reportingsjr | kristianpaul: an entire pic18 clone? 0.0 wow | 00:38 |
---|---|---|
reportingsjr | that is awesome | 00:38 |
azonenberg | reportingsjr: i got most of the way through a pic12 implementation in an evening | 00:40 |
azonenberg | then abandoned because i realized the architecture was annoyingly inefficient | 00:40 |
azonenberg | i wanted something pipelined | 00:40 |
reportingsjr | azonenberg: how do you do that?? | 00:41 |
azonenberg | verilog on an fpga, obvs | 00:41 |
azonenberg | no, my fab process isnt that advanced ;) | 00:41 |
reportingsjr | haha | 00:44 |
berndj | azonenberg, do you expect diy semi fab to be more suited to small / high speed devices, or to power devices? | 01:02 |
berndj | (once you get over the hump of "works at all") | 01:02 |
azonenberg | berndj: MEMS are the easiest since they're least susceptible to trace metal contamination | 01:02 |
azonenberg | Then power | 01:02 |
azonenberg | because power is easy to do with large process sizes | 01:02 |
berndj | you don't think they're more fussy about impurities, and inhomogeneities thereof? | 01:03 |
azonenberg | Once you get MOS devices to work, no | 01:03 |
azonenberg | in fact, i think big ones would be *less* suscpetible | 01:03 |
berndj | (otherwise you have atrocious SOA) | 01:03 |
azonenberg | a single particle of something is a smallesr portion of the device | 01:03 |
berndj | i hope you're right | 01:03 |
azonenberg | I have no idea, thats just a guess | 01:04 |
azonenberg | MEMS are my field, cmos is a longer term goal | 01:04 |
berndj | yeah - you just don't want that single particle to be more conductive than the rest, and to hog all the current | 01:04 |
azonenberg | Of course | 01:04 |
azonenberg | But the asusmption is that you dont have the particle embedded in the device | 01:04 |
azonenberg | i.e. that it was a bump in photoresist etc | 01:04 |
azonenberg | Also, not much dust is conductive | 01:04 |
azonenberg | its mostly organics (and, more importantly, not stuck very hard to anything) | 01:05 |
berndj | reason i ask is after looking over some opensourceecology.org - and realizing that they're probably dependent on semi power devices more than on any single other semi tech | 01:05 |
azonenberg | i'd be more concerned about metal ions | 01:05 |
azonenberg | getting rid of those is gonna be a pita | 01:05 |
berndj | yeah, i was thinking more about non-uniformities of dopants | 01:05 |
azonenberg | TMAH is a little toxic to be recommending for amateur level fab | 01:05 |
azonenberg | i want to explore use of straight ammonia as a developer | 01:06 |
azonenberg | and dopant difusion isnt really likely to be a problem | 01:06 |
azonenberg | Spin coating gives a very even film of doped SiO2 | 01:06 |
azonenberg | HF etch that away through windows in photoresist | 01:06 |
berndj | where do you draw the line between "calculated risk" and "hey kids, try this at home"? | 01:06 |
azonenberg | then coat with undoped sio2 and diffuse | 01:06 |
azonenberg | berndj: Its different for each person, depends on facilities and experience | 01:06 |
berndj | i get the feeling you just can't get away without dealing with murderdeathkill substances | 01:06 |
azonenberg | And at least MEMS are possible with nothing worse than line-level voltages (120/240 AC), vacuum, KOH, and 3% HF | 01:07 |
berndj | you've already accepted HF, i'm not sure how much worse you can go! | 01:07 |
azonenberg | plus some common solvents | 01:07 |
azonenberg | thats the thing, its extremely dilute hf sold OTC | 01:07 |
azonenberg | bad, but not THAT bad | 01:07 |
azonenberg | CVD is a definite no | 01:08 |
berndj | i was going to ask if there's a material difference between 3% and 30% | 01:08 |
