2011-08-27 00:01 <DocScrutinizer> feels like eventually having a glance at m1 schematics
2011-08-27 00:02 <DocScrutinizer> if anybody would bother tossing over a URL of a pdf
2011-08-27 00:08 <wpwrak> DocScrutinizer: here it is: http://milkymist.org/mmone/rc3_schematics.pdf
2011-08-27 00:08 <DocScrutinizer> coming to think of it, I'd probably nevertheless design this circuit with a beta>150 NPN emitter follower, 4k7 from emitter*pin23 to GND, and a 2 pcs 220k divider for base, from AVDD to AVSS
2011-08-27 00:09 <DocScrutinizer> oh, and of course anothe decoupling C from emitter to pin23
2011-08-27 00:09 <wpwrak> phew. getting complex :)
2011-08-27 00:10 <DocScrutinizer> nah, bom=5 pcs
2011-08-27 00:10 <DocScrutinizer> you save one R of your divider though
2011-08-27 00:10 <wpwrak> i think the ~50 pF cap is something we could get into rc4. anything else is scary.
2011-08-27 00:10 <DocScrutinizer> make 4
2011-08-27 00:10 <wpwrak> *grin*
2011-08-27 00:11 <larsc> DocScrutinizer: http://www.analog.com/static/imported-files/rarely_asked_questions/groundingADCs.ppt
2011-08-27 00:11 <DocScrutinizer> advantage: idependence of actual Z if chip'
2011-08-27 00:11 <DocScrutinizer> s input
2011-08-27 00:12 <DocScrutinizer> single point of failure (transistor)
2011-08-27 00:12 <DocScrutinizer> cheap to fix
2011-08-27 00:12 <DocScrutinizer> inherent ESD-prot
2011-08-27 00:14 <DocScrutinizer> high effective input Z allows for clean design of the input devider and input Z, and also allows proper RF rejection
2011-08-27 00:14 <DocScrutinizer> just IF I were to design this detail ;-D
2011-08-27 00:15 <DocScrutinizer> wtf is this URL above?
2011-08-27 00:18 <wpwrak> "AGND and DGND [...] should be connected together [...] Even if the data sheets suggests otherwise!" touche ! ;-)
2011-08-27 00:19 <wpwrak> (ADCs ppt) good stuff
2011-08-27 00:23 <DocScrutinizer> well, I've never seen a datasheet suggesting to use a bead to connect AGND and DGND. But it's also probably not correct to simply use one plane for AGND and DGND
2011-08-27 00:23 <DocScrutinizer> raher use 2 planes and connect them at one point, next to power supply
2011-08-27 00:23 <wpwrak> DocScrutinizer: (the beads) they were basically a misunderstanding that propagated into various subsystems. we've already fished one out of the video section a while ago. now there's another one in audio.
2011-08-27 00:24 <DocScrutinizer> ouch
2011-08-27 00:24 <DocScrutinizer> never place beads into ground (exception that confirms the rule: headset jack, for antenna purposes)
2011-08-27 00:26 <DocScrutinizer> anyway for your usecase you shouldn't bother at all about noise
2011-08-27 00:26 <wpwrak> yeah, it did interesting things to the respective codecs. luckily, no permanent damage.
2011-08-27 00:26 <DocScrutinizer> so for this particular usecase a common groundplane is just fine
2011-08-27 00:29 <wpwrak> i have my doubts about all the ground going to peripherals. M1 connects to a lot of stuff. i think it would be safer to have things like MIDI, DMX, maybe also audio galvanically separated from the rest.
2011-08-27 00:29 <DocScrutinizer> anyway, time for a burger. cya
2011-08-27 00:29 <wpwrak> food sounds like a good idea :)
2011-08-27 00:29 <wpwrak> contemplates his options
2011-08-27 00:30 <DocScrutinizer> yeah, for a stage device connected to a lot of peripherals, galvanic separation is a must, at least for audio
2011-08-27 00:31 <DocScrutinizer> stage environment can do to a device without bead in gnd what even your home stereo did to a device with bead ;-D
2011-08-27 00:31 <DocScrutinizer> buzzword ground loops
2011-08-27 00:32 <wpwrak> i think a few unpleasant lessons will be learned
2011-08-27 00:32 <wpwrak> but right now, nobody is in the mood to do major changes
2011-08-27 00:33 <DocScrutinizer> you'd either use the floating gnd+opamp design I initially mentioned here, or you (better) use a real oldfashioned trafo
2011-08-27 00:33 <DocScrutinizer> mantelwellenfilter
2011-08-27 00:33 <wpwrak> are there actually galvanic audio separators available as separate devices ?
