<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 ?
<DocScrutinizer>
nope
<wpwrak>
why not ?
<DocScrutinizer>
because of the weight ;-D
<wpwrak>
huh ?
<wpwrak>
it's the standard 500 mA USB, not the power plant edition with 500 MA ;-)
<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
<DocScrutinizer>
do the math - you won't get happy with inductors for that
<DocScrutinizer>
use a resistor plus a huge buffer C
<DocScrutinizer>
even better use a PTC
<DocScrutinizer>
aka recovering fuse
<wpwrak>
hmm, resistor isn't so nice. that rail's voltage is already a bit marginal
<DocScrutinizer>
then you better use a dedicated regulator rather than some inductor that won't help
<DocScrutinizer>
or a FET
<wpwrak>
so maybe just more buffer. currently, there's 220 uF. usb standard recommends 120 uF.
<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 ...
<DocScrutinizer>
eeew
<DocScrutinizer>
FET based current limiter
<DocScrutinizer>
maybe even with softstart
<wpwrak>
hmm, let's see if such things exist ready-made ...
<wpwrak>
ah, NTC ?
<DocScrutinizer>
PTC NTC I always confuse them
<DocScrutinizer>
you want a short protection anyway
<wpwrak>
hmm PTC would be fuse type where as NTC would be inrush limiter
<wpwrak>
not sure what happens when we short USB. the short just gets passed to the external power supply. M1 itself doesn
<wpwrak>
t try to control that rail
<wpwrak>
DocScrutinizer: i'll copy my mail to the milkymist list to you. is joerg@openmoko.org still you principal mail address ?
<DocScrutinizer>
yes
<DocScrutinizer>
btw there's no such thing like NTC inrush limiter, that's always fuse type
<DocScrutinizer>
well, theoretically this would work, but it's never really used
<wpwrak>
of course, ~ 10 R isn't a lot. lemme check ...
<DocScrutinizer>
I only know those for 220V~ when efficiency and voltage drop aren't really an issue
<wpwrak>
yeah, all these seem to be designed for mains. not sure how nice they are at lower voltages
<wpwrak>
simulation says that 10 Ohm ought to help if the power supply has halfway decent load regulation
<wpwrak>
simulation also
<wpwrak>
says that my calculation of the resulting voltage across the caps is wrong. grmbl.
<wpwrak>
weird. Cport*Vbefore^2/2 = (Cport+Cdevice)*Vafter^2/2 should hold, no ? assuming no losses to ESR, etc.
<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)
<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 ?
<DocScrutinizer>
wpwrak: nothing wrong basically with chaning LDOs
<DocScrutinizer>
wpwrak: assuming no losses to ESR is quite simplifying thing when you have no series R like a fuse
<DocScrutinizer>
wpwrak: in that case the ESR of both buffer C (host and attached dongle) will matter in your equation
<DocScrutinizer>
you basically get:Â Â GND --- C1-esR1 --x-- esR2-C2 --- GNDÂ Â where one C is charged and other one discharged and you're probing at (x)
<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 :)
<DocScrutinizer>
a big C1 tends to have a big ESR1, and a smaller C2 vice versa
<DocScrutinizer>
you get conservation of charge, not energy
<wpwrak>
apparently, reaction time is around 2 us, which ought to be sufficient to avoid the worst
<DocScrutinizer>
Coloumb is the magic word
<DocScrutinizer>
no Ws
<wpwrak>
shouldn't both be conserved ? (energy = J)
<DocScrutinizer>
so your "^2" is wrong I think
<DocScrutinizer>
no, the energy gets converted to heat in ESR etc
<wpwrak>
hmm, right, Q doesn't have a ^2
<wpwrak>
wait, in a perfect cap, no energy goes to ESR
<wpwrak>
so where does it go ?
<DocScrutinizer>
nowhere :-)
<DocScrutinizer>
the model is wrong
<DocScrutinizer>
in a near to ideal real setup the energy gets emitted by a monster EMP
<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
<wpwrak>
the switch is open. i charge C1 to V1 and discharge C2.
<DocScrutinizer>
in the end you're moving electrons, do that fast enough and watch gamma ray escape
<wpwrak>
now the energy in my system is C1*V1^2/2
<DocScrutinizer>
right
<wpwrak>
next, i close the switch. now both caps become one large cap of C = C1+C2
<wpwrak>
(they're parallel)
<DocScrutinizer>
:nod:
<DocScrutinizer>
electrons move from C1 to C2 in *zero* time, right?
<wpwrak>
doens't matter. i look at the system after they've arrived
<wpwrak>
hmm. i'm not sure if that enters this ideal model
<DocScrutinizer>
btw CERNÂ Â is for sure highly interested in your setup
<DocScrutinizer>
;-D
<wpwrak>
;-)
<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
<wpwrak>
can i use a friend of maxwell's demon ? :)
<wpwrak>
alas, doesn't have the answer to my puzzle
<wpwrak>
lemme calculate this with Q instead of E
<wpwrak>
hah, pretty exactly what the simulation says, too
<DocScrutinizer>
wpwrak: if this charge exchange between Cs would work, we could build PSUs without inductors and with 100% efficiency
<wpwrak>
oh, again, i was assuming an ideal model. of course you have parasitic effects in real life
<DocScrutinizer>
right, like electromagnetism created by electron flow
<DocScrutinizer>
aka parasitary inductance
<DocScrutinizer>
ESR
<DocScrutinizer>
there is no complete correct model that could eliminate these
<DocScrutinizer>
the simpler your model, the more even properties of plain wires matter
<wpwrak>
but if, for modeling purposes, we assume perfect caps and superconducting wires. then the energy lost would go into what ... entropy ?
