2011-11-14 04:28 <wpwrak> DocScrutinizer: btw, if you had some USB host port to supply and wanted to make sure inrush current of the devices doesn't kill your 5 V rail, would you consider planting a bead/inductor in the path ?
2011-11-14 04:29 <DocScrutinizer> nope
2011-11-14 04:32 <wpwrak> why not ?
2011-11-14 04:32 <DocScrutinizer> because of the weight ;-D
2011-11-14 04:32 <wpwrak> huh ?
2011-11-14 04:33 <wpwrak> it's the standard 500 mA USB, not the power plant edition with 500 MA ;-)
2011-11-14 04:33 <DocScrutinizer> honestly you'll not find a inductor large enough, and even if you would, you won't want to place it into that power rail
2011-11-14 04:33 <wpwrak> it's for this kind of critters: http://downloads.qi-hardware.com/people/werner/m1/rst/m1-atusb.png
2011-11-14 04:34 <wpwrak> or this: http://downloads.qi-hardware.com/people/werner/m1/rst/m1-hhkb.png
2011-11-14 04:35 <DocScrutinizer> do the math - you won't get happy with inductors for that
2011-11-14 04:36 <DocScrutinizer> use a resistor plus a huge buffer C
2011-11-14 04:36 <DocScrutinizer> even better use a PTC
2011-11-14 04:37 <DocScrutinizer> aka recovering fuse
2011-11-14 04:37 <wpwrak> hmm, resistor isn't so nice. that rail's voltage is already a bit marginal
2011-11-14 04:38 <DocScrutinizer> then you better use a dedicated regulator rather than some inductor that won't help
2011-11-14 04:38 <DocScrutinizer> or a FET
2011-11-14 04:38 <wpwrak> so maybe just more buffer. currently, there's 220 uF. usb standard recommends 120 uF.
2011-11-14 04:40 <wpwrak> the dedicated regulator has the problem that there's nothing for it to drop :) in case you haven't guessed, it's the evil milkymist power supply again. with reliance on the external supply to provide a nice 5 V ...
2011-11-14 04:45 <DocScrutinizer> eeew
2011-11-14 04:45 <DocScrutinizer> FET based current limiter
2011-11-14 04:45 <DocScrutinizer> maybe even with softstart
2011-11-14 04:46 <wpwrak> hmm, let's see if such things exist ready-made ...
2011-11-14 04:48 <wpwrak> ah, NTC ?
2011-11-14 04:49 <DocScrutinizer> PTC NTC I always confuse them
2011-11-14 04:49 <DocScrutinizer> you want a short protection anyway
2011-11-14 04:54 <wpwrak> hmm PTC would be fuse type where as NTC would be inrush limiter
2011-11-14 04:55 <wpwrak> not sure what happens when we short USB. the short just gets passed to the external power supply. M1 itself doesn
2011-11-14 04:55 <wpwrak> t try to control that rail
2011-11-14 05:01 <wpwrak> DocScrutinizer: i'll copy my mail to the milkymist list to you. is joerg@openmoko.org still you principal mail address ?
2011-11-14 05:02 <DocScrutinizer> yes
2011-11-14 05:03 <DocScrutinizer> btw there's no such thing like NTC inrush limiter, that's always fuse type
2011-11-14 05:04 <DocScrutinizer> well, theoretically this would work, but it's never really used
2011-11-14 05:07 <wpwrak> they explicitly sell them as such :) http://www.epcos.com/inf/50/db/icl_09/ICL__B57153__S153.pdf
2011-11-14 05:07 <wpwrak> http://search.murata.co.jp/Ceramy/image/img/w_hinm/L0760E.pdf
2011-11-14 05:10 <wpwrak> of course, ~ 10 R isn't a lot. lemme check ...
2011-11-14 05:17 <DocScrutinizer> I only know those for 220V~ when efficiency and voltage drop aren't really an issue
2011-11-14 05:21 <wpwrak> yeah, all these seem to be designed for mains. not sure how nice they are at lower voltages
2011-11-14 05:22 <wpwrak> simulation says that 10 Ohm ought to help if the power supply has halfway decent load regulation
2011-11-14 05:22 <wpwrak> simulation also 
2011-11-14 05:23 <wpwrak> says that my calculation of the resulting voltage across the caps is wrong. grmbl.
2011-11-14 05:27 <wpwrak> weird. Cport*Vbefore^2/2 = (Cport+Cdevice)*Vafter^2/2 should hold, no ? assuming no losses to ESR, etc.
