Things derped engineers say. - Page 1
Forum section: electronics / general

author: joblessalex
author_rank: Contributor
timestamp: May 02, 2013, 04:35:03 am
content: In this post, I want to hear all the stupid things either you, or a friend has said about electronics. Bonus points if you can confuse the higher engineers!I'll start."it's a current limiting power supply, the circuit can't blow up!"

author: brabus
author_rank: Frequent Contributor
timestamp: May 02, 2013, 11:32:36 am
content: OK, so...A: This circuit needs 12V, 1A supply.B: nice! I can give you this 12V 3A spare supply!A:are you mad?3A would fry it!B:

author: c4757p
author_rank: Super Contributor
timestamp: May 02, 2013, 11:43:45 am
content: Quote from: joblessalex on May 02, 2013, 04:35:03 amThat's a good one. How about "It's not the voltage that kills you, it's the current"? Can't say I've heard an actual engineer ever utter that one, but a perhaps a friend...

author: Recyclojunk64
author_rank: Contributor
timestamp: May 02, 2013, 11:59:03 am
content: QuoteYeah, one of my friends has used that statement many times in conjunction withQuote

author: Rufus
author_rank: Super Contributor
timestamp: May 02, 2013, 12:06:53 pm
content: Quote from: c4757p on May 02, 2013, 11:43:45 am''volts that jolts and mills that kills'' which is quite true.

author: c4757p
author_rank: Super Contributor
timestamp: May 02, 2013, 12:25:17 pm
content: It is "true", yes, but only useful under the consideration of Ohm's law. Most of the dopes who like to recite it have no idea why a 12V 300A supply will not kill you and a 120V 300mA one will. It is both true and reckless.

author: olsenn
author_rank: Frequent Contributor
timestamp: May 02, 2013, 12:55:05 pm
content: Ohm's Law is not a law, it is a definition. The real law is P=V*I. Since either of these terms being zero would give zero power, if you have non-zero (real) power, you also have non-zero voltage and current. Dividing any two non-zero numbers will result in another non-zero number, and so we define R as that number (V/I).Back when the only electronics/circuitry was metal wires and light bulbs (no AC, semiconductors, etc) I'm sure scientists believed that voltage truly was always proportional to current (in other words it's a law) but after discovering this not to be true we just never gave up the theory because it would mean admitting we were wrong all these years... it's easier to say it is a law but has exceptions... even though laws have no exceptions.

author: c4757p
author_rank: Super Contributor
timestamp: May 02, 2013, 01:09:38 pm
content: Absolutely correct. I guess that just like I'd say "it's not the volts" is technically true but useless, I'd say considering Ohm's law there is technically false but useful. I'm really more referring to the general idea that current increases when voltage increases, regardless of the actual mathematical relationship. It's silly to say that volts don't kill, since volts make amps possible.Way too many people confuse the current that will flow through their body with the current that will flow through a metal bar. That 12V 300A supply is not 300A when you touch it, and somethingonlyhaving a lower current rating does not in any way make it safer.

author: c4757p
author_rank: Super Contributor
timestamp: May 02, 2013, 01:13:20 pm
content: Quote from: Recyclojunk64 on May 02, 2013, 11:59:03 amFor what it's worth, a car battery is incredibly dangerous. I'd rather accidentally shock myself than accidentally bridge a car battery with a wrench.

author: dr_p
author_rank: Frequent Contributor
timestamp: May 02, 2013, 01:14:37 pm
content: Me: how much cocoa does that chocolate have?Colleague (with EE degree): why does that matter?M:well, more cocoa is generally healthier.C:why?M:for starters there's less of the other stuff (sugar, colorants, flavors etc) and cocoa in itself is good for you, it's got fibers and helps some other stuff, I don't remember exactly. Ball park figure 50% cocoa is decent.C:GTFO, even the chocolate that's 75% cocoa contains all the nasty stuffM:yes, but lessC:no, they have the same amount, be sure.M:they can't have more than 25% of the other stuff, because 75% is already cocoa. DoooohC:you are implying 75% cocoa means three quarters of the chocolate is cocoa) that's insane, it's too much powderM:well, what do you thing "ingredients:cocoa(75%), ..." means?C:that the cocoa used was not pure, it was 75% pure.M:and how much of the "impure" cocoa did they use?C:I don't know..M:I do.....

