IRC log for #neo900 on 20161205

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15:27.39ahyckawpwrak, Joerg-Neo900: i would like to add a 0R serie resistor in each line of in SPI bus (RFID/NFC - nfc.sch)
15:27.56ahyckai had some problems in SPI bus between ADCs and FPGA
15:27.57Joerg-Neo900of course, go ahead
15:28.02Joerg-Neo900:-)
15:28.29ahyckaand i had to cut the line to solder 100ohm Resistor in serie
15:28.39Joerg-Neo900ack
15:29.01Joerg-Neo900source side?
15:29.19Joerg-Neo900or termination side, or in the exact middle between the two?
15:29.51Joerg-Neo900I'd think source side, though there are good arguments for termination side too
15:30.22Joerg-Neo900anyway on source side we have waaay more PCB real estate right now ;-)
15:30.34ahyckai put it in source side
15:30.39Joerg-Neo900:-D
15:30.45ahyckabecause i had FPGA and 2ADCs
15:30.48ahycka1 master
15:30.50ahycka2 slaves
15:30.53Joerg-Neo900:nod:
15:30.58Joerg-Neo900usual
15:31.06ahyckain this case, i think doesnt matter
15:31.15ahyckathere is only 1 master and 1 slave
15:31.48Joerg-Neo900it's about driver strength and about ringing aka reflexions
15:32.17Joerg-Neo900reflexions are at ends, driver strength best controlled at master side
15:32.29Joerg-Neo900aiui at least
15:32.45ahyckayes, but SPI is strange, in another board, i had 1 PIC and 2 DDS without any serie resistor, and it works perfectly
15:32.58ahycka1 FPGA and 2 ADCS didnt work without resistor
15:33.00Joerg-Neo900a typical case of "we rather test this in RL and see what works best"
15:33.24ahyckaand i only find some documentation in a book named something like "digital black magic"
15:33.25ahyckaxD
15:33.45Joerg-Neo900what a fitting name :-)
15:34.30ahycka" High-Speed Digital Design: A Handbook of Black Magic, Johnson, Graham 1993"
15:34.30Joerg-Neo900it's about chip pin / driver/receiver circuitry impedances
15:34.32ahyckahere!
15:34.33ahyckahahahahahaha
15:35.13ahyckabut our SPI works at 1MHz!
15:35.20ahyckait's not high frecuency
15:35.24wpwrakour SPIs run at a fairly leisurely speed. 12.5 MHz tops, but more likely around 6.78 MHz, or less
15:35.31ahycka1MHz,5cm length?
15:35.36Joerg-Neo900yeah, not much troubles expected to show up at this
15:35.49ahyckablack magic!
15:37.00Joerg-Neo900anyway, please go ahead adding those, they are actually a oversight not being in there already
15:37.19Joerg-Neo900:-)
15:38.39Joerg-Neo900recalls how happy everybody was to have the programmable driver strength when uSD clock interfered with GPS RX
15:39.57Joerg-Neo900who would have thought that the (iirc) 7th harmonic of clock was *exactly* on GPS frequency
15:40.36Joerg-Neo900nah, must have been like 20th or higher
15:40.48Joerg-Neo900X-P
15:41.32Joerg-Neo900a tiny 4.7pF fixed it pretty good
15:41.55Joerg-Neo900somesuch botch
15:42.13Joerg-Neo900\o/
15:45.49Joerg-Neo900http://wiki.openmoko.org/images/d/dd/Gta02_gps_10pf_rework_sop.pdf
15:47.05Joerg-Neo900http://wiki.openmoko.org/images/5/5b/SOP_for_GPS_capacitor_rework.pdf
15:49.14atkwhen random capacitors and squiggly traces make the difference between broken and working, you know you're dealing with high speed electronics or RF stuff
15:49.33Joerg-Neo900hehe, yes
15:50.08atkEspecially interesting are those high end oscilloscopes which look like someone went into paint and drew random shapes and then made a PCB out of it.
15:50.30Joerg-Neo900this capacitor though wasn't exactly random. I even calculated the capacitance of the chewing gum paper somebody stuck on top of the uSD card which evidently fixed the issue ;-P
15:51.44atkI wonder how someone came up with the idea of putting chewing gum wrapper on the SD card
15:52.18Joerg-Neo900we also tested the effect of the increased capacitive burden on clock slew rate
15:52.50Joerg-Neo900(idea) I don't know, our users were *very* innovative
15:53.04wpwrakpaper = "shielding" :)
15:54.10Joerg-Neo900was a very nasty heissenbug too since it only hit those who actually used their uSD and same time GPS
15:54.51Joerg-Neo900we tested GPS as nauseum and didn't find a problem since none of the engineers had a uSD in their test devices
15:55.00wpwrakwasn't it that the GPS antenna was too close to uSD ?