2011-08-27 00:33 <DocScrutinizer> audio separator trafo
2011-08-27 00:33 <DocScrutinizer> yes sure
2011-08-27 00:34 <steve|m> good ol' DI-boxes will work as well, everyone on stage has them ;)
2011-08-27 00:34 <wpwrak> heh ;-)
2011-08-27 00:34 <DocScrutinizer> DI-box *is*  a audio separator trafo
2011-08-27 00:34 <wpwrak> good. maybe wolfgang can source one in china for a few femtocents
2011-08-27 00:34 <DocScrutinizer> steve|m: and everyone on stage knows why :-D
2011-08-27 00:35 <steve|m> DocScrutinizer: sure
2011-08-27 00:35 <DocScrutinizer> ground loops are ubiquitous
2011-08-27 00:36 <wpwrak> i also wonder how things like DMX (lighting control) treat their ground
2011-08-27 00:36 <wpwrak> my guess would be "not well"
2011-08-27 00:36 <DocScrutinizer> audio via DI, all else is one digital GND level
2011-08-27 00:36 <DocScrutinizer> floating
2011-08-27 00:37 <DocScrutinizer> for DMX devices - uneducated guess of me
2011-08-27 00:38 <wpwrak> on stage (well, VJ desk), you may have video in, video out, MIDI, and DMX connected
2011-08-27 00:38 <DocScrutinizer> btw seems nobody knows what "DI" means
2011-08-27 00:38 <wpwrak> there's also ether, but that's probably rarely used there. USB is for things like keyboard and mouse, so no ground issues.
2011-08-27 00:38 <DocScrutinizer> wpwrak: yeah, and each of those possibly has its own mains fuse and another phase
2011-08-27 00:38 <wpwrak> so what does it mean ? :)
2011-08-27 00:39 <wpwrak> (other phase) exactly :)
2011-08-27 00:39 <DocScrutinizer> I dunno :D
2011-08-27 00:39 <steve|m> direct injection
2011-08-27 00:39 <wpwrak> especially light should be able to get pretty distributed
2011-08-27 00:39 <DocScrutinizer> video out equipment is light here too
2011-08-27 00:40 <wpwrak> yeah, also goes a distance
2011-08-27 00:40 <DocScrutinizer> video in probably less of a problem
2011-08-27 00:40 <wpwrak> something must be :)
2011-08-27 00:41 <DocScrutinizer> audio yes. Another system with antenna on the roof and looong speaker cables, and lots of power pulling up the neutral wire of mains
2011-08-27 00:42 <wpwrak> well, let's hope people approach the big and complex installations slowly and with care :)
2011-08-27 00:42 <DocScrutinizer> so connect GND of all these systems and feel happy when there's not Ampere flowing thru it
2011-08-27 00:43 <DocScrutinizer> then delta-I protectors kick in and everything dark :-D
2011-08-27 00:44 <wpwrak> *grin*
2011-08-27 00:44 <DocScrutinizer> or you got no delta-I breakers in your fuse box, and see some of your equipment literally sending smoke signals
2011-08-27 00:45 <DocScrutinizer> (I witnessed such mishaps)
2011-08-27 00:46 <wpwrak> sweet. let's add some extra ground planes ;-)
2011-08-27 00:46 <DocScrutinizer> 6mm^2
2011-08-27 00:46 <DocScrutinizer> ;-P
2011-08-27 00:47 <DocScrutinizer> wire of course
2011-08-27 00:48 <wpwrak> copper bars linking all the external grounds :)
2011-08-27 00:48 <DocScrutinizer> that's what I meant by 6mm^2
2011-08-27 00:49 <kristianpaul> https://secure.wikimedia.org/wikipedia/en/wiki/All_Watched_Over_by_Machines_of_Loving_Grace  also video link http://www.youtube.com/watch?v=C17zbTTYVME
2011-08-27 00:49 <DocScrutinizer> well a 6sqmm wire is not yet a bar, but almost
2011-08-27 00:49 <DocScrutinizer> waves, for good
2011-08-27 00:50 <wpwrak> hopes you'll return one day :)
2011-08-27 00:50 <DocScrutinizer> post me a URL linking to m1 schem eventually, please
2011-08-27 00:50 <wpwrak> DocScrutinizer: i already did: http://milkymist.org/mmone/rc3_schematics.pdf
2011-08-27 00:51 <DocScrutinizer> hope I'll get to move my arse one day
2011-08-27 00:51 <DocScrutinizer> ooh
2011-08-27 00:51 <wpwrak> DocScrutinizer: a view of the pcb is here: http://downloads.qi-hardware.com/people/werner/m1/tmp/front.png
2011-08-27 00:51 <DocScrutinizer> you did?
2011-08-27 00:51 <wpwrak> and here: http://downloads.qi-hardware.com/people/werner/m1/tmp/back.png
2011-08-27 00:51 <DocScrutinizer> indeed you did
2011-08-27 00:51 <wpwrak> hehe :)
2011-08-27 00:55 <DocScrutinizer> WTF L1 ?!