author: Psi
author_rank: Super Contributor
timestamp: May 02, 2013, 01:15:57 pm
content: An engineer/lecturer at uni once told us that 'teletext' transmits your page request from your house TV aerial and the TV studio responds with the requested page.He even drew a nice diagram on the whiteboard showing the communication.The few of us in the room who knew just how wrong he was were all in shock and just let him continue.

author: c4757p
author_rank: Super Contributor
timestamp: May 02, 2013, 01:19:20 pm
content: Quote from: Psi on May 02, 2013, 01:15:57 pmYep. Can't say I haven't done that.

author: Psi
author_rank: Super Contributor
timestamp: May 02, 2013, 01:25:41 pm
content: Speaking of chocolate percentages.You should try 99% chocolate sometime, It's crazy strong.Almost impossible to chew without being overcome with bitterness. You have to let it dissolve on your tongue.http://www.lindt.com/swf/eng/products/excellence/excellence-99/

author: c4757p
author_rank: Super Contributor
timestamp: May 02, 2013, 01:30:26 pm
content: Quote from: Psi on May 02, 2013, 01:25:41 pmEw! I don't even like regular "dark" chocolate - candy should be sweet! If I want bitterness I'll drink coffee...

author: nuhamind2
author_rank: Regular Contributor
timestamp: May 02, 2013, 01:37:19 pm
content: My friend ask this in classF: Can common emitter amp be used to amplifiy electric power?Other friend in another classF:What if we couple a generator to motor and power the motor from generator?L:Power will be dissipated on the wire resistance

author: Excavatoree
author_rank: Frequent Contributor
timestamp: May 02, 2013, 01:48:29 pm
content: "That device doesn't need large wires because it draws a lot of current, the wires are large to reduce the voltage drop."

author: c4757p
author_rank: Super Contributor
timestamp: May 02, 2013, 01:49:15 pm
content: Quote from: nuhamind2 on May 02, 2013, 01:37:19 pmAs much as it shocks me every time I hear that, that's a common misunderstanding of amplifiers. I guess these people can't be bothered to think back to physics.QuoteWell... technically true...

author: Skimask
author_rank: Super Contributor
timestamp: May 02, 2013, 01:52:59 pm
content: "Hey, Watch this shit!"

author: Balaur
author_rank: Unknown
timestamp: May 02, 2013, 01:53:10 pm
content: Quote from: Psi on May 02, 2013, 01:25:41 pm</Chocolate freak/snob mode on>Eh, all this commercial stuff is rubbish (I've tasted a lot actually)Best black chocolate is made from Criollo beans. A 75% bar is sweet and almost chocolate-milk-like. A 100% bar is an acquired taste, but I definitely enjoyed very much (I'm actually in the same area as one of the last French chocolatiers who manufactures chocolate from the raw bean by himself).I do prefer milk chocolate though and my "go to" chocolate is the standard "alpine" Milka. Very good quality/price ratio.</Chocolate freak/snob mode off> Sorry

author: c4757p
author_rank: Super Contributor
timestamp: May 02, 2013, 01:57:38 pm
content: Quote from: Skimask on May 02, 2013, 01:52:59 pm

author: peter.mitchell
author_rank: Super Contributor
timestamp: May 02, 2013, 02:15:34 pm
content: Quote from: Skimask on May 02, 2013, 01:52:59 pmThat is in the same league as"How hard could it be?"and"What could possibly go wrong?"

author: ecat
author_rank: Frequent Contributor
timestamp: May 02, 2013, 02:25:55 pm
content: It must be a software problem.

author: ddavidebor
author_rank: Super Contributor
timestamp: May 02, 2013, 02:55:20 pm
content: You MUST drive led by voltage.