azonenberg | Yes | 01:08 |
azonenberg | Among other things, 3% doesnt fume noticeably | 01:08 |
berndj | but F- diffusing through your skin is one problem | 01:08 |
azonenberg | Yeah, thats the BIG one | 01:08 |
azonenberg | the concentration is 10x lower | 01:08 |
azonenberg | so you have a lot more time to rinse it off | 01:08 |
berndj | you don't ALSO need it to be frothing and desiccating or whatever it does | 01:08 |
azonenberg | before it does any damage | 01:08 |
azonenberg | and there's less F- to neutralize after the fact | 01:08 |
berndj | does HF desiccate stuff? | 01:09 |
azonenberg | I dont think so | 01:09 |
azonenberg | the 3% doesnt at least | 01:09 |
azonenberg | its an aqueous solution :P | 01:09 |
berndj | yeah, there's 97% of pre-desiccated stuff! | 01:09 |
berndj | anyways nothing like fuming H2SO4 | 01:09 |
azonenberg | oh, no | 01:09 |
azonenberg | i want nothing to do with that | 01:09 |
azonenberg | the only acid i'm using in my lab besides 3% hf is concentrated (30%) HCl | 01:09 |
azonenberg | and from what i hear it's much more mild than concentrated h2so4 | 01:10 |
berndj | our high school science teacher turned a blind eye when us A students wanted to "try something"... | 01:10 |
berndj | the H2SO4 + sugar trick was pretty neat | 01:10 |
azonenberg | lol | 01:10 |
azonenberg | in terms of carbonizing organic matter (experimenters included) | 01:10 |
azonenberg | hcl is much less nasty than h2so4 | 01:10 |
berndj | but tbh (and i was younger and stupider then) i did fubar a little bit once - made nitric acid in my lungs! | 01:10 |
azonenberg | um, yeah | 01:11 |
azonenberg | no2 == nasty | 01:11 |
berndj | coughed like hell and i imagine i spat/coughed a trace of blood | 01:11 |
berndj | no >5-minute-term problems though | 01:11 |
azonenberg | Never got a dose nearly that heavy | 01:11 |
berndj | yeah, we did something pretty dumb. neat HNO3 onto some metal shavings i think | 01:12 |
azonenberg | worst i got was some stinging eyes for a few seconds from vapor | 01:12 |
azonenberg | no splashes, had goggles and i think a face shield on | 01:12 |
berndj | goggles? lol | 01:12 |
berndj | how did i ever survive chem class | 01:12 |
azonenberg | This was decapping ICs | 01:12 |
azonenberg | heat sample to 150C on hot plate | 01:12 |
berndj | *which i still need to do | 01:12 |
azonenberg | one drop conc. HNO3 on center | 01:12 |
azonenberg | let it react, grab with tweezers/forceps and swish particles off in acetone | 01:13 |
azonenberg | repeat until die is exposed | 01:13 |
azonenberg | the quantities were small and we were quite careful | 01:13 |
azonenberg | and from now on i have no plans to repeat the experiment outside a fume hood | 01:14 |
berndj | i always forget, acetone has THREE carbons | 01:14 |
berndj | mnemonic: acet-foo is meth-foo + 1, and it's a ketONE | 01:15 |
azonenberg | ochem <shudder/> | 01:16 |
berndj | i've forgotten a lot of it. majored in biochem among others | 01:17 |
Action: azonenberg never even took college chem | 01:17 | |
azonenberg | majored in comp sci :p | 01:17 |
berndj | now THERE is some nasty stuff | 01:17 |
azonenberg | nasty stuff? You want nasty stuff? | 01:18 |
berndj | stuff that'll give you cancer, guaranteed, if you just look at it wrong | 01:18 |
azonenberg | http://en.wikipedia.org/wiki/Chlorine_trifluoride | 01:18 |
berndj | no cheating | 01:18 |
azonenberg | If you get this stuff on you, you wont survive long enough to get cancer :P | 01:18 |
berndj | i like that "hypergolic with no measurable delay" part | 01:18 |
azonenberg | "with test engineers" | 01:19 |
berndj | and ignites asbestos | 01:19 |