2011-08-27 00:56 <DocScrutinizer> yeah, and L3
2011-08-27 00:56 <wpwrak> seems that L1 has already become 0R
2011-08-27 00:57 <wpwrak> my L3 is now, too :)
2011-08-27 00:57 <wpwrak> some 80+ will follow soonish, i guess
2011-08-27 00:57 <DocScrutinizer> WTF R11
2011-08-27 00:57 <wpwrak> ;-)))))
2011-08-27 00:58 <wpwrak> and C10
2011-08-27 00:58 <wpwrak> hah, but that's what wolfson do, too
2011-08-27 00:59 <DocScrutinizer> C24
2011-08-27 00:59 <DocScrutinizer> C10 is kinda OKish
2011-08-27 00:59 <DocScrutinizer> R11 is NOT
2011-08-27 01:00 <DocScrutinizer> C10 is actually for creating some sort of floating GND for CD input
2011-08-27 01:00 <wpwrak> no clue what R11 does
2011-08-27 01:01 <DocScrutinizer> same a chokes in GND do
2011-08-27 01:01 <wpwrak> C24 is do-not-place
2011-08-27 01:01 <DocScrutinizer> I see
2011-08-27 01:01 <DocScrutinizer> nevertheless, the pin is NC
2011-08-27 01:01 <wpwrak> CD in has probably never been tested
2011-08-27 01:01 <DocScrutinizer> I bet
2011-08-27 01:02 <wpwrak> yeah, dunno what C24 was supposed to do
2011-08-27 01:02 <DocScrutinizer> as this R11 spoils stereo separation, at very least
2011-08-27 01:02 <wpwrak> ah, that would make sense ;-)
2011-08-27 01:03 <DocScrutinizer> L1 (without a buffer C at chip side) is *evil*
2011-08-27 01:07 <wpwrak> well, if the codec has very constant consumption ... ;-)
2011-08-27 01:07 <wpwrak> anyway, i think L1 is 0R
2011-08-27 01:08 <DocScrutinizer> C122 R47 next button1,2,3 and no ESD prot on signal lines. I'm concerned
2011-08-27 01:09 <wpwrak> hmm, fun items
2011-08-27 01:10 <DocScrutinizer> I'd make D4 a zener maybe, 2V2
2011-08-27 01:12 <DocScrutinizer> \o/ two zeners in parallel: D14, D15
2011-08-27 01:12 <DocScrutinizer> usually a sure blow
2011-08-27 01:12 <wpwrak> hmm ?
2011-08-27 01:14 <wpwrak> dunno what the idea is. maybe one as backup for the other. in case there's some problem (soldering or burned-to-open)
2011-08-27 01:15 <wpwrak> of course, if the plan is that they share the current, then that probably won't go so well ..
2011-08-27 01:15 <wpwrak> at least not in a parallel way :)
2011-08-27 01:16 <DocScrutinizer> C168 C170 and the Rs, are they needed?
2011-08-27 01:16 <DocScrutinizer> or can C167 C169 take over
2011-08-27 01:18 <DocScrutinizer> VBUS on J16 J20 could probably use a fuse
2011-08-27 01:19 <wpwrak> at least C168 looks a little odd indeed
2011-08-27 01:19 <wpwrak> VREF in an SDRAM ? wow. never saw that.
2011-08-27 01:23 <wpwrak> hmm, dunno what to make of it. the data sheet doesn't recommend anything like this
2011-08-27 01:24 <DocScrutinizer> I'd spend some OVP/ESDprot for VGA RGB
2011-08-27 01:26 <DocScrutinizer> L19 
2011-08-27 01:27 <DocScrutinizer> OK, done
2011-08-27 01:27 <DocScrutinizer> what was that, a burger? ;-D
2011-08-27 01:27 <DocScrutinizer> heads out
2011-08-27 01:35 <wpwrak> grabs empanadas, beer
2011-08-27 05:17 <rjeffries> from my perspective, therte's a lot to like about this board. I agree, it is not "real" yet, but seems to be getting there. If they can sell it for z$50 it will be quite attractive. I do wish it had a small AVR on board to provide a bunch of i/o
2011-08-27 05:17 <rjeffries> http://hackaday.com/2011/08/26/raspberry-pi-might-not-be-vaporware/
2011-08-27 05:18 <rjeffries> the other missing piece of the puzzle is a microsd (aka 8:10) slot. It REALLY mneeds removable memory.
2011-08-27 08:09 <wolfspraul> kyak: I read about your misfortune with a 'g' key - too bad. how is the key behaving now?
2011-08-27 09:08 <lekernel> docScrutinizer: L1 (without C) and R11 come from the LM4550 "typical application" schematics from National Semiconductor
2011-08-27 09:10 <lekernel> as surprising as it may seem, NS actually recommended L1 be added without capacitor for the first revision of the LM4550
2011-08-27 09:11 <lekernel> they rolled it back for the B revision (that's why it's 0) and other codec manufacturers do not recommend it either
2011-08-27 09:11 <lekernel> http://www.national.com/an/AN/AN-1528.pdf
2011-08-27 09:11 <lekernel> "12) L1 was required with the LM4550, but is not required or recommended with the LM4550B."