15:55.02atk( https://youtu.be/1QBFIfKlvHU?t=46m5s - voodoo RF PCB design )
15:55.54Joerg-Neo900atk: preeeeetty
15:58.06atk48:35 - even more weird shapes and squiggles
15:58.24Joerg-Neo90048:30 ROTFL
15:58.32Joerg-Neo900yeah
15:59.34Joerg-Neo900giggles
16:00.00Joerg-Neo900http://wstaw.org/m/2016/12/05/plasma-desktopj17764.png
16:03.03Joerg-Neo900wpwrak: I don't know if the mere distance ever been considered
16:04.08Joerg-Neo900can't be physical distance to the patch antenna since that one was at very top end of device
16:04.39Joerg-Neo900fsckd up EMC
16:05.35Joerg-Neo900the clock simply was allowed to radiate I guess, nobody checked what *exactly* was the failure operation mode
16:06.23Joerg-Neo900maybe a trace was too close to the clock trace, maybe (my fav) the card holder simply acted as antenna
16:08.12Joerg-Neo900but yeah, you can see the GPS antenna plug next to the uSD holder
16:10.28wpwrakyup. rolling out the red carpet for trouble ;)
16:10.31Joerg-Neo900who knows which sort of aerial the gndplane forms with the sleeve shielding of the antenna cable, creating waves propagating along the cable surface to the whole patch antenne and there jumping directly to the antenna patch and into the amp#
16:11.33Joerg-Neo900never forget: *ALL* antennas are dipoles
16:12.33Joerg-Neo900so wiggling with the GNd potential of the patch LNA antenna is exactly same as sening a signal to the antenna patch on top of it
16:12.50Joerg-Neo900sending
16:14.12Joerg-Neo900and a wire shielding gaze running in parallel to the gnd plane it's connected to forms a nice loop antenna by itself
16:15.42Joerg-Neo900s/gaze/braid/
16:16.54Joerg-Neo900reducing the clock driver strength and damping the slew rate further by a 10pF load effectively cured the issue though
16:17.44Joerg-Neo900and simply doing "the right thing" and switch off clock as long as uSD had no operations to perform was the final killer of the issue
16:18.31Joerg-Neo900at least as long as you were not constantly loading map tiles from uSD while using GPS
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17:01.33Joerg-Neo900wpwrak: D1402 IR-LED VBAT n uF bypass capacitor to GND missing
17:04.02Joerg-Neo900also we *might* consider a series R in/from gate to R1410, to reduce slew rate of high current
17:07.16Joerg-Neo900>>In other cases, a maximum slew rate is specified[2] in order to limit the high frequency content present in the signal, thereby preventing such undesirable effects as ringing or radiated EMI<< https://en.wikipedia.org/wiki/Slew_rate
17:09.13Joerg-Neo900we don't need frequency components >500kHz there
17:10.00Joerg-Neo900a very rough guestimate by parasitic capacity of gate and 500kHz is absolutely sufficient for size of series R
17:10.33Joerg-Neo900we have am order of magintude headroom for error to the low side
17:11.23Joerg-Neo900and no hard limits at all to the higher frequency side
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17:59.05ahyckaJoerg-Neo900, could you make me a branch to push my schematics review? (SPI resistors)
17:59.57ahyckai can push/pull in master but i cant checkout a new branch
18:00.16ahyckapush the new branch, I mean
18:03.55wpwrakahycka: that would be for hellekin (joerg doesn't know much about such details of the git setup). i've notified him.
18:04.55ahyckai can ask him
18:05.01ahyckahow900?
18:05.28how900yo ahycka
18:05.57ahyckahi!
18:06.11ahyckacould you make me a branch to push my schematics review?
18:06.27ahyckai can push/pull in master but i can push a new branch
18:06.31how900you have a dedicated branch, let me see... If you ssh git@neo900.org you should have it listed...
18:07.22how900ahycka: it's proto_v2
18:07.43wpwrakhow900: ah, you're already here, good :)
18:08.22ahyckaPTY allocation request failed on channel 0
18:08.22ahyckahello ahycka, this is git@newbie running gitolite3 v3.6.6-2-g8620d5f on git 2.10.0
18:08.22ahycka<PROTECTED>
18:08.23ahycka<PROTECTED>
18:08.23ahyckaConnection to neo900.org closed.
18:08.52ahyckai can't see proto v2 xD
18:11.24how900OK, but if you run:  git push -u origin proto_v2       it should work ahycka
18:11.42how900try this :)
18:13.14wpwrakhow900: is the idea that we'd all work on the proto_v2 branch then ? or would that be ahycka's branch, and we then merge into master ?