azonenberg | Yep | 01:19 |
berndj | of all things | 01:19 |
azonenberg | Probably near the top of materials i do not want to get anywhere near :p | 01:19 |
berndj | i wonder if that's the closest analog to hollywood action movie "acid" pools | 01:20 |
azonenberg | I dont even know what state it's in at room temperature | 01:20 |
azonenberg | is it liquid? | 01:20 |
berndj | i imagine H2SO4 might also work for that | 01:20 |
azonenberg | no, boils at 11.7C | 01:20 |
azonenberg | h2so4 would work, yes | 01:21 |
azonenberg | this stuff would be vapor | 01:21 |
azonenberg | Though if released anywhere near anything organic, it'd look like a ball of fire :p | 01:21 |
azonenberg | This stuff is so nasty that it burns asbestos creating smoke made of HF | 01:21 |
azonenberg | "the operator is confronted with the problem of coping with a metal-fluorine fire. For dealing with this situation, I have always recommended a good pair of running shoes." | 01:22 |
berndj | if HF is the combustion *product*... | 01:23 |
azonenberg | Yeah | 01:23 |
azonenberg | Then the original stuff is even worse | 01:23 |
berndj | maybe you can placate it by feeding it metallic potassium? | 01:23 |
azonenberg | From a significant distance away, i hope? | 01:23 |
berndj | then it will "only" be a fluorine-alkali fire | 01:23 |
berndj | or a nuke: turn the fluorine and chlorine into neon and argon, respectively | 01:24 |
azonenberg | lol | 01:24 |
berndj | they'll be glad the lab only got nuked | 01:25 |
azonenberg | Yeah | 01:25 |
azonenberg | Suffice it to say, thats top on the list of substances i never want to work with | 01:25 |
berndj | i know you're going for MEMS first, but have you got a plan for what dopants to use? | 01:25 |
azonenberg | or even near :p | 01:25 |
azonenberg | Yes | 01:25 |
azonenberg | http://www.emulsitone.com/bsif5x1020.html | 01:25 |
azonenberg | and phosphosilicafilm | 01:25 |
berndj | and p-type? | 01:26 |
azonenberg | P-type is boron | 01:27 |
azonenberg | the link | 01:27 |
berndj | i assume you're working with p-type wafers | 01:27 |
azonenberg | N-type is phosphorus | 01:27 |
azonenberg | http://emulsitone.com/psif3x10_20.html | 01:27 |
berndj | so... some sort of boric acid solution? | 01:27 |
azonenberg | i dont know whats in it | 01:27 |
azonenberg | but the end result is doped SiO2, you etch with HF | 01:28 |
azonenberg | and drive in with thermal diffusion | 01:28 |
berndj | oh and regarding vacuum chambers | 01:28 |
azonenberg | Yeah? | 01:28 |
berndj | i suspect stainless steel is going to be prohibitively expensive | 01:29 |
azonenberg | Was planning to use a glass bell jar for the evaporator | 01:29 |
berndj | what problems could one expect from other steel? | 01:29 |
azonenberg | They outgas more but my guess is that at the pressures we'd be doing it wouldnt matter too much | 01:29 |
berndj | hmm. i guess there's room for stuff to hide in the rust that would invariably build up | 01:29 |
berndj | HF scrubdown! | 01:30 |
berndj | i found my first arc welding experiment harder than i thought | 01:31 |
berndj | major problem: the stick moves in the time that you flip the shade glass down | 01:31 |
azonenberg | Yeah | 01:31 |
azonenberg | I had trouble doign that in class | 01:32 |
azonenberg | i want to try using an auto-darkening lens | 01:32 |
berndj | gas welding was easy by comparison, but no use for making a vacuum chamber | 01:32 |
azonenberg | they basically have a phototransistor that darkens an LCD-based (?) shutter | 01:32 |
azonenberg | reacts in a few microseconds or something | 01:32 |
azonenberg | so the dose of UV etc you get is minimal | 01:32 |
azonenberg | you dont even see the flash | 01:32 |