2011-08-27 09:15 <lekernel> wpwrak, all modern SDRAMs (2000+) have VREF *g*
2011-08-27 09:28 <lekernel> and it needs to be precise and free from noise; some sources recommend not sharing it across chips
2011-08-27 09:28 <lekernel> anyway we'll definitely not risk a SDRAM disaster on 160 boards just to spare 2 resistors and 2 capacitors
2011-08-27 09:40 <lekernel> I don't think the zeners in parallel are that bad: their response curve is not square, they have positive temperature coefficient (so the zener that dissipates the most has its voltage increasing until the other zener takes over), and the circuit needs to operate for only a few seconds (and when the user has done a mistake) until the fuse trips
2011-08-27 09:41 <lekernel> FYI those zeners can take 6.5A for 1s each
2011-08-27 09:55 <kyak> wolfspraul: (the g key) it's not so good.. i haven't tried Werner's suggestion to use a piece of paper (didn't have time and a proper screwdriver)
2011-08-27 09:56 <kyak> wolfspraul: speaking about hardware issues, the USB port has become pretty loose over the time
2011-08-27 09:56 <kyak> i guess i use it much more frequently than average Ben user
2011-08-27 09:57 <wolfspraul> most likely :-)
2011-08-27 09:57 <kyak> when i take Ben in hands while it's connected to USB, it is a common that it would disconnect
2011-08-27 09:57 <wolfspraul> probably just mechanically wearing out
2011-08-27 09:58 <kyak> yep. And a lot of blindly sticking at night :)
2011-08-27 09:58 <wolfspraul> that's why we need to go all rf in the future. not much we can do about it.
2011-08-27 10:00 <kyak> if you are talking about some external rf card, this would cause problems, too
2011-08-27 10:01 <kyak> because one would have to put it in and take it out every time he puts Ben in a pocket
2011-08-27 10:05 <wolfspraul> oh no, of course I mean integrated
2011-08-27 10:05 <wolfspraul> people underestimate how bad connectors are
2011-08-27 10:05 <wolfspraul> 'bad' in terms of life expectancy, for example
2011-08-27 10:06 <wolfspraul> well, keep us posted, even if your Ben shows signs of aging now. what can we do. 'g' key, usb connector, hinge probably also getting loose over time...
2011-08-27 10:22 <kyak> wolfspraul: i read about the problem with hinge, but luckily it works well for me so far
2011-08-27 10:23 <kyak> another thing i have in mind are silicone "legs" of Ben
2011-08-27 10:23 <kyak> there is only one left out of four :)
2011-08-27 10:24 <kyak> even though i glued it myself some time ago
2011-08-27 10:24 <kyak> they get ripped off - i guess they just have a small area of connection
2011-08-27 10:25 <kyak> and probably the last thing are those dust particles under the screen glass - but we discussed it already
2011-08-27 10:36 <Jay7> compare to 'legs' of Zaurus SL-C3x00: http://www.penguin.cz/~utx/zaurus/bottom.jpg
2011-08-27 10:49 <wolfspraul> yes the feet, true. nice zaurus picture btw!
2011-08-27 10:49 <wolfspraul> the zaurus feet are a little longish, not sure whether that helps or not. I think all feet that are only glued will show the same problem.
2011-08-27 10:50 <wolfspraul> as usual Apple seems to be the one with the most thoughtful approach, I have to take my old MacBook apart to see how they did those roundish feet so well...
2011-08-27 10:50 <wolfspraul> my Asus notebook is loosing the glued feet left and right
2011-08-27 10:50 <wolfspraul> I'm worried the same will happen to the 4 feet on m1, although roh chose a very expensive 3M thingie
2011-08-27 10:51 <wolfspraul> just checked my 2.5 yr old Asus notebook - 1 out of 4 feet left :-)
2011-08-27 10:58 <Jay7> wolfspraul: at least I've not seen reports about lost Z's feet :)
2011-08-27 10:59 <Jay7> lost stylus is more frequently reported :)
2011-08-27 10:59 <Jay7> btw, that's not my photo
2011-08-27 10:59 <Jay7> :)
2011-08-27 11:00 <Jay7> I'm looking at Z's feets now
2011-08-27 11:00 <Jay7> they are at least half inside back panel
2011-08-27 11:00 <Jay7> looks like just glued
2011-08-27 11:00 <wolfspraul> sure, glued
2011-08-27 11:01 <wolfspraul> lemme try some surgery on my old macbook :-)
2011-08-27 11:01 <wolfspraul> for one the feet on the macbook are curve-shaped so they provide very little attack surface from the side
2011-08-27 11:02 <Jay7> that's the point (little attack surface from the side)
2011-08-27 11:04 <wolfspraul> even better
2011-08-27 11:04 <wolfspraul> there's a hole in the plastic, below you can see some round piece of metal, probably part of what holds the inside together
2011-08-27 11:05 <wolfspraul> then the rubber/plastic is melted into the hole, so it doesn't sit on a flat surface but first fills the hole, and then only the topmost part stands out (and is curve shaped all around)
2011-08-27 11:07 <kyak> wolfspraul: seems like you will be sued for the feet of Ya :)
2011-08-27 11:07 <wolfspraul> nah
2011-08-27 11:07 <kyak> i think the key is the surface area
