Topic: GekkoScience BM1384 Project Development Discussion - page 90. (Read 146665 times)

I created my account on btctalk only to support this project, greet with the developer/s and wait for the product  

Big board (1kw) whould be killer !!


great job and knowledge.. definitely the most interesting thread to follow!

thanks

Edit: why not a multi usb board in the box... with common cooling... but any usb miner can be unplugged on need.. and only electrical imput and usb imput available from outside...(Gridseed G-blade style)

I am looking more and more forward to getting some of these. I think your approach is great.

heh ....you should daisy chain your boards into a small box for more GH heh

I know I know just get a usb hub...and a gaggle of them

just saying

A fully tweakable usb miner at last.  Hope the heatsink works out.  Can't wait to grab a few from you when done.  Sandwich fund growing.

So, updates. I built a USB port with current metering built in. It's got a pin header for taking in external power, or jumper a pair to use current from the USB upstream. I checked the calibration on the current measurement with about nine data points and it looks to read 3.5% high, so that'll be taken into account on all calculations.

After talking with Novak and looking over the hashrate extrapolation charts from last night, I'm going to do some more shifting on the regulator. We do still like that low end of the range, around 625mV, and there's no practical reason for the Compac to run higher than 750mV unless you want to pull more than 2A from your USB port for marginal hashrate gains. Which seems dangerous and not recommended.

With the wiring I have now between the regulator and breakout board, I'm seeing a fairly significant voltage drop (10mV or so) at the Vcore pins on the breakout board. So my starting voltage right now is definitely not the same as my running voltage. I've got it running 125MHz/6.875GH right now, starting voltage 635mV running voltage 625mV at a current draw of about 483mA off a 4.85V USB line. This is about 2.34W, so about 0.34W/GH which isn't too bad. I need to recalculate the regulator AGAIN (iteration 5) to shift the adjustment range to 600-750mV.

I think some of the instability I'm seeing from higher current outputs is more related to the compensation loop than temperature problems. I squeezed my feedback resistor down a ways to get 600mV, which throws off the frequency response of the compensation, and now when the chip tries to start at 150MHz/640mV it wigs out like it was doing during the upper ends of my load tests. So that's something I'll have to play with. I'm also thinking of, for the test board, pulling the feedback sense directly off the breakout board instead of the regulator board, which will take the wiring into account for regulation and should cancel out that difference between running voltage and starting voltage. Improve load regulation, that is to say.

So, maybe tomorrow afternoon I'll rework the regulator back to stable at the new adjustment range and get some good efficiency curves. Novak's gonna be looking into integrating the arbitrary frequency code I wrote some months back for S1 workups into a cgminer driver so we aren't limited to the stock settings like 100/125/150. The code takes in an arbitrary frequency and generates the hex value for the nearest compatible frequency that the chips' PLL multiplier can operate at. So once that's in, we'll be able to get efficiency curves with a much higher granularity - every 3-5MHz instead of every 25. And hopefully the regulator will be plenty stable up to 5W input, which at the bottom end 625mV would be about 6.5A output. I haven't tested it successfully up that high yet.

i seen this in person and its lookin very nice ... glad to see you guys have worked on the regulator

you guys already know to put me on a list of people that would like to test and help out the best i can man

also that powersupply kit i got from you top knotch man

"All the new circuitry" amounts to changing some one-cent component values from the original spec, and adding about twency cents in components for the altered LED driver. It'll take a lot more than that to change the estimated $20. Right now that's still an estimate, but one we really hope to hit. The only real question remaining is heatsink cost, which I just sent an updated spec out on Thursday so I don't know yet what a price would be.

Sidehack, how much do you estimate will be the Compac's price with all the new circuitry involved?

and that is where it belongs.  well  at least in my opinion I would  vote it into your museum.

Nope, it's going in our mining hardware museum.

my thought was what sidehack was thinking, it is history in making i wanted to own a part of it, and when Beastlymac expands on his little museum idea, i'd donate it. None the less, it's treasure, to all involved.

I would throw in a bid for that, who wouldn't want a cool prototype from the early days of mining?  Just a thought, maybe you could make some kind of a charity auction out of it.  Or maybe the funds could go to support core dev(seeing as the btc foundation just imploded).


That 675mv line looks sexy as hell!

Text? No, he only gives his phone number to friends.

Ha! You can't just text Novak? You guys crack me up.

Hurry up with the big boards!! I kid, but seriously. I have not had any new gear in a long time. The withdrawals are getting bad.

Yeah, the pins on that regulator chip are quarter-millimeter wide with quarter-millimeter spacing. I don't know how you pulled that off. And then there were the traces running between pads on 0603 parts. Ridiculous.

I'm already working out in my head how to build up a power-metering USB port I can run off an external supply. I'll throw it together Saturday afternoon and get some numbers out of it. I think I'm gonna need to beef up heatsinking on the ASIC though, before stress-testing too much. That crappy little sink that's on it, especially being surrounded by cables and jumpers, won't do 3W by itself.

Also, Novak, if you beat me in to the shop tomorrow the thing's running on my bench and the LEDs turned out sexier than I could have hoped. Take a gander. The drive circuit was also pretty simple. The RF pulses were so short you couldn't even tell anything was lighting up, so I used a double FET inverter with an RC delay on the second gate to hold it closed longer and extend the LED pulse a bit. I was afraid I'd have to use a comparator circuit but it works well enough with the FET gate threshold and such. I didn't scope the RF pulse but it's on the order of 50mS; my driver extends that to probably 150-200mS.

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.



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

--
novak

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. 

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.

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...


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!

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.