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