berndj | yeah, i think i'll have to do that. they're just expensive enough to require a "yes, i really want to do this" decision | 01:32 |
azonenberg | from what i hear nobody professional uses the old-school ones for anything :p | 01:33 |
berndj | yeah, it's fast in darkening, but takes milliseconds to open up again | 01:33 |
azonenberg | Yep | 01:33 |
azonenberg | heck, half a second would be fine for brightening lol | 01:33 |
berndj | i'd just like to either a) understand the mechanism properly, or b) see every last ANSI/ISO mark on it | 01:34 |
berndj | don't want to depend on a battery or solar cell for eye safety | 01:34 |
azonenberg | Lol, i know what you mean | 01:34 |
azonenberg | I think most of them start out at shade 4 ish anyway, so thats a start | 01:34 |
azonenberg | and i think they have a test button | 01:34 |
berndj | hmm, i didn't know that, that would give me more confidence | 01:34 |
azonenberg | in any case i would say buy a good name brand | 01:35 |
berndj | i hear your warning about pressure vessels, but frankly i'd be more scared of a bell jar than of a (well-anchored and made of malleable) steel sphere | 01:36 |
azonenberg | Put a screen over it | 01:36 |
berndj | and yes, shock waves can kill | 01:36 |
berndj | so there'd be a screen too | 01:36 |
azonenberg | also, how big of one are you talking about? | 01:37 |
berndj | big enough for telescope mirrors :) | 01:37 |
azonenberg | If its like 8" across and a foot high, the total energy released in an implosin wouldnt be that bad | 01:37 |
azonenberg | Something big enough for scope mirrors? Oh | 01:37 |
azonenberg | Yeah, that would be problematic if it went poof | 01:37 |
berndj | 8 inch diameter disks would be okay, but ideally i'd like to go bigger | 01:37 |
azonenberg | i meant 8" diameter jar | 01:38 |
azonenberg | which would give you maybe a 4" diameter plating area | 01:38 |
berndj | where are the other 4 inches? | 01:38 |
berndj | surely the glass isn't 2 inches thick... | 01:38 |
azonenberg | no lol | 01:38 |
azonenberg | mounting for the electrodes, etc | 01:38 |
berndj | ah yes. feedthroughs | 01:39 |
azonenberg | as well as the actual sucking hole to evacuate the chamber | 01:39 |
berndj | spark plugs :) | 01:39 |
berndj | i like how ClF3's NFPA 704 says "will not burn" | 01:45 |
berndj | not as a fuel, no! | 01:45 |
azonenberg | Yeah | 01:45 |
azonenberg | But it will oxidize anything in sight | 01:45 |
azonenberg | heck, i think some fluorinating agents can oxidize oxygen to a higher oxidation stat elol | 01:45 |
berndj | heck, oxidizing argon | 01:47 |
azonenberg | XeF2 | 01:48 |
azonenberg | The fact that it exists is scary :p | 01:48 |
berndj | did you ever consider basing a diy semi fab process on anything other than silicon? | 01:49 |
azonenberg | Not really | 01:50 |
berndj | i think the obvious candidates would be ZnO, SiC, CuO | 01:50 |
azonenberg | I am mostly doing mems though | 01:50 |
azonenberg | CuO is a possibility but its a lot harder to work with | 01:50 |
azonenberg | in terms of etching etc | 01:50 |
berndj | is silicon the only game in town for meme? | 01:50 |
azonenberg | Its not, but the existence of KOH for anisotropic etching is a major win | 01:50 |
azonenberg | easy to obtain, not too toxic, and gives you nice slopes or vertical sidewalls | 01:51 |
berndj | eew, i can still smell acetone on my fingers while eating supper | 01:51 |
azonenberg | shouldnt be possible | 01:51 |
azonenberg | the stuff is so incredibly volatile | 01:51 |
berndj | was cleaning a pot (water didn't work) | 01:51 |
azonenberg | must be vapor in the room or something | 01:52 |
azonenberg | but not liquid | 01:52 |