2011-08-27 11:08 <kyak> Zaurus feet's surface is larger than Ben's
2011-08-27 11:08 <kyak> so it holds glue better due to a bigger point of contact
2011-08-27 12:00 <Jay7> kyak: this is true too
2011-08-27 12:01 <Jay7> lower attack surface, larger glue surface, deeper hole
2011-08-27 12:25 <DocScrutinizer> lekernel: (NS actually recommended L1) maybe that chip version had a buffer C on another pin? I don't understand the rationale anyway || ( just to spare 2 resistors and 2 capacitors) full ACK, I just asked IF it can be shared. If it's deprecated, then OK || (Zeners) If those Zeners have positive coefficient then it's semi-safe. I'm not sure if some Zeners have negative coefficient though. For the purpose I had no doubts. Anyway if the 
2011-08-27 12:25 <DocScrutinizer> power dissipation is the limiting factor, 2 Zeners in series would be the better choice: half the voltage, double the max I. || Thanks for comenting on it :-D
2011-08-27 12:25 <wpwrak> lekernel: (sdram and vref) yeah, we live in crazy times :)
2011-08-27 12:25 <lekernel> lower voltage zeners have negative temperature coefficient
2011-08-27 12:26 <lekernel> the temperature dependence of zener diodes is actually made of two semiconductor effects, one with a positive temperature coefficient and one with a negative coefficient
2011-08-27 12:27 <lekernel> the effect with the positive coefficient takes over when the zener voltage increases
2011-08-27 12:28 <DocScrutinizer> well, I learnt it doesn't always work, the hard way :-D
2011-08-27 12:36 <DocScrutinizer> but yes, low voltage zeners are usually made of simple diodes in series, while 'real' zeners are a special diode operating in inverse direction. Only those have a virual diode antiparallel so that they work as zener or as diode depending on direction of current. So for my suggestion regarding D4(?) - the one antiparallel to optocoupler's LED - to use a zener there was implying a higher voltage zener properties that's probably not 
2011-08-27 12:36 <DocScrutinizer> available for 2V2
2011-08-27 12:41 <DocScrutinizer> s/virual/virtual/
2011-08-27 12:58 <DocScrutinizer> yes, according to datasheet a 1B5339 5V6 Zener shall have a positive coefficient of ~0.5..2mV/°C. Even for 5V0 Zeners of that series (if they existed) the diagram (figure 2) seems to suggest they could have negative coefficient. Sideeffect of protection acainst inverse polarity aka true Zener with low Vf confirmed
2011-08-27 13:00 <lekernel> why do you want to use a zener for MIDI? I don't understand ...
2011-08-27 13:00 <lekernel> in one direction, the optoisolator conducts, in the other direction (which shouldn't happen anyway) the diode conducts
2011-08-27 13:00 <lekernel> I actually don't know why that diode is there, but the MIDI standard recommends it... for optoisolator protection maybe
2011-08-27 13:01 <wpwrak> lekernel: for overvoltage, it may make sense. so you burn the diode, not the coupler.
2011-08-27 13:02 <lekernel> both are cheap and easily replaced
2011-08-27 13:03 <lekernel> also, you'd need to dissipate a bit in the resistors for such things to happen :-)
2011-08-27 13:05 <wpwrak> yes, the R may burn first. dunno how "quick" LEDs are in comparison. i've had both go up in flames quite rapidly. (in controlled experiments :)
2011-08-27 13:10 <DocScrutinizer> a LED will degrade while a parallel Zener of correct voltage could dissipate a lot more energy and keep realy high Vf away from the optocoupler. It was a suggestion if we are free to reconsider and source a nice matching part for D4
2011-08-27 13:10 <DocScrutinizer> and yes, purpose is OVP from midi, obviously
2011-08-27 13:13 <DocScrutinizer> lekernel: midi standards suggest this D4 protective diode for a good reason: LEDs are *very* sensitive to both ESD and OV in reverse direction, and they have a really poor Vr_MAX
2011-08-27 13:15 <DocScrutinizer> the more expensive high-power LEDs and laser LEDs even come with built-in ESD
2011-08-27 13:16 <DocScrutinizer> which - as always - isn't sufficient for "real life", when e.g. the LED is driven via a connector to the outer world that can inject all sorts of surges
2011-08-27 13:17 <DocScrutinizer> on-chip ESD frequently is only for safe handling in fab, not to meet and ESD model
2011-08-27 13:17 <DocScrutinizer> s/and/any/
2011-08-27 13:20 <DocScrutinizer> in general I agree with the rationale that those optocouplers are cheap and easy to replace. I've done this so many times :-D And I always appreciated when they were DIL-8 and on a socket
2011-08-27 13:31 <DocScrutinizer> (btw same for the TL074(?) OPAMPS frequently used in consumer grade audio mixer table inputs. Blow frequently due to missing DI box ;-P and often are on socket from fab)
2011-08-27 16:18 <qi-bot> [commit] Werner Almesberger: labsw/: first draft layout complete (master) http://qi-hw.com/p/wernermisc/80084df
2011-08-27 17:25 <lekernel_> DocScrutinizer: thanks for your comments.