2011-11-14 06:03 <wpwrak> wolfspraul: as joerg has pointed out, with an inductor, he'd worry about weight ;-) (because it would have to be so big to have the desired effect)
2011-11-14 06:57 <wpwrak> DocScrutinizer: ah, and what do you think of chaining LDOs ? e.g., when you have one with only a limited input range. is it okay to put it behind one that brings down the input voltage a bit ? or would you try to avoid such a scenario ?
2011-11-14 07:16 <qi-bot> [commit] Xiangfu Liu: nanonote-files without console option make /dev/console un-readable (master) http://qi-hw.com/p/openwrt-packages/bab2d75
2011-11-14 08:56 <qi-bot> [commit] Xiangfu Liu: csound: make some progress (master) http://qi-hw.com/p/openwrt-packages/75ee508
2011-11-14 12:38 <DocScrutinizer> wpwrak: nothing wrong basically with chaning LDOs
2011-11-14 13:20 <DocScrutinizer> wpwrak: assuming no losses to ESR is quite simplifying thing when you have no series R like a fuse
2011-11-14 13:21 <DocScrutinizer> wpwrak: in that case the ESR of both buffer C (host and attached dongle) will matter in your equation
2011-11-14 13:24 <DocScrutinizer> you basically get:  GND --- C1-esR1 --x-- esR2-C2 --- GND  where one C is charged and other one discharged and you're probing at (x)
2011-11-14 13:24 <wpwrak> (esr) yes, but what worries me there is that the simulation also uses a "perfect" cap. i'd rather have it not disagree with my perfect model that just assumes conservation of energy :)
2011-11-14 13:24 <DocScrutinizer> a big C1 tends to have a big ESR1, and a smaller C2 vice versa
2011-11-14 13:25 <wpwrak> meanwhile, this chap has been proposed as a barrier for inrush current and some more nasties: http://www.diodes.com/datasheets/AP2142A_52A.pdf
2011-11-14 13:25 <wpwrak> it looks quite nice to me
2011-11-14 13:26 <DocScrutinizer> you get conservation of charge, not energy
2011-11-14 13:26 <wpwrak> apparently, reaction time is around 2 us, which ought to be sufficient to avoid the worst
2011-11-14 13:26 <DocScrutinizer> Coloumb is the magic word
2011-11-14 13:26 <DocScrutinizer> no Ws
2011-11-14 13:26 <wpwrak> shouldn't both be conserved ? (energy = J)
2011-11-14 13:26 <DocScrutinizer> so your "^2" is wrong I think
2011-11-14 13:27 <DocScrutinizer> no, the energy gets converted to heat in ESR etc
2011-11-14 13:28 <wpwrak> hmm, right, Q doesn't have a ^2
2011-11-14 13:28 <wpwrak> wait, in a perfect cap, no energy goes to ESR
2011-11-14 13:28 <wpwrak> so where does it go ?
2011-11-14 13:29 <DocScrutinizer> nowhere :-)
2011-11-14 13:29 <DocScrutinizer> the model is wrong
2011-11-14 13:30 <DocScrutinizer> in a near to ideal real setup the energy gets emitted by a monster EMP
2011-11-14 13:30 <wpwrak> wait .. i'm not letting go of conservation of energy just so quickly ;-) i have a closed system, two caps and a switch. the switch has Ron = 0
2011-11-14 13:31 <wpwrak> the switch is open. i charge C1 to V1 and discharge C2.
2011-11-14 13:31 <DocScrutinizer> in the end you're moving electrons, do that fast enough and watch gamma ray escape
2011-11-14 13:32 <wpwrak> now the energy in my system is C1*V1^2/2
2011-11-14 13:32 <DocScrutinizer> right
2011-11-14 13:32 <wpwrak> next, i close the switch. now both caps become one large cap of C = C1+C2
2011-11-14 13:32 <wpwrak> (they're parallel)
2011-11-14 13:32 <DocScrutinizer> :nod:
2011-11-14 13:33 <DocScrutinizer> electrons move from C1 to C2 in *zero* time, right?