berndj | can't smell it now. maybe some bitterant that i'm confusing for acetone itself! | 01:52 |
azonenberg | Then again i always wear gloves when using acetone or other solvents in nontrivial amounts | 01:52 |
azonenberg | all of that defatting is kinda unpleasant lol | 01:52 |
berndj | NaOH is the bugger there | 01:53 |
azonenberg | naoh is worse, yeah | 01:53 |
azonenberg | turns your fat into soap | 01:53 |
berndj | turns your fingers into soap until you rinse with vinegar | 01:53 |
berndj | ok, so anisotropic etching gives you the high aspect ratios - steep walls. right? if you make, say, a little gear, how do you get it unstuck from the bottom of the pit? | 01:55 |
azonenberg | You'd need to build it on a sacrificial layer | 01:56 |
azonenberg | there are a couple of options | 01:56 |
azonenberg | One is SOI | 01:56 |
azonenberg | and then etch away the oxide | 01:56 |
berndj | sacrificial layer? doesn't that imply CVD? | 01:57 |
azonenberg | Not really | 01:57 |
azonenberg | you can do a lot with evaporation afaik | 01:57 |
azonenberg | you can spin coat sio2 | 01:57 |
azonenberg | its solid-phase deposition | 01:57 |
azonenberg | liquid* | 01:57 |
berndj | hmm. what is the gear made of then - SiO2? i had assumed it would be Si, but i guess that's a spurious assumption | 01:58 |
azonenberg | You could do polysilicon by evaporation or sputtering | 01:58 |
azonenberg | But then you cant do anisotropic etch | 01:58 |
azonenberg | thats something i'm very interested in solving | 01:59 |
azonenberg | but dont yet have an answer to | 01:59 |
berndj | what sort of aspect ratios do you work with? i'm not sure i interpret SEM-grams properly | 01:59 |
azonenberg | Right now? I havent tried going too far | 01:59 |
azonenberg | hoping for 10:1 with KOH on <110> | 01:59 |
berndj | ok, so that steep | 02:00 |
azonenberg | In metal layers, much shallower | 02:01 |
azonenberg | maybe 30-45 degree slope | 02:01 |
azonenberg | since the etch is isotropic | 02:01 |
berndj | and you can't play games with photoresist layers? | 02:02 |
azonenberg | I want to explore something similar to DRIE using multiple photoresist depositions | 02:02 |
azonenberg | spin coat, expose, develop, etch a little | 02:02 |
azonenberg | strip resist | 02:02 |
azonenberg | coat (including sidewalls of undercut area) | 02:02 |
azonenberg | expose, develop, etch again | 02:03 |
azonenberg | it will use a lot of PR but if i do a couple of steps i may be able to improve aspect ratios (assuming i get good alignment) | 02:03 |
azonenberg | But the idea is the same | 02:04 |
azonenberg | DRIE uses an isotropic etch followed by protection of sidewalls | 02:04 |
azonenberg | then repeats the cycle | 02:04 |
azonenberg | so if i did it right i'd get something that looked very much like a Bosch process feature | 02:04 |
azonenberg | make sense? | 02:06 |
azonenberg | Its an idea i've had for a while but havent had time to explore much | 02:06 |
berndj | yeah | 02:07 |
berndj | though full of jargon i'll have to look up :] | 02:07 |
azonenberg | which terms are you talking about? | 02:07 |
berndj | i'm starting with "the" :) | 02:08 |
azonenberg | :p | 02:08 |
azonenberg | Bosch process is http://en.wikipedia.org/wiki/Bosch_process_%28microtechnology%29 | 02:08 |
berndj | DRIE, bosch process (not to be confused with the... is it ammonia synthesis process?) | 02:08 |
azonenberg | SF6 isotropic RIE followed by C4F8 passivation | 02:08 |
azonenberg | DRIE = deep RIE | 02:08 |
azonenberg | http://en.wikipedia.org/wiki/File:Bosch_process_PILLAR.jpg is a nice example | 02:09 |
azonenberg | http://en.wikipedia.org/wiki/File:Bosch_process_sidewall.jpg is a closer view | 02:09 |