2011-08-27 18:59 <DocScrutinizer> yw
2011-08-27 19:02 <DocScrutinizer> lekernel_: one more question: why are the SDRAM ADR lines terminated by shared resistor networks (R71-90), while DQ lines have individual termination (R93-133)?
2011-08-27 19:03 <lekernel_> they're all terminated with the same resistors
2011-08-27 19:04 <lekernel_> I didn't use resistor packs because when soldering them manually it's easy to short circuit pins if you are not very careful
2011-08-27 19:04 <lekernel_> ah, no, sorry
2011-08-27 19:04 <DocScrutinizer> that's not the point of my question
2011-08-27 19:05 <lekernel_> that's just because address pins and command pins are shared on both SDRAM chips, and the simpler single-resistor solution met signal integrity requirements
2011-08-27 19:06 <DocScrutinizer> r71-90 are used shared while R93-112 is left chip, R114-135 right chip
2011-08-27 19:06 <lekernel_> the whole thing acts like a single 32-bit SDRAM chip
2011-08-27 19:06 <DocScrutinizer> oooh, the data lines differ on both chips?
2011-08-27 19:06 <lekernel_> yes
2011-08-27 19:07 <lekernel_> the point of having two chips is to get more bandwidth
2011-08-27 19:07 <DocScrutinizer> indeed, didn't notice - nevermind
2011-08-27 21:38 <wpwrak> DocScrutinizer: Q: assuming an opto-coupler i want to protect against a negative input (i.e., on the diode side), if i don't want to use a diode to short it, like M1 does, but instead have it fail open, what can i use ? one objective is that the minimum voltage for operating the optocoupler should be as low as possible, i.e., about 1.4 V.
2011-08-27 21:39 <wpwrak> DocScrutinizer: i thought of using a P- or N-MOSFET, but their gates don't handle much abuse (only up to +/- 20 V) in the ones i found
2011-08-27 21:40 <wpwrak> DocScrutinizer: i think i can operate the opto-coupler up to 30 V (with series resistor) before anything blows
2011-08-27 21:42 <wpwrak> DocScrutinizer: ah yes, other goals are very little activation current and generally a wide input voltage range. (this is for lab use - shouldn't be too picky about what it's being fed, be able to resist some abuse, and of course not be too complicated/expensive :)
2011-08-27 21:42 <wpwrak> DocScrutinizer: any ideas ?
2011-08-27 21:45 <DocScrutinizer> sorry, I missed to understand your fist post
2011-08-27 21:45 <DocScrutinizer> what's fail open?
2011-08-27 21:45 <wpwrak> DocScrutinizer: open = no current
2011-08-27 21:46 <wpwrak> DocScrutinizer: as opposed to the diode in M1, which just shorts the input if reversed
2011-08-27 21:46 <wpwrak> DocScrutinizer: e.g., if someone connects something fragile, i don't want to fry it
2011-08-27 21:47 <DocScrutinizer> so you want an input that has galvanic separation, operates at <=1.4V, at 1mA, doesn't draw any current when reversed, and is immune to OV up to 30V any polarity?
2011-08-27 21:47 <wpwrak> i think it will actually work already at ~100 uA :)
2011-08-27 21:47 <DocScrutinizer> wpwrak: well, it not shorts the input, as the diode is behind the 22R
2011-08-27 21:48 <DocScrutinizer> 220R
2011-08-27 21:48 <DocScrutinizer> sorry, I don't get it
2011-08-27 21:48 <wpwrak> yes, but at ~30 V, that would still be a significant current (in my case, I'll use 1 kOhm, but still)
2011-08-27 21:49 <DocScrutinizer> if you say "it will actually work already at ~100 uA" it occurs to me you already got a solution and are asking me to make me happy 
2011-08-27 21:49 <wpwrak> no no .. my solution has no reverse voltage protection yet
2011-08-27 21:49 <wpwrak> the 100 uA path would be forward
2011-08-27 21:50 <DocScrutinizer> sorry, you completely lost me
2011-08-27 21:51 <wpwrak> my opto-coupler should transmit enough current for the MCU input on the other end if driven with ~100 uA at ~1.5 V (if my calculations are right)
2011-08-27 21:52 <wpwrak> (this is not M1, it's something else)
2011-08-27 21:52 <DocScrutinizer> you sound like those "how could I write a letter using firefox" lusers. Either you got a solution that fulfills your requirements, or you asking for a better solution then I don't see how you can say "it works with 100uA already"
2011-08-27 21:52 <wpwrak> "already" referred to the low current, not to the point in time
2011-08-27 21:52 <wpwrak> you wrote 1 mA, i mentioned that 100 uA should do
2011-08-27 21:53 <DocScrutinizer> "should" != " i think it will actually work"
2011-08-27 21:54 <wpwrak> i think "i think" conveys the concept of colloquial "should" quite well :)
2011-08-27 21:54 <DocScrutinizer> sorry, no idea
2011-08-27 21:55 <wpwrak> so, the circuit is as follows: input goes through 1 kOhm/1 W, and into the opto-coupler's LED. on the other side, i have a reasonably sensitive MCU input with a weak pull-up.
