libera/#neo900/ Thursday, 2018-06-28

houkimeok, now one needs to check that impedance-matching will be possible without reorganising stuff once properties are known.12:46
houkimeJoerg-Neo900: what is known about neo900 antenna?12:46
houkime*N900 antenna12:46
Joerg-Neo900keep a 2mm "courtyard" around the trace, and contifuous "gnd plane" on next layer? should alliw for sufficent width variability and thus impedance tuning, no?12:49
Joerg-Neo900refer tp N900 bare board layout that irc exposes the trace pn outer layer. And our DR4 or whatever, and rhw oewoewg/layer stacking won't differ that much from N900 either12:52
Joerg-Neo900to* on*12:52
houkime2mm to both sides? (4 mm cross-section) or 2 mm total?13:03
houkime*both sides mean left and right.13:04
houkimejudgung by n900 exploded 2 mm total. ok13:22
houkimeWill try to route 2-mm thick "matched" guys.13:25
houkimeusing only external layers13:25
Joerg-Neo900I'm not very experienced with impmat traces. Usually the PCB house does the details for you13:27
houkimethis is to be expected since they know their materials better.13:28
houkimethe thing on this stage is to eensure it CAN be tuned13:29
Joerg-Neo900I *think* the impedance is determined by dielectric layer thickness till next layer gnd plane, it's properties, clearance of track to "guarding" traces on same layer, and trace width13:29
Joerg-Neo900so make sure you have GND guarding traces, and virtually arbitrary options on trace with and clearance to the guard traces13:31
Joerg-Neo900then I also *think* we will get a Pi-filter (imp transformer) from impmat trace to antenna anyway, and iirc the modem does another one internally13:33
Joerg-Neo900so whatever the impedance of the impmat trace, it gets tuned on both ends and doesn'T really matter in the end. Though we also got the directional coupler and we have no PI-transformers there13:34
houkimewhat's with the vibramotor? is it needed to stay the same model for compatibility also?19:37
houkimehm. doesn't seem so. however, it doesn't seem it can be much improved also.19:56
houkimeit's not like anybody has less tall models.(19:57
houkimeto have a more free placement.19:58
houkimebut i really doubt that for example xiaomi uses 4 mm tall vobramotors!20:02
houkimethey basically have no space for that in the case20:02
houkime(that vibrator messes up stuff a little so i want to see if it is absolutely neccessary)20:03
Joerg-Neo900there are different types of vibra motors. and often they are even integrated into battery. I *fuess* nowadays the coin type is more popular: low height but clumsy formfactor (coin) and relatively large. Not suitable for N900 case anyway20:12
houkimewatched a teardown of xiaomi redmi 4. Funny enough they DO use sth similar to prec-mcro that we wanna use.20:13
houkimehowever they don't mount it in pcb20:14
houkimethey have a hole in pcb and they submerge it there20:14
houkimeand they also have a hole for battery. which is 2/3 of phone surface.20:19
houkimeso everything lives off the remaining 1/3 of the area.20:19
houkimequite impressive how they packed everything20:19
Joerg-Neo900well, looking at snapdragon class of chips, you wonder why they need fabs anymore. Truly somplete System-on-Chip, maybe except RAM and storage20:24
houkimesnapdragon seems like a big security hole though. with system this big and all hidden you never know what one puts inside(20:26
houkimeReally want to try to do sth based on FPGAs.20:27
houkimeso that you have a FPGA modem, an FPGA with zipcpu or sth.20:28
houkimeand all programmable from sth like hackerbus20:28
houkimeor even usb20:28
houkimethere are several bonuses to that. 1st is transparency, and the second one - hey PINS ARE RECONFIGURABLE20:30
houkimethat basically mean that you can tailor this thing for your pcb in terms of pin arrangement20:31
houkimehowever it does comes with a generally slower speed/bigger size.20:32
houkime*does come20:32
houkimethough you can do multiple things on a sigle FPGA which makes it a SOC, so some optimisation possible.20:33
houkimeone main thing though - it is literally impossible for FPGA manufacturer to predict your configuration and code, so a room for trojans is not that big.20:35
houkimeeven if FPGA itself is big.20:36
houkimeyou can't send smb info about you... if you don't even know where the modem is, where antenna is etc.etc.etc.20:38

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