azonenberg | note the rounded cutouts on the sidewalls | 02:09 |
azonenberg | Each iteration of the process you do an isotropic etch (which has undercut because its isotropic) and then follow with a passivation process | 02:09 |
azonenberg | the passivation protects sidewalls but is quickly eroded in the bottom of the pit | 02:09 |
berndj | oooh, so DRIE is a bit like FIB but with ions more reactive than Pd / Pt / W / etc? | 02:11 |
azonenberg | Not exactly | 02:11 |
azonenberg | That's RIE in general | 02:11 |
berndj | so... higher energies? | 02:11 |
azonenberg | RIE is generally mildly anisotropic because the ions are being blasted into the wafer from a vertical direction | 02:12 |
azonenberg | But sometimes they bounce and etch sidewalls | 02:12 |
azonenberg | DRIE = deep RIE = higher aspect ratios | 02:12 |
azonenberg | You start out with a short RIE step | 02:12 |
azonenberg | giving you a mostly vertical etch with some undercut | 02:12 |
azonenberg | Then you passivate the entire hole | 02:12 |
azonenberg | You then do more RIE | 02:12 |
azonenberg | The KE of the ions knocks the passivation off the bottom | 02:12 |
azonenberg | but the undercut is slow enough it doesnt attack the passivation much | 02:12 |
azonenberg | since that actino is only chemical and not as mechanical | 02:13 |
azonenberg | Then when you've etched long enough that the passivation is significantly thinned, you re-passivate | 02:13 |
azonenberg | and do another etch step | 02:13 |
azonenberg | and keep going | 02:13 |
azonenberg | My process would be similar except instead of using chemical passivation removed by the KE of the etch | 02:14 |
azonenberg | i'd be using photoresist passivation removed by light shining down the hole during the repeated exposure step | 02:14 |
azonenberg | The profile of the resulting feature would be nearly identical (though given the need for a lot of expose-align steps i dont think more than 4-5 would be feasible in a realistic amount of time) | 02:15 |
azonenberg | But if i just need say a 5x improvement in anisotropy it might help | 02:17 |
berndj | i hope you don't get trouble from sidewall reflection / diffraction | 02:17 |
azonenberg | No idea | 02:17 |
azonenberg | Just ran the idea past a guy i work with - he thinks the alignment will be a PITA but it will likely work | 02:22 |
lekernel | azonenberg: do you know about this? http://www.utwente.nl/tnw/ems/research/cooling/Technology/stirling.doc/ | 09:05 |
lekernel | they look very simple on the schematics :) | 09:05 |
azonenberg | stirling engine? Heard of them | 09:05 |
azonenberg | is this a mems one? | 09:05 |
lekernel | stirling cryocoolers | 09:05 |
lekernel | no | 09:05 |
bart416 | If you run a stirling engine in reverse it works like a heat pump azonenberg | 09:05 |
azonenberg | interesting | 09:05 |
bart416 | They use it for FIR sensors | 09:06 |
lekernel | e.g. http://www.teledynejudson.com/files/pdf/dewars_PB4103.pdf | 09:06 |
azonenberg | yeah, i think i've heard about those | 09:06 |
lekernel | "Temperature Sensor Diode: The ***2N2222*** diode is indicated" | 09:07 |
lekernel | lol? are they talking about a standard 2N2222 transistor? | 09:07 |
lekernel | I built quite a few small radio transmitters with those when I was a kid :-) | 09:08 |
lekernel | didn't know it's apparently good for measuring cryogenic temperatures | 09:08 |
lekernel | I'm very surprised by the apparent simplicity of those devices. I guess the devil is in the details ... | 09:10 |
azonenberg | i knew they used diodes for measuring temperatures | 09:11 |
azonenberg | but i didnt know it worked that low | 09:11 |
azonenberg | the bandgap varies with temperature | 09:11 |