2011-11-14 13:33 <wpwrak> doens't matter. i look at the system after they've arrived
2011-11-14 13:33 <DocScrutinizer> moving electrons create radiation
2011-11-14 13:33 <wpwrak> but yes, there is no impedance
2011-11-14 13:34 <DocScrutinizer> you can watch that at CERN
2011-11-14 13:34 <wpwrak> hmm. i'm not sure if that enters this ideal model
2011-11-14 13:34 <DocScrutinizer> btw CERN  is for sure highly interested in your setup
2011-11-14 13:34 <DocScrutinizer> ;-D
2011-11-14 13:34 <wpwrak> ;-)
2011-11-14 13:35 <DocScrutinizer> wpwrak: either your electrons move in *zero* time and emit x-ray/gamma quite a bit, or you explain why they don't move in zero time and you are about to approach a valid model then
2011-11-14 13:36 <wpwrak> can i use a friend of maxwell's demon ? :)
2011-11-14 13:36 <DocScrutinizer> hehe
2011-11-14 13:37 <wpwrak> btw, interesting site: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capcon.html
2011-11-14 13:37 <wpwrak> alas, doesn't have the answer to my puzzle
2011-11-14 13:38 <wpwrak> lemme calculate this with Q instead of E
2011-11-14 13:38 <wpwrak> hah, pretty exactly what the simulation says, too
2011-11-14 13:38 <DocScrutinizer> wpwrak: if this charge exchange between Cs would work, we could build PSUs without inductors and with 100% efficiency
2011-11-14 13:39 <wpwrak> oh, again, i was assuming an ideal model. of course you have parasitic effects in real life
2011-11-14 13:40 <DocScrutinizer> right, like electromagnetism created by electron flow
2011-11-14 13:40 <DocScrutinizer> aka parasitary inductance
2011-11-14 13:40 <DocScrutinizer> ESR
2011-11-14 13:42 <DocScrutinizer> there is no complete correct model that could eliminate these
2011-11-14 13:43 <DocScrutinizer> the simpler your model, the more even properties of plain wires matter
2011-11-14 13:44 <wpwrak> but if, for modeling purposes, we assume perfect caps and superconducting wires. then the energy lost would go into what ... entropy ?
2011-11-14 13:44 <DocScrutinizer> build a model of an ideal battery shorted by an ideal wire, what do you get?
2011-11-14 13:44 <DocScrutinizer> right: nonsense :-D
2011-11-14 13:44 <wpwrak> okay, but you can do a limes :)
2011-11-14 13:45 <DocScrutinizer> into an EM field, as you build an oscillator this way
2011-11-14 13:45 <wpwrak> also my simulation has an ESR of 100 mOhm, or qucs would puke :) but it doesn't really affect the result
2011-11-14 13:46 <wpwrak> and where does the EM field go after things have stabilized ?
2011-11-14 13:46 <C-Keen> speaking of which: is it a known problem that the nanonote discharges itself rather quickly? I never noticed but I forgot mine at a friend's place and got it back 5 days later. the battery was dead.
2011-11-14 13:46 <DocScrutinizer> it dissipates in the environment
2011-11-14 13:47 <DocScrutinizer> you build a LC resonator with your ideal wire and Cs, and it will oscillate and thus emit RF
2011-11-14 13:48 <DocScrutinizer> as even an ideal wire is an inductor
2011-11-14 13:49 <wolfspra1l> C-Keen: the normal discharge rate for a li-ion cell is about 1% / day I think
2011-11-14 13:49 <wpwrak> C-Keen: in theory, it shouldn't. not sure about practice, though :) (i keep all my bens tethered)
2011-11-14 13:49 <wolfspra1l> the cell may be worn out substantially after a while, reducing what is 100%
2011-11-14 13:49 <C-Keen> yep I usually do too, that's why I did not noticed
2011-11-14 13:49 <wolfspra1l> also there may be a software issue, that is the NanoNote is actually not fully off and drawing from the battery
2011-11-14 13:50 <DocScrutinizer> I bet all my bucks on the latter
2011-11-14 13:50 <C-Keen> I am not running the latest image, I should upgrade anyway
2011-11-14 13:50 <wolfspra1l> if you want to investigate this more, you need experiments ;-)
2011-11-14 13:50 <DocScrutinizer> or LEDs
2011-11-14 13:50 <DocScrutinizer> ;-D
2011-11-14 13:50 <wolfspra1l> second battery, or even two new ones, charge both fully, leave one in the device, one outside, etc.
2011-11-14 13:51 <C-Keen> the led besides the usb plug cannot be controlled by the kernel, can it?