author: c4757p
author_rank: Super Contributor
timestamp: May 02, 2013, 03:03:10 pm
content: Quote from: ddavidebor on May 02, 2013, 02:55:20 pmI'm not even really sure what this means.

author: c4757p
author_rank: Super Contributor
timestamp: May 02, 2013, 03:07:40 pm
content: Quote from: ecat on May 02, 2013, 02:25:55 pmQ: How many programmers does it take to change a light bulb?A: None, that's a hardware problem.

author: olsenn
author_rank: Frequent Contributor
timestamp: May 02, 2013, 03:10:41 pm
content: QuoteProbably that the LED (or any diode for that matter) won't drain any current until a certain voltage threshold is reached (junction drop). Unless you plan on making use of a volatile voltage-current curve for your particular LED though, you'll need to drive the LED with a fixed current as well. Light = Power - Other Shit

author: free_electron
author_rank: Super Contributor
timestamp: May 02, 2013, 03:34:12 pm
content: Newly minted engineer (NM), straight out of uni. Masters. Analog design.Walks into my lab with 'underwhelming enthusiasm' because he is tasked with debugging an actual board as opposed to simulating it at his desk.NM walks to large cabinet with parts , opens and closes drawers , get's a more and more puzzled look on his face and lumbers over to me.NM: how can i tell for these small components (smd) what are resistors and caps. They all look the same...ME: look at the label on the bins. The capacitors have their a little omega symbol behind the value.NM: okNM rifles through cabinet and walks off with his 100kilo-pico decoupling cap.....-------PE ( paper engineer . Type that only shuffles paper around but has no practical experience. Never leaves desk ) comes to lab , has to do something on. Aboard. He is given a prototype chip and has to test power consumption on the 1.8 volt rail.He messes around for a while and cant get it to work . Calls for help.I walk over there .. One huge ball of wires going everywhere.. I trace all the wires out. His ammeter wires , through lots of bananas and grabbers were both connected to the 1.8 v rail... So in essence the ammeter is shorted and connected to 1.8 volt.I explain to him current needs to flow through the ammeter. I also explain that , in order to do that there is a nice jumper on the board that disconnects the 1.8 volt plane feeding the chip , from the regulator.PE mucks about for another half hour and calls me over. He has blown the fuses in 3 ammeters.. I look at the wiring. The ammeter is now connected from the 1v8 regulator out to .... Ground... It is supposed to be between the pins of the jumper. It aint a voltmeter ! Anyway , we were out of fuses ( and working ammeters) so i tell him : take a bench supply , set it to 1.8 volts , connect to jumper and read the current from the supply. I walk off.A few moments later i become awar of that typical smell of carbonised ic packages... Following my nose leads me to PE's bench....Sure enough. The nitwit now connected the supply between the jumper pins. So he had 1.8 being made on the board , in series with 1.8 made by the supply , thereby feeding 3.6 volts into the chip...He looks at me and say : there must be something wrong with these prototypes they all blow up at poweron...ME : how many protos do you have ?PE : 5ME : how many did you tryPE : 5ME : i guess it must be a production problem then. Its very consistent . They all blow at 3.6 volts...PE happy trundles off to write report... Not catching on to what i just said. Sure enough during slide presentation he made a nice bullet point : all chips blow at 3.6 volts.. As this is consistent it must be a fab problem....---PE2 ( a different one) is tasked to design some glue logic to match a pcmcia wifi network card( pcmcia is basically isa) onto the memory interface of a chip. We want to add wifi capabilities and use simple pcmcia cards for that purpose (2001 era. Every router was built that way then)He comes up with a circuit consisting of 11 or 12 ttl chips (74xx series). Most of em half used. Like a 7404 because he needs an inverter somewhere.... And there is an u used 7400 gate left...I go over the schematic and manage to reduce the circuitry to 5 chips.( he used 74245 as bus switch on data . I happen to know there is such thing as a 16245 for 16 bit buses.... ) no comment on that , i just happened to know that, he didn't. That was not the problem.I had minimized his pile of loose gates to two quad nand, a quad nor and a quad and. Or something like that. I had built an or gate from three nands. Simply make two inverters out of two nand gates, and slap on another nand gate.. A+B = not(notA * notB) . Simple boolean logic.He doublechecked my circuit ( as he was responsible for signoff) andexclaimed this could not work. He definitely needed an or gate for the two signals and i must have made a mistake. I tried explaining him boolean rules.. But no budging on his side. Anyway, he was going to make a quick netlist in VHDL based on my schematic and send it through the simulator....This made me print a large banner to put over his desk.. The banner said 'More TTL, Less VHDL'---Chinese collegue with -very- bad pronunciation...RING.. ( telephone). We need talk abou alice. Alice no good.? This guy has a complaint about alice ? I look around puzzled .. I don't know any alice in the department ( i had just started there like a few weeks before ) . So i ask my collegue if they know any alice .. Puzzled looks . No, we don't have anyone in the company with that name.I turn back to the phone and ask if he is sure he got the right guys ?Him : Yes yes alice wok fo poi fai.? What the hell ? Alice.. And she works for some asian sounding guy called 'poifai' .. So i turn to my collegue and say that this dude wants to talk to 'alice' who works for some guy called something that sounds like poifai.At this point the senior designer starts laughing and asks who i am talking to ... I give the name. .. He says , okay i know what this is about pass him to me. So we all look baffled .. And he explains :This chinese guy has been working on the 'Netlist' for the first chip in 0.5 micrometer technology (this was 1993...)So he found a problem in the 'netlist work for point five...'Alice wok fo poi fai.......The same chinese dude drew massive crowds whenever he gave a presentation. People went there for laughs ... One meeting he was explaining a block he designed and he kept going on about some jibberish.. Lingoselelle or something like that. The senior designers were all baffled. We were used to chinglish by now but this was a rightout brainracker... Until 5 minutes later one of the seniors , who had been diggi g in the schematics exclaimed: i know what this is. It's the ringoscillator he used here:Yes yes, lingoscelelle..Other instances : the atela... ( talking about the altera fpga on the board )