<DocScrutinizer>
build a model of an ideal battery shorted by an ideal wire, what do you get?
<DocScrutinizer>
right: nonsense :-D
<wpwrak>
okay, but you can do a limes :)
<DocScrutinizer>
into an EM field, as you build an oscillator this way
<wpwrak>
also my simulation has an ESR of 100 mOhm, or qucs would puke :) but it doesn't really affect the result
<wpwrak>
and where does the EM field go after things have stabilized ?
<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.
<DocScrutinizer>
it dissipates in the environment
<DocScrutinizer>
you build a LC resonator with your ideal wire and Cs, and it will oscillate and thus emit RF
<DocScrutinizer>
as even an ideal wire is an inductor
<wolfspra1l>
C-Keen: the normal discharge rate for a li-ion cell is about 1% / day I think
<wpwrak>
C-Keen: in theory, it shouldn't. not sure about practice, though :) (i keep all my bens tethered)
<wolfspra1l>
the cell may be worn out substantially after a while, reducing what is 100%
<C-Keen>
yep I usually do too, that's why I did not noticed
<wolfspra1l>
also there may be a software issue, that is the NanoNote is actually not fully off and drawing from the battery
<DocScrutinizer>
I bet all my bucks on the latter
<C-Keen>
I am not running the latest image, I should upgrade anyway
<wolfspra1l>
if you want to investigate this more, you need experiments ;-)
<DocScrutinizer>
or LEDs
<DocScrutinizer>
;-D
<wolfspra1l>
second battery, or even two new ones, charge both fully, leave one in the device, one outside, etc.
<C-Keen>
the led besides the usb plug cannot be controlled by the kernel, can it?
<DocScrutinizer>
I always found it rather reassuring to have an LED on each and every power rail :-)
<wolfspra1l>
unfortunately the Ben battery charging status cannot be measured or read well, complicating any fact finding
<DocScrutinizer>
and they are cheap, giving good data at as little as 0.5mA
<DocScrutinizer>
well, alas I have no Ben to retrofit those LED
<DocScrutinizer>
and nobody asked me to design them into the original board
<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
<DocScrutinizer>
to save that 30ct/PCBA
<DocScrutinizer>
the layout is same price no matter if footprints for LED are there or not
<DocScrutinizer>
s/layout/PCB/
<wpwrak>
still seems overkill to me :)
<DocScrutinizer>
hah
<wpwrak>
but i guess *i* would have routed those USB host signals somewhere, even if only test points :)
<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
<DocScrutinizer>
;-P
<DocScrutinizer>
labour*
<DocScrutinizer>
labour at labor
<DocScrutinizer>
now you know why my OM business card said "HW & synergy"
<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
<DocScrutinizer>
while CR gets flooded with "fsckng Ben cuts thru battery in no time"
<DocScrutinizer>
"batery is crap"
<DocScrutinizer>
"device locks up after few hours of shutdown"
<DocScrutinizer>
"device doesn't boot"
<DocScrutinizer>
"device dead, reflashing only helps for 1 day"
<DocScrutinizer>
etc
<DocScrutinizer>
and honestly, how much overkill are a few FOOTPRINTS
<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 :)
<DocScrutinizer>
no the footprints are exactly as free as are months of headbanging due to obscure power drain
<wpwrak>
at OM, shouldn't the biz card have said "HW & sarcasm" ? :)
<DocScrutinizer>
absolutely for free
<DocScrutinizer>
the sarcasm comes for free :-D
<C-Keen>
uhm, what are you arguing about :) and why? :)
<wpwrak>
C-Keen: just banter ;-)
<DocScrutinizer>
C-Keen: indicator LEDs on Ben's power rails
<DocScrutinizer>
I'd have insisted on getting at least footprints on PCB for those
<C-Keen>
I understood that
<DocScrutinizer>
btw I hope tomorrow you'll "lose me"
<DocScrutinizer>
to ST-Ericsson
<DocScrutinizer>
R&D labs LTE etc
<DocScrutinizer>
conveniently located here in my town
<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
<wpwrak>
DocScrutinizer: (STE) interview or already siging ceremony ?
<wpwrak>
sigNing
<DocScrutinizer>
interview
<wpwrak>
(0R in gta02) ah well ...
<wpwrak>
best of luck then ! though we'll hate to "lose" you
<DocScrutinizer>
well, I may still be available at what's night hours in my TZ
<DocScrutinizer>
or even beter get a job involving doing lots of IRCing maybe ;-D
<DocScrutinizer>
maybe I could push for more community oriented work?
<DocScrutinizer>
(doubt that, it's ST-E after all)
<DocScrutinizer>
guess they don't care much about "community"
<DocScrutinizer>
aah, and thanks wpwrak
<wolfspra1l>
DocScrutinizer: wow, great news - good luck!
<DocScrutinizer>
thanks :-D
<wolfspra1l>
I'm not worried we loose you, you are indestructible