azonenberg | and by extension the forward voltage | 09:11 |
lekernel | well, I can easily try to build one based on bicycle pumps and duct tape and see what happens :-) | 09:12 |
azonenberg | Whats your intended application? | 09:19 |
lekernel | hopefully, reaching cryogenic temperatures at some point :) | 09:36 |
bart416 | azonenberg, VT as temperature reference works right down to absolute zero :P | 09:38 |
reportingsjr | lekernel: a transistor can function as a diode if you tie the base and the collector together | 18:46 |
lekernel | yes | 18:46 |
lekernel | but I was just surprised they use such a common part | 18:46 |
bart416 | It sounds logical to use a common part | 18:46 |
bart416 | Easy to do quality testing | 18:47 |
bart416 | And a 2N2222 is pretty damn reliable | 18:47 |
reportingsjr | yep | 18:50 |
reportingsjr | very easy to source too | 18:51 |
lekernel | yes, but it was never meant to be used as a cryogenic thermometer probe | 18:54 |
lekernel | it's good to know it apparently does a nice job at this | 18:55 |
bart416 | lekernel, name one electronic component that hasn't been abused yet | 18:57 |
bart416 | people have been making point contact transistors out of germanium diodes | 18:57 |
bart416 | Then proceeded to use a 555 timer as audio amplifier | 18:57 |
bart416 | To finish it off with some nice LED as light sensitive receiver | 18:58 |
reportingsjr | haha | 18:58 |
reportingsjr | I wouldn't call it abuse | 18:58 |
reportingsjr | just finding different uses | 18:58 |
bart416 | lol | 18:59 |
bart416 | "tactical misplacement of components" xD | 18:59 |
lekernel | yes, but this 2N2222 probe is (a) done by an apparently very serious company (b) in a domain few electronics engineers are knowledgeable about | 18:59 |
bart416 | lekernel, we have an ancient analog circuit design professor hanging around the lab that does weird things like that... | 19:01 |
lekernel | if I asked you how to build a cheap cryogenic temperature probe, I guess you'd have a hard time figuring out "just use a 2N2222" :-) | 19:01 |
bart416 | To be honnest I'd use 4, lol | 19:01 |
reportingsjr | lekernel: I don't see why a large company would not be allowed to use a solution like this | 19:09 |
lekernel | I'm not saying it's bad or should be banned, I'm saying it's remarkable | 19:12 |
bart416 | In the end it's still an engineer designing it lekernel | 19:14 |
bart416 | And all engineers like quick, easy, reliable and cheap solutions | 19:15 |
bart416 | And if that person happens to have used a 2N2222 as temperature sensor before and he has a stack of them around when making the prototype, then why the hell not :P | 19:15 |
berndj | but why not just use a 1N400x? | 19:24 |
berndj | are they harder to find than 2N2222? | 19:24 |
bart416 | transistors are easier to use as temperature sensors | 19:24 |
berndj | and since they're using the transistor as a diode anyway... | 19:25 |
bart416 | Check the scale of influence of VT ;) | 19:25 |
bart416 | the Is of a diode and transistor are quite different | 19:27 |
berndj | hmm, you're still taking advantage of its transistorness | 19:27 |
berndj | ok never mind i said anything :) | 19:27 |
bart416 | np | 19:28 |
bart416 | Had to think about it as well for a minute, lol | 19:28 |
lekernel | nah, usually, electronics companies avoid using components for unintended purposes, because doing so tends to result in a "let's see if it works with this week's parts" kind of production | 19:36 |
bart416 | Maybe that's one of the reasons they went for the 2N2222 | 19:47 |
bart416 | It's reliably available | 19:47 |
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