author: c4757p
author_rank: Super Contributor
timestamp: May 02, 2013, 04:06:07 pm
content: Quote from: free_electron on May 02, 2013, 03:34:12 pmWhat!? Was his master's degree printed on toilet paper or written in crayon, by any chance?QuoteI have just lost the small amount of faith in humanity I had.

author: T4P
author_rank: Super Contributor
timestamp: May 02, 2013, 05:00:54 pm
content: Quote from: c4757p on May 02, 2013, 11:43:45 amA guy on OCN claiming to be a electrical engineer kept on implying thatand said that my argument that it's actually ohms law that is the matter and he said it's still current that killsBloody idiot didn't realize my point that if he phrased it like that it will saying that a 10V source can kill you given enough currentQuote from: peter.mitchell on May 02, 2013, 02:15:34 pmJeremy clarksonQuote from: ecat on May 02, 2013, 02:25:55 pm*points to software engineer*Quote from: free_electron on May 02, 2013, 03:34:12 pmThe moments that make you goYou tell the best stories manBeing chinese myself i even found that extremely hilarious ... but yes someone with a chinese accent and doesn't have much english education will pronounce ring oscillator like thatYou know why? ringo-scilator. In chinese rin = lin ... and yes i can pull of the same accent as well but it's not i wanted much chinese education since young, nope, i didn't listen to class because i couldn't be bothered with chinese and here i am ... speaking 100% english apart from the rare times i have to communicate in chinese

author: kfitch42
author_rank: Frequent Contributor
timestamp: May 02, 2013, 05:55:14 pm
content: Quote from: c4757p on May 02, 2013, 03:07:40 pmHey! As a software guy I represent that remark!P.S. I have used the "must be a hardware problem" excuse a few too many times.

author: kfitch42
author_rank: Frequent Contributor
timestamp: May 02, 2013, 06:02:15 pm
content: Quote from: c4757p on May 02, 2013, 11:43:45 amEveryone who says that should be forced to watch this:"Its not the fall that kills you, its the landing."