18:14.11Joerg-Neo900the latter
18:29.31ahyckawpwrak, by the moment i only add 8 resistor in 2 SPI bus
18:29.48ahyckathe best part is that kicad is plain text! O_O
18:29.51ahyckaaltium is binary
18:30.26ahyckaso, it's impossible compare 2 versions
18:30.38wpwrakahycka: kicad has its share of quirks despite the text, too :)
18:30.48Joerg-Neo900with kicad and Neo900 you get eeschow :-)
18:31.11wpwrakahycka: e.g., if you run ERC, invisible information on all the power symbols changes
18:32.05Joerg-Neo900not terribly useful for git, but for "compare" it's without any competition
18:32.47wpwrakahycka: also, sometimes you redraw a few things, commit, and when you open the sheet again, without making changes, eeschema decides to optimize some wires. so you suddently get a bunch of hard to interpret changes out of the blue. of course, there aren't "real", which eeshow can tell (i.e., no difference)
18:33.17wpwrakJoerg-Neo900: comparing is especially useful with git ;-)
18:33.32Joerg-Neo900with git, but not FOR git
18:34.24wpwrakah, your visual merge. yeah, that would be quite a project :)
18:34.35Joerg-Neo900git diff is (c-)sourcecode centric by design
18:35.05Joerg-Neo900the more so is git merge
18:36.33wpwrakwith kicad, git diff tells you when there's a lot more going on than you expected :)
18:36.46wpwrakand yes, avoid git merge of kicad files
18:36.55ahyckawpwrak rocks!! \o/
18:37.06Joerg-Neo900for very simple changes git merge might work for kicad, but as soon as it gets a tiny bit more involved or kicad messes up, you're lost
18:37.19ahyckaxD
18:37.38wpwrak:)
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19:10.48ceenejust so you know
19:11.06ceenehttp://statics.cuantarazon.com/crs/2016/03/CR_1001836_si_estuviera_encendido_estarias_llorando_amiga_thumb_fb.jpg
19:11.12ceenethis is NOT ahycka
19:11.23Joerg-Neo900oooh
19:11.41ceeneshe still has all ten fingers :)
19:12.03Joerg-Neo900ROTFL
19:12.09Joerg-Neo900good spotting
19:12.21ceenetoo much protection for the eys, she forgot the adamantium gloves
19:12.27ceenes/eys/eyes/
19:12.49ceenewhat was she expecting to happen? exploding capacitors?
19:12.56ahyckahahahahahaha
19:14.18ahyckashe needs a shower cap, i always burn me some hair :(
19:15.22wpwrakceene: (fingers) that's daenerys
19:16.00Joerg-Neo900~dict daenerys
19:16.06wpwrakthe glasses are probably some fashion statement
19:16.33Joerg-Neo900oooh, now even my patter matching got it
19:17.14wpwrak;-)
19:17.45Joerg-Neo900(glasses) useful when soldering on high energy active circuits
19:18.19Joerg-Neo900a 100A@400V arc isn't a joke when you're not wearing glasses
19:18.30ahyckaask ceene!!!!
19:18.30ahyckaxD
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19:18.43Joerg-Neo900I don't need to ask anybody ;-D
19:18.53Joerg-Neo9003 days blind
19:19.13Joerg-Neo900though I wasn't soldering
19:19.13ahyckaceene only 10h
19:19.41Joerg-Neo900mains distribution and a A size battery cell fell in and shorted all 3 phases
19:19.43ahyckawe are playing with high power stage of a lcd...
19:20.00ahyckameasuring voltage
19:20.14ahyckaand...
19:20.19Joerg-Neo900was quite a flash and bang
19:20.20ahyckawhat a beautifull arc!!!
19:20.59ahycka5h watching lights
19:21.11Joerg-Neo900then I had to replace 2 of the 3 63A slowblow fuses
19:21.39Joerg-Neo900and to take care of my eyeballs suffering severe UV light burn
19:22.19ahyckawe were trying to fix the monitor, we killed it :( and monitor went to trash
19:22.30Joerg-Neo900dang
19:22.45Joerg-Neo900as long as nobody got severly injured
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19:23.32ceenenah, it was a loud bang
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19:23.40ceeneanother girl in the lab almost jumped to the ceiling
19:23.57Joerg-Neo900luckily my mishap happened in a feeble 3 room flat distribution
19:24.02ceenebut i kept seeing lights on one eye during the rest of the day
19:24.13ahyckai have to go
19:24.16ahyckacya tomorrow!
19:24.22Joerg-Neo900cya! :-)
19:24.24ceenewe doboth have to go
19:24.35ceenecompany dinner
19:24.48Joerg-Neo900oooh that stuff
19:24.52ceeneif only the boss stayed at home... but then we'd have to pay for our own meal, so at least we've got that :D
19:25.00Joerg-Neo900hehehe
19:25.09ceenewell, cya tomorrow!
19:25.13Joerg-Neo900cya!
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19:40.33wpwrakgrmbl, ahycka isn't "always on"
19:41.07wpwrakceene: i fixed two things, so ahycka will want to merge with "master"
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