#qi-hardware IRC log for Saturday, 2014-05-03

nicksydneyjust want to check if what i'm thinking is current....if datasheet says the backlight max current is 40mA and voltage is 20 which means it is 0.81W than I can supply 24v but 25mA which is 0.6W ... am I correct ?02:56
nicksydneyjust want to check if what i'm thinking is correct....if datasheet says the backlight max current is 40mA and voltage is 20 which means it is 0.81W than I can supply 24v but 25mA which is 0.6W ... am I correct ?02:56
wpwrakthere's a new CAD on the block: http://solvespace.com/index.pl02:57
nicksydneyhope my question is making sense :)02:57
wpwrakdesigned for windoze, but apparently somewhat runnable on linux as well02:57
nicksydney"somewhat runnable" is not comforting :)02:57
wpwrakit seems that people are working on improving runnability issues :)02:58
wpwrakif your display says 20 V, 24 V could be dangerous. check the "absolute maximum ratings". they tell you where the transition between comfort zone and black smoke happens02:59
wpwrakand what happens if your power supply can't provide the current the display wants depends on the display :) maybe it'll just get a little darker03:00
wpwrakyou can imagine the display as a resistor: for 40 mA at 20 V, it would be 500 Ohm. if you can only supply 25 mA, you'll get 12.5 V. so that's quite low.03:05
wpwrakit may be that it still works, though. since it's a bit more complicated than a resistor :) you can test such things with a lab power supply. just set the voltage to 20 V, current to 25 mA, and see what happens03:06
wpwrakif you intend to operate outside the specification, you also have to make sure you know under what circumstances you'll exceed the limits. e.g., if the display has highly variable consumption depending on content, then you need to make your tests with the "worst-case" content03:07
wpwrakin the case of an OLED, that would be with all the pixels on03:08
nicksydneywpwrak: the datasheet mention this http://postimg.org/image/50km94spd/ so the Forward Voltage is what I was looking at is 20.4v max correct ?04:26
nicksydneyand this is the schematic  http://postimg.org/image/j43fbbaan/ that is used to drive the TFT 04:30
nicksydneythe schematic  has a jumper 25mA and 100mA so assuming 25mA is selected that means it supply 24v with 25mA ... that's very high right ?04:31
wpwrakokay, current-controlled. then you're fine if you set it to 25 mA. the circuit will figure out the rest.04:34
wpwraki assume that the converter is part of your display circuit ? i.e., it's known to work ?04:35
wpwrakbecause it doesn't look quite right. but that may be a labeling problem04:36
nicksydneyit's from another project not mine but trying to get idea from different projects...and this project uses that kind of schematics and yes it does work04:36
wpwrakah, if you're mixing designs you have to be careful04:36
wpwrakwhy not use fairchild's application circuit ?04:37
nicksydneyno not mixing design just trying to learn how other similar project are powering the backlight driver....if i mix i become a rapper than ... hehehee04:37
nicksydneyi was surprised when i saw this design why it supply 24V whereas the datasheet of the TFT being used is 20V04:37
wpwrakmaybe it's for a different display ? 04:38
nicksydneyyes it is for different display...the datasheet i posted is the display that the project is using04:38
nicksydneythe display that i'm goingt o use has different parameters...max is 19v for my display....04:38
nicksydneyso trying to understand how it was used :)04:38
wpwrakin any case, that circuit doesn't control the current through the LEDs. that's why it may be a bit dangerous for your case04:38
wpwrakjust do what fairchild suggest ? :)04:39
nicksydneyi'm using TPS61040 not this chip 04:39
nicksydneylet me paste the datasheet for the TFT i'm going to use04:39
wpwrakthen do what TI say ... it's not that hard ;-)04:40
nicksydneythis is the TFT 5inch datasheet http://postimg.org/image/8oenr8qnd/04:41
nicksydneyit doesn't say MAX but it has the TYP which is 19.2v so i assume that will be the voltage i need to generate via TPS6104004:41
nicksydneywhat you mean by "okay, current-controlled. then you're fine if you set it to 25 mA. the circuit will figure out the rest." ... are you saying that the IC even it outputs 24V and the current via jumper is specified 25mA it knows how much current to pass ?  04:44
wpwrakif the IC's output is defined by the current, the voltage varies depending on the current04:49
wpwrak24 V would then be the maximum voltage, but what's really controlled is the current. and yes, current is what matters most with LEDs, not the voltage04:50
nicksydneyso logically for that schematic if the voltage was not 24V but say 35V but the current is 25mA the backlight for the corresponding TFT will be ok or it will smoke ?04:52
wpwrakjust design your power supply circuit for 40 mA. if the chip also has a settable maximum voltage, set it to 20 V.04:54
wpwrakand design everything else (inductor, etc.) for at least 40 mA and 20 V.04:54
nicksydneyahhhh this  "if the IC's output is defined by the current, the voltage varies depending on the current"  ... click in my head now :)04:56
nicksydneyok thanks it make sense to me now :)04:56
wpwrakhehe :)04:57
nicksydneysomtimes the concept and relationship between voltage and current is not sticking in my head so need an easier explanation :)04:59
nicksydneyupgraded to the latest kicad and now the module in PcbNew is not showing up :(05:08
nicksydneywpwrak: which branch did you use for your kicad ? the latest code is not stable getting lots of crash05:15
wpwrakbzr 4150. almost a year old :)07:15
sb0roh, do you think it's possible to engrave text on a powder-coated aluminum surface by burning the powder coating using a laser cutter, and obtaining a visually good result?13:28
rohsb0: maybe.14:04
rohdunno about powder coating. black anodizing can be made lighter14:04
sb0roh, ok, can I try it at rfa sometime?14:06
rohyeah.. but i do not know if and when i find time14:09
rohi hurt my hand some week ago and work is piling up as we speak ;)14:10
rohif its powder coat and not anodized we need to check what kind of plastic it is/was. one cannot laser anything with cloride in it14:11
roheh chlorine14:11
wpwraki;m sure the chlorine won't mind its liberation. "Free Chlorine !" :)14:16
wpwrakbtw, just had an idea regarding biometric authentication. with the advances in the field of induced pluripotency, i wonder if it could become feasible to use cloning to get at someone's biometric markers.14:20
rohtrue. but our lungs and machines mind.14:22
rohchlorine destroys machines. -> anything which contains it => no go.14:23
wpwrakDocScrutinizer51: question: am i right assuming that making a test fixture that produces a variable field roughly resembling a human finger making controlled movements would be fairly simple ? e.g., without moving parts or other fancy components ?21:57
wpwrak(for production testing of the capacitive sensor)21:57
nicksydneyso good to be able to use the old version of kicad .. all the footprints works again :)22:38
wpwrakwhat happened with the current version ? random crashes ? or something more specific ?22:39
nicksydneyrandom crashes and also the footprint menu changed a lot ... now the way it works you need to specify the footprint .mod file as each parameter23:04
nicksydneywith the old version you can just select all .mod files and automatically it is added23:05
nicksydneytoo much work with the new version23:05
wpwrakah, i just add them to the .pro, with vi23:09
nicksydneytoo lazy to do all that better focus on the design for now :)23:13
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