author: Rufus
author_rank: Super Contributor
timestamp: May 02, 2013, 06:29:02 pm
content: Quote from: kfitch42 on May 02, 2013, 06:02:15 pmSnip stupid boring video which includes a table showing you what current (that's current not voltage) it takes to kill you.It isn't a myth he didn't bust it. It is a simple truth which needs some explaining if you are particularly dumb.

author: N2IXK
author_rank: Frequent Contributor
timestamp: May 02, 2013, 06:31:27 pm
content: Had a post-grad EE student helping out in the lab as an intern one summer. Came highly recommended, being one of the "best in his class".Anyway, we were having some issues with computers and other equipment acting up/rebooting in one part of the building, so I gave the kid a DMM, and told him to go down and check the line voltage, as the problem seemed worse on hotter days when the line voltage tends to sag. Phone rings a couple minutes later, and he proudly reports that the line voltage is 188.8 volts (this on a US standard 120V branch circuit). Because everything was pointing to a LOW voltage problem, I was a bit dubious, and asked him to recheck the reading, but he reported that the meter wouldn't turn on. When I asked him how he got the reading, he said that he put the probes into the outlet, the display flashed up "188.8", then went out.I then asked him what the knob on the meter was sent for, and he said "That little upside-down "U" thingy...". Needless to say, he didn't make it through the rest of the summer with us.....

author: T4P
author_rank: Super Contributor
timestamp: May 02, 2013, 07:59:38 pm
content: Quote from: N2IXK on May 02, 2013, 06:31:27 pmMy daily dose of fail has just arrived

author: Dataforensics
author_rank: Unknown
timestamp: May 02, 2013, 08:35:31 pm
content: Not really electronics, but I was doing a mixed engineering course around 35 years agoIn the last few weeks of the three years the whole class had to attend prize giving for the best paper on equipment used, mine did not win.The winning paper was on Milling machines, during the presentation the winner was asked to stand by one to have his photo taken. He proceeded to proudly walk up to the bank of Lathes.This probably reflects as much on his tutors!.

author: free_electron
author_rank: Super Contributor
timestamp: May 02, 2013, 09:04:20 pm
content: Quote from: N2IXK on May 02, 2013, 06:31:27 pmGive the kid some credit for checking the impedance of the grid ! After all you were after a voltage drop. Voltage drops are caused by imcreased resistance or impedance.. So he was on to something ...

author: ConnorGames
author_rank: Regular Contributor
timestamp: May 02, 2013, 09:14:10 pm
content: Quote from: free_electron on May 02, 2013, 09:04:20 pmObviously he needs to use an LCR meter. Preferably the nicest one in the lab so he can measure low impedance accurately...

author: senso
author_rank: Frequent Contributor
timestamp: May 02, 2013, 09:33:20 pm
content: I can't really understand how all those "best of the class" are of hum... DUMB!