2011-08-27 21:56 <wpwrak> all want is a means to cut current to, say, <= 1 mA when the voltage is reversed. at up to ~30 V
2011-08-27 21:56 <wpwrak> cut current through the opto-coupler's LED
2011-08-27 21:59 <wpwrak> first thought was to add a schottky in series, but that would increase the minimum voltage at which all this works. and i want it to be sensitive
2011-08-27 22:01 <wpwrak> the objective of the whole exercise is to have a galvanically-separated input i can use to probe digital signals in the lab. that may be a power rail, some 3.3 or 5 V logic, or maybe something 1.8 V-ish. the more i can do, the better
2011-08-27 22:02 <wpwrak> it may also be something not exactly at the respective rails, e.g., an output that's already loaded
2011-08-27 22:02 <DocScrutinizer> use an optocoupler opamp, get a 2nd PSU for the input
2011-08-27 22:03 <wpwrak> that brings me to yet another objective: simple and cheerful ;-)
2011-08-27 22:03 <DocScrutinizer> you can do sth like 0.1..200V with it
2011-08-27 22:03 <wpwrak> yes, that would be great. but too complex.
2011-08-27 22:03 <DocScrutinizer> I want a pony
2011-08-27 22:03 <wpwrak> indeed :)
2011-08-27 22:04 <DocScrutinizer> opto-opamp us as simple as it gets, for your requirements
2011-08-27 22:05 <DocScrutinizer> s/us/is/
2011-08-27 22:05 <DocScrutinizer> you can have Z of several 10..100kR, and after that it's easy to clamp any OV
2011-08-27 22:06 <wpwrak> i want the input side to be unpowered
2011-08-27 22:06 <DocScrutinizer> won't fly
2011-08-27 22:06 <wpwrak> so there's no component that can simply cut if the voltage is reversed ? sort of like an ideal diode
2011-08-27 22:07 <DocScrutinizer> no
2011-08-27 22:07 <DocScrutinizer> not if you also want OVP
2011-08-27 22:10 <wpwrak> okay, two components. one to cut, the other to protect it from harm. in fact, three in total: the series resistor to limit the current, the X to cut reverse voltage, and maybe a third to protect X from ESD
2011-08-27 22:11 <DocScrutinizer> OV not ESD. For "ideal diodes" OV starts at maybe 10V
2011-08-27 22:11 <DocScrutinizer> it won't fly
2011-08-27 22:11 <wpwrak> if you go over the maximum design voltage (~30 V in my case), all bets are off anyway. but 30 V should be enough for this kind of use.
2011-08-27 22:11 <DocScrutinizer> I already pondered multi-component solutions
2011-08-27 22:12 <wpwrak> hmm, so the shorting diode is the only reasonable choice ?
2011-08-27 22:12 <wpwrak> or a big warning label that you'll get to swap the coupler if voltage is reversed and above TTL levels (the coupler can handle 6 V)
2011-08-27 22:13 <DocScrutinizer> even then your claims of 0.1mA@1.5V and safe up to 1mA@30V is hard to achieve
2011-08-27 22:14 <wpwrak> the MCU needs only about 50 uA. the current transfer ratio of the coupler is 50% or better. thus 100 uA should do, no ?
2011-08-27 22:14 <DocScrutinizer> no, as it needs a certain minimum current to operate afaik
2011-08-27 22:15 <DocScrutinizer> even then I don't see how you get from 0.1mA@1.5 to 1@30
2011-08-27 22:16 <wpwrak> no no, 30 mA at 30 V
2011-08-27 22:16 <DocScrutinizer> also if the coupler needs 1.5V Vf, how much is your series R then?