2011-11-14 13:51 <DocScrutinizer> I always found it rather reassuring to have an LED on each and every power rail :-)
2011-11-14 13:51 <wolfspra1l> unfortunately the Ben battery charging status cannot be measured or read well, complicating any fact finding
2011-11-14 13:52 <DocScrutinizer> and they are cheap, giving good data at as little as 0.5mA
2011-11-14 13:53 <DocScrutinizer> well, alas I have no Ben to retrofit those LED
2011-11-14 13:54 <DocScrutinizer> and nobody asked me to design them into the original board
2011-11-14 13:55 <DocScrutinizer> though it was absolutely cheap, just needing 20 min of thinking and layout work - you can make them NC any time you want, later on in MP of the million boards
2011-11-14 13:55 <DocScrutinizer> to save that 30ct/PCBA
2011-11-14 13:56 <DocScrutinizer> the layout is same price no matter if footprints for LED are there or not
2011-11-14 13:56 <DocScrutinizer> s/layout/PCB/
2011-11-14 13:57 <wpwrak> still seems overkill to me :)
2011-11-14 13:58 <DocScrutinizer> hah
2011-11-14 13:58 <wpwrak> but i guess *i* would have routed those USB host signals somewhere, even if only test points :)
2011-11-14 13:59 <DocScrutinizer> you're only interested in creating a safe job for you, as investigating those things *without* LEDs for sure costs more in labor than a 1000 boards' LEDs would cost
2011-11-14 13:59 <DocScrutinizer> ;-P
2011-11-14 14:00 <DocScrutinizer> labour*
2011-11-14 14:00 <DocScrutinizer> labour at labor
2011-11-14 14:01 <DocScrutinizer> now you know why my OM business card said "HW & synergy"
2011-11-14 14:03 <DocScrutinizer> with LEDs: get bug reports like "device doesn't shut down, LEDs shine" within 24h after rolling out new firmware. Without: investigate for weeks and months in SW department
2011-11-14 14:04 <DocScrutinizer> while CR gets flooded with "fsckng Ben cuts thru battery in no time"
2011-11-14 14:04 <DocScrutinizer> "batery is crap"
2011-11-14 14:04 <DocScrutinizer> "device locks up after few hours of shutdown"
2011-11-14 14:05 <DocScrutinizer> "device doesn't boot"
2011-11-14 14:05 <DocScrutinizer> "device dead, reflashing only helps for 1 day"
2011-11-14 14:05 <DocScrutinizer> etc
2011-11-14 14:08 <DocScrutinizer> and honestly, how much overkill are a few FOOTPRINTS
2011-11-14 14:08 <wpwrak> i think you misunderstand the economics of work at qi-hw. labour has zero cost. ergo the LEDs are infinitely more expensive than even the most excruciating analysis :)
2011-11-14 14:09 <DocScrutinizer> no the footprints are exactly as free as are months of headbanging due to obscure power drain
2011-11-14 14:09 <wpwrak> at OM, shouldn't the biz card have said "HW & sarcasm" ? :)
2011-11-14 14:09 <DocScrutinizer> absolutely for free
2011-11-14 14:10 <DocScrutinizer> the sarcasm comes for free :-D
2011-11-14 14:10 <C-Keen> uhm, what are you arguing about :) and why? :)
2011-11-14 14:10 <wpwrak> C-Keen: just banter ;-)
2011-11-14 14:10 <DocScrutinizer> C-Keen: indicator LEDs on Ben's power rails
2011-11-14 14:11 <DocScrutinizer> I'd have insisted on getting at least footprints on PCB for those
2011-11-14 14:11 <C-Keen> I understood that
2011-11-14 14:14 <DocScrutinizer> btw I hope tomorrow you'll "lose me"
2011-11-14 14:14 <DocScrutinizer> to ST-Ericsson
2011-11-14 14:15 <DocScrutinizer> R&D labs LTE etc
2011-11-14 14:15 <DocScrutinizer> conveniently located here in my town
2011-11-14 14:19 <DocScrutinizer> wpwrak: you know what'S been overkill? those myriad of 0R on GTA02 which easily could have been surface traces to cut, with two pads to re-solder the cut trace
2011-11-14 14:20 <wpwrak> DocScrutinizer: (STE) interview or already siging ceremony ?
2011-11-14 14:20 <wpwrak> sigNing
2011-11-14 14:20 <DocScrutinizer> interview
2011-11-14 14:20 <wpwrak> (0R in gta02) ah well ...
2011-11-14 14:21 <wpwrak> best of luck then ! though we'll hate to "lose" you
2011-11-14 14:21 <DocScrutinizer> well, I may still be available at what's night hours in my TZ
2011-11-14 14:22 <DocScrutinizer> or even beter get a job involving doing lots of IRCing maybe ;-D
2011-11-14 14:23 <DocScrutinizer> maybe I could push for more community oriented work?
2011-11-14 14:23 <DocScrutinizer> (doubt that, it's ST-E after all)
2011-11-14 14:23 <DocScrutinizer> guess they don't care much about "community"
2011-11-14 14:24 <DocScrutinizer> aah, and thanks wpwrak 
2011-11-14 14:26 <wolfspra1l> DocScrutinizer: wow, great news - good luck!
2011-11-14 14:26 <DocScrutinizer> thanks :-D
2011-11-14 14:26 <wolfspra1l> I'm not worried we loose you, you are indestructible
2011-11-14 18:54 <qi-bot> The build was successfull, see images here: http://fidelio.qi-hardware.com/~xiangfu/compile-log/openwrt-xburst.full_system-11132011-1302/