precise placement. Which if we don't have good machinery is going to make assembly suck balls, especially on TypeZero boards with a whole bucket of chips.

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April 11, 2015, 02:36:52 AM
 #414

I just finished rebuilding the test regulator for the third time (which makes this iteration number 4) and am about to load-test it. The present design adjusts between 650mV and 800mV and hopefully remains stable at currents above 4A output.

If it behaves well enough, tomorrow I'll look at running it on the hashboard and see about getting some initial W/GH estimates.

Phil, you're on the short list for receiving prototypes to field-test. If the current iteration of the regulator design is good enough, we'll probably be sending off for prototype PCBs early next week and start populating for testing the week after. Which is going to be a pain to do by hand. The bottom half of the board is freakin' dense. In one square inch there's the CP2102 USB/UART chip, a UART level shifter, two LDOs, the oscillator, two LEDs, a couple FETs, and the entire regulator circuit with its approximately two dozen support components. But that's what happens when you build an 8A VRM onto a stick miner for a chip that needs 3 different voltages and takes 1.8V IO and requires a topside heatsink. But we designed the whole thing with nothing smaller than 0603 parts so it's actually possible to do by hand until we can get a decent robot. The worst part will actually be the ASIC itself, since it's a no-leads chip with a belly pad. If there's a hair too much solder on the belly pad (or the VDD corner pads) the thing floats too high and the data pins don't make contact with their pads. So it requires very careful pasting and very precise placement. Which if we don't have good machinery is going to make assembly suck balls, especially on TypeZero boards with a whole bucket of chips.

I'd be happy to help test a miner as well if you need additional field testers.
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April 11, 2015, 02:39:56 AM
 #415

Let me know if you want me to test one usb proto board!  Wink

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April 11, 2015, 04:17:47 AM
 #416

So, the new regulator iteration has been tested to its limit. I did get over 5A out of it at several tested voltage setpoints, but that's still not really great. I'm hoping when it's mounted on a proper board with better heat dissipation it doesn't wig out quite as much.

Here's a chart of actual regulator performance. The current output is an estimate based off using low fixed resistance loads and not directly measuring current, so the actual current (and therefore actual efficiency) could be skewed, even though I was using 1% tolerance resistors. Wiring and solder joins can have a large effect on overall resistance when the overall resistance is pretty low to begin with.



And now, the fun parts. Based on the current outputs and measured regulator efficiency at various voltages, and extrapolating from Bitmain's efficiency and performance charts for the BM1384, here's some expected performance data on the Compac.





Looks to me like 7GH off a standard 2.5W USB port is attainable at 675mV. The regulator as designed should give us 650mV as a lowerbound, but I had to approximate some of the component values for this test which has shifted the feedback slightly high. It's actually higher than I'd estimated (675mV versus an expected 660mV) but that's not terribly surprising. At 650mV, if the chip'll even start (should, but no guarantees) 8GH should be possible from a stock USB power. This is, unfortunately, not taking into account the added power consumption of the CP2102, IO and PLL LDOs, and LEDs. This all shouldn't add up to a substantial amount of power, but when the ceiling is 2.5W everything needs to be taken into consideration. But that's a job for another day.

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April 11, 2015, 04:49:14 AM
 #417




P0RN! YESH!

when you're done soldering, burning, drilling and popping smoke out of it, i might have to consider buying that toy off you...

I typically eat 3 cheeseburgers, 5 hashbrowns and between 6 and 8 glasses of tea.

it been many years since i've had a cheeseburger, i blame the local maccas and the 14yo's that "like, have better things to do and like, stuff" they have hired. (try ordering a cheeseburger, without any cheese, you'll get my picture)

as for the technical stuff, them there some purty lines you gots there on them pictures!
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April 11, 2015, 05:01:58 AM
 #418

Surprisingly enough, there has been zero smoke so far. I did throw off a part or two while trying to debug some issues with one board, but I think they're probably actually still functional. I was really surprised the regulator didn't blow up, but that PCB was literally the best toner-transfer etch Novak has ever done. Super precise and not a single cut trace. I might throw together an LED board so I can have my breadboard back, and get some updated pictures. But the more pressing priority will be getting actual hashrate efficiency curves off of it, instead of extrapolations and estimates.

That particular toy in the picture will never be sold. It's a landmark thing for us. Maybe you can buy one of the finished product Compacs, but not the test hardware.

Also, I tend to fetch cheeseburgers from the Waffle House. There's something nice about being able to watch food being cooked before you eat it - you know exactly how fresh it is, that that patty hasn't been sitting under a heat lamp for the last five hours. Also, for the cost of a large fries at a fast food joint I can get about a pound and a half of hash browns, which are better anyway.

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April 11, 2015, 05:34:46 AM
 #419

Great job man!  Just might plug my block erupters back in to pay omage to your hard work.  I'd like to run a few when your done just for the pretty leds. 
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April 11, 2015, 05:50:56 AM
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that PCB was literally the best toner-transfer etch Novak has ever done. Super precise and not a single cut trace.

I don't mean to brag, but yes, yes it was.  The tolerances on that regulator board you drew up were tighter than the smallest allowable by our usual PCB fab.  Not to say that I held all the tolerances but every pad and trace were at least usable.  Not bad when some of the gaps between traces were literally fractional pixels.


But the more pressing priority will be getting actual hashrate efficiency curves off of it, instead of extrapolations and estimates.

I'm pretty curious to see that myself.  Should be all kinds of fun to get real numbers out of it.

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