2011-08-27 22:16 <wpwrak> 1 kOhm. the coupler needs 1.4 Vf(max)
2011-08-27 22:17 <wpwrak> the data sheet only shows If down to 1 mA :-(
2011-08-27 22:17 <DocScrutinizer> toldya
2011-08-27 22:17 <DocScrutinizer> that's what I had in my storage about optocouplers
2011-08-27 22:18 <wpwrak> if i extrapolate (looks linear in the area), then i may be good up to ~200 uA
2011-08-27 22:19 <wpwrak> i'll have th measure what it really can do
2011-08-27 22:20 <DocScrutinizer> sounds like a "let's see if it works with components of this production week" design
2011-08-27 22:21 <wpwrak> well, i have a bit of tolerance. of it works reliably at 0.5 mA, i'm happy
2011-08-27 22:21 <DocScrutinizer> btw I've actually seen couplers that produced false positives when you opened the case and light fell on them
2011-08-27 22:21 <wpwrak> ;-)))
2011-08-27 22:21 <wpwrak> yes, i've heard of that
2011-08-27 22:21 <wpwrak> mine have black plastic, that's already a bit reassuring
2011-08-27 22:22 <DocScrutinizer> those were in a design similar to yours, ultralow currents, very high impedances
2011-08-27 22:24 <DocScrutinizer> those had as well black plastic
2011-08-27 22:26 <wpwrak> don't buy those made by murphy inc. ;-))
2011-08-27 22:26 <DocScrutinizer> now imagine you got them on a frequency generator for a 2MW rotary current motor
2011-08-27 22:26 <wpwrak> well, the thing will have a reasonably light-tight case
2011-08-27 22:26 <wpwrak> ;-)))
2011-08-27 22:28 <DocScrutinizer> will make it safe until you walk by with a gas lantern or petromax, anything that has a incandescent mantle
2011-08-27 22:28 <wpwrak> its output should eventually be able to handle mains (not in this version yet, though), so a bare board wouldn't be so nice ;-)
2011-08-27 22:29 <wpwrak> ok, 5 mm aluminium bar over the couplers ;-)
2011-08-27 22:29 <DocScrutinizer> the more I'd try not to drive it to the limits of the components, rather make it safe and with sufficient headroom in all parameters
2011-08-27 22:29 <wpwrak> and an emergency ration of liquid nitrogen somewhere :)
2011-08-27 22:29 <wpwrak> yes, of course
2011-08-27 22:30 <DocScrutinizer> limits to the microscopic end are as unsafe a ground to stand as are ABS MAX rathings
2011-08-27 22:31 <wpwrak> the intended voltage range for the couplers is about 1.8 V - 15 V. minimum current at 1.8 V about 0.5 mA. i'd like to be compatible with 1.8 V logic.
2011-08-27 22:32 <DocScrutinizer> hmm, that sounds somewhat more sane
2011-08-27 22:32 <DocScrutinizer> still I don't know of any couplers designed for <1mA
2011-08-27 22:33 <DocScrutinizer> doesn't mean you might not be able to find some
2011-08-27 22:33 <wpwrak> the relays (two of them) will be able to do more. eventually, i want to be able to switch mains. but i need various different components for this to be even remotely safe.
2011-08-27 22:35 <DocScrutinizer> the sanest method is to exploit random 50kHz and a small siferrit transformer to get sth like 3V@1mA galvanically separated power supply for the input stage 
2011-08-27 22:36 <wpwrak> i'll just measure what the coupler can do. if the curve can be extrapolated ... fig. 5, page 11 of http://media.digikey.com/pdf/Data Sheets/Lite-On PDFs/LTV-8x6.pdf
2011-08-27 22:36 <wpwrak> ... then i should hit the zone where If*CTR is too low around 200-300 uA
2011-08-27 22:36 <DocScrutinizer> you quite usually mustn't extrapolate curves of datasheets
2011-08-27 22:37 <wpwrak> it looks nice and flat for almost half the range before ;-)
2011-08-27 22:37 <wpwrak> but yes, there can be surprises :)
2011-08-27 22:38 <DocScrutinizer> there WILL be surprises, as the fab doesn't trst for those extrapolated component properties
2011-08-27 22:38 <DocScrutinizer> test*
2011-08-27 22:38 <wpwrak> (transformer) waaaay to complex :)
2011-08-27 22:39 <wpwrak> of course. but that doesn't mean they're per se unusable. lot of things are operated at points well outside what the data sheets specifies. sometimes, there's not even a sane way to avoid this ...
2011-08-27 22:39 <DocScrutinizer> yeah, that's what they told me about getting and keeping a pink pony
2011-08-27 22:40 <wpwrak> you should have asked for a turquise one. or just a standard unicorn :)
2011-08-27 22:42 <wpwrak> anyway, measurements will show if extrapolation looks reasonable or not. and no reverse voltage protection then.
2011-08-27 22:43 <wpwrak> the chip are cheap anyway :)
2011-08-27 22:43 <DocScrutinizer> I'd go for a max373 or whatever they are called, and then build proper signal converter in front of that
2011-08-27 22:43 <DocScrutinizer> even more "complex", but proper
2011-08-27 22:44 <DocScrutinizer> in this context signal converter could mean sth as simple as a transistor with a huge resistor on the basis
2011-08-27 22:45 <DocScrutinizer> to protect the whole thing against OV
2011-08-27 22:46 <wpwrak> naw, disposable optocouplers will be the solution
2011-08-27 22:46 <DocScrutinizer> if 100k or 1M is still too low an impedance for reverse polarity case, you can use a schottky then
2011-08-27 22:46 <DocScrutinizer> meh
2011-08-27 22:50 <wpwrak> okay, thanks ! now i think i know what i'm up against
2011-08-27 22:50 <wpwrak> next stop: sockets :)