#qi-hardware IRC log for Thursday, 2012-02-02

Aylawould USB-over-GPIO be possible?01:03
wpwrakyes :) http://www.obdev.at/avrusb/01:06
Aylaah, I was thinking about a linux driver01:07
Aylastill interesting01:07
whitequarkwpwrak: it's USB device, not host01:08
whitequarkthrough, on one hand, that matters much less for FPGA01:08
whitequarkand on other, I don't know of working, more or less finished USB2.0 cores01:08
wpwrakwhitequark: Ayla didn't specify whether device or host :)01:08
whitequarkI guessed from the context01:09
Aylahost :)01:09
whitequarkah wait, that's not #mm01:09
qi-bot[commit] Xiangfu Liu: pick-pdf script file. thanks jiri.brozovsky (master) http://qi-hw.com/p/openwrt-packages/168c07602:35
qi-bot[commit] Xiangfu Liu: pick-pdf add Version, add -type f to find, exit when no pdf file found (master) http://qi-hw.com/p/openwrt-packages/441bd7e02:35
qi-bot[commit] Xiangfu: nanonote: add bard icon (master) http://qi-hw.com/p/gmenu2x/63f7e5402:37
qi-bot[commit] Xiangfu: nanonote: add pickpdf icon (master) http://qi-hw.com/p/gmenu2x/78b607002:37
whitequarkI strongly advice you to never, ever, try to apply that "one-line" patch on a production server when you are sleep-deprived.13:10
whitequarkit WILL FAIL.13:10
whitequarkcatastrophically.13:10
Action: whitequark has just barely recovered a billing db after such a "patch"13:13
wpwrakDocScrutinizer: a few days ago, you were bragging that one could retrieve bar code data even from under an insane amount of noise. this got me wondering:17:08
wpwrakif you displayed some pattern on a computer/laptop screen and you had a single photo transistor as your sensor. what amount of information could you represent such that you could still decode it when manually moving your sensor over the screen ?17:10
wpwrakthe movement should be "natural" and convenient. so it shouldn't have to be repeated a lot, speed may be imprecise, and you also can't just expect the sensor to be stationary for a long time.17:11
wpwrakwhat i'm looking for the is cheapest and simplest possible method for getting data from a web site via a PC/laptop to a small external device. cheaper and simpler than USB.17:12
mthdoes the external device have a net connection of its own?17:16
mthI mean, do you need to pass only a reference to the data or the data itself?17:16
wpwrakno, doesn't connect to anything17:16
wpwrakfor this to be useful, i need to transfer about 1-2 kB of data. maybe i can segment it into smaller pieces, but 1-2 kB would be ideal17:16
mthyou could use a single location that changes intensity, you it would get 60 bits/second in the best case17:17
wpwraktoo slow17:18
mthbarcodes used on groceries contain a ~10 digit number, that's not a lot of bits either17:18
mthI guess you can scan one or two of those per second17:19
wpwrak(1-2 kB. before compression. compression should be able to reduce this by about 50%.)17:19
mthof course that is old tech, not sure how much you could get with more computation power17:19
mthand it has to be done via the screen? not something like NFC?17:20
wpwrakhmm, let's see how much information is there in the first place. the screen should be 1024xsomething or better. each pixel has, best case, 256 brightness values (let's assume monochrome). so that would be 1 kB of raw data. tight :)17:21
wpwrakit should work with any PC you're likely to encounter17:22
mtha lot of panels don't have 8 bits per pixel17:22
wpwrakyes. "best case" :)17:22
wpwrakmaybe 4 real-life usable bits.17:22
mtherror correction is going to add some overhead as well17:24
mthunless you have so few errors that a CRC is sufficient17:24
mthyou could draw the barcode in some kind of spiral, that might give you more pixels17:25
wpwrakhmm, makes the movement inconvenient17:26
mtha square spiral might not be so bad17:26
wpwrakbuy maybe a U shape or even a zig-zag may work17:26
wpwrak"Z" like "Zorro" ;-)17:27
kristianpaulZ :)17:55
kristianpaulor T17:56
DocScrutinizer51wpwrak: in a minute18:19
DocScrutinizerwpwrak: that'S what the barcodes with always ame width white bars, plus black bars smaller and larger than the white ones are18:34
DocScrutinizeryour clock "PLL" will sync on white, next black bar is either shorter or longer than the last white one18:34
DocScrutinizereven simpler though is playback of a flash movie or sth, that does fullscreen b&w "morse"18:37
DocScrutinizerI.E 50,8N118:38
DocScrutinizer25?18:38
DocScrutinizer10?18:38
larscmy onlinebanking does that kind of thing. if have devices which looks like it has 5 light sensors and data is transfered by holding it in front of a b/w morse kind of flash app18:56
wpwrakhmm. 5 channels. maximum 50 symbols/sec each. not sure how many bits you can encode in the color. let's say 4. that would be 1 kbit. not bad. but still slow.19:09
larschow smart is the device on the other side?19:12
wpwrakAVR class19:13
larschm19:13
wpwraknot quite sure what MCU to take. just has to be cheap :)19:13
larscone think that might allow you to use more brightness levels is to have each valid code word contain one element of min and one of max brightness19:16
wpwrakyes, sort of like bit stuffing. just a little more advanced.19:19
larscturbo codes for ECC19:22
wpwraka manual sweep of a static display would pass over ~800 pixels in ~1-2 seconds. much better data rate than an animation :)19:24
larscbut you need to move at const speed19:26
wpwrakhmm, not overly erratic speed. you can have some clock recovery in the pattern.19:29
DocScrutinizersee above comment of mine19:39
DocScrutinizeryou'll want to use a minimum of 3 px stripes though, for each "bar"19:39
DocScrutinizerso incl clock (white) that's avg min of 7.5px/bit19:41
DocScrutinizerminus CRC19:41
wpwrakwith grey levels, how many bits do you think i could have per bar ?19:42
DocScrutinizerhardly more than 221:02
larscif you use turbo codes at least 421:04
wpwrakhmm, so 2 bits per 3 pixels. let's say in a 600 pixel zone (with places for start and landing), Z shape. so that's 600/3*2*3 bits. 1200 bits, 150 bytes. not much :-(21:04
wpwrakand that's without overhead21:04
LunaVoraxHey everyone!21:27
LunaVoraxHi wpwrak :)21:27
qi-bot[commit] Paul Cercueil: Reinitialize the powersaver timer when a suspend has been detected. (master) http://qi-hw.com/p/gmenu2x/2d81b1322:37
--- Fri Feb 3 201200:00

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