author: free_electron
author_rank: Super Contributor
timestamp: May 02, 2013, 09:45:35 pm
content: 3 day course from cadence on some new tool. Second day halfway through the afternoon. Loud snoring from the last row ... Everyone turns around to see where it comes from ... Dr Berndsen had fallen asleep ( our swedish digital design guru).His neighbour pokes him in the ribs and Dr berndsen jolts awake and exclaims in his thick scandinavian accent. Huhuhu i fell 'asjleep'...I took 5 minutes for the laughing to stop .... The way he said that was so funny. He had this very deep voice aaand wooulld taaaalk veeryyy sloowwlee.Huuhuuhuu aiii fellll asjjleeep.---Midnight shift in the waferfab .. ( i started as a makntenance technician repairing the plasma etchers and ion implanters... )Ring. Ion implant station 3 here. The wafer handling robot is stuck.This was acommon problem. I was outside the cleanroom so i told the operator the clear the wafer basket and hit init. Meanwhile i would suit up and come in.The operator says : i don't think that will work. The endstation door is open...?? What do you mean the endstation door is open ?( for the unwashed masses. An ion implanter is a large machine. Basically an ion gun. We have long vaccuum tube ( several meters long ) with an ion gun and a mass analyzer on one end and an endstation on the other end. This endstation has a massive door that is lifted from horizontal to vertical position. In this doo there is a heavy larg rotating , watercooled, disk with clamping mechanisms. The robot takes a wafer , and loads them in the clamp. When 25 or 50 wafers are loaded in this spinning disk the door is raised vertically, the endstation is pumped vacuum , the disc is brought up to speed and the innner airlock opens. At that point the wafers are exposed to the ion beam. As the wafers spin in front of the 'business end' of the ion gun they get implanted with the dopant material. A big electromagnet deflects the beam to scan the entire surface. )So the endstation door is open... But .. The robot should be parked on the other endstation ( for throughput there are two of these endstations. The one that is 'up' and being i planted has the robot i. Front of it so it can load the one that is down.So i ask again ? Where is the robot.Sheepish answer ... Underneath the door..Me : WHAT ? Explain that again please . Where is the robot ?Operator : Underneath the door...Me : HUH ?Operator : both doors are open. The robot is underneath the left endstation...Me : ?!? What happened ?Operator : well at the end of the run there was this loud bang and the door crahshed open...It turned out one of the retaining bolts that hold the pistons that lift the door had sheared clean off. As the lock was opening the bolt gave out, the piston shot loose , ripped half the cabling out and the entire door crashed open o top of the precision wafer handleing robot. Completely crushing it i to oblivion....So we made a plaque that said : if both doors are open you got biiiig trouble..---Afternoon shift. Water alarm on implanter 4. We go and check and there is water dripping from a feedr line. We find it is the connector. So we ( my collegue and i , you always work in pairs around these implanters. They are dangerous ) apply some duct tape and call plant and facilities to replace the water feed. ( that stuff is p&f work)P&f engineer comes in and we show him where the problem is.Now this machine has a service walkway behind it that is fairly narrow. On the back wall is the mkan breaker panel for the power to the implanter. Oneof these gass assisted rotatry type breakers. Big red handle you have to grab with two hands and rotate down 45 degrees. The gas charges then shoot the switch open.( this machine draws substantial power when in operation... 380 volts at 400 ampere.. )Now, you have to know a bit about 'bunny suits'. The cleanroom overall is an annoying garment to keep skin flakes and other wate products of humins trapped inside and out of the cleanroom. It is a loose fitting garment with elasticised neck , wrist and ankle cuffs and an elesticised waistband. Basically a big garbage bag.. It always pulls and pinches i. The wrong spot if you need to kneel or bend. It is only good for walking or sitting on achair. Anything else it is annoying.So this dud pulls up the legs to remove the slack i. Order to kneel down and sit on his knees half underneath the machine and fix the leaky plumbing. As he does this he basically creates a flap of material around the waistband. Ho goes through the knees , this flap of fabric hooks the breaker arm and...You guessed it. -boom- fieuuwwwww ( sound of motors spinning down , compressed air escaping , ) kling , bang , kloink ( sound of vacuum valves popping open , breaking wafers, ion gauges popping )...This dude gets up very quickly , looks at us sheepishly and goes. 'Oh sorry'... Turns around and lifts the breaker back up.. Followed by more loud booms and bangs .....It took 3 weeks to repair the machine.... The dude was barred from ever entering the cleanroom again...---Main extraction voltage failed on one of the implanters. So the senior equipment engineer calls us 'freshman' overto show how you replace the main rectifier.The high voltage generator is a large oil filled tank that takes 380 volts and makes up to 160 kilovolts from it. Full of transformers, massive capacitors , motorized variacs and other high voltage stuff. The end rectifier is a vacuum tube... It turned out the filament had popped.So he shows us to safely shutdown the hv generator , discharge every cap usi g a special grounded stick , open the access cover , disconnect the anode wire and pull outthis vacuumtube. This thingis the size of a volleyball. Massive glass balloon rectifier.He puts a new one in . Covers everything up and goes through the startup procedure. No power.Drat.. Maybe we put it in wrong. This thing has a 4 pin base and you can put ot in wrong ...So we go through shutdown, discharge, safety yadda yadda yadaa. Pull the tube, rotate it , make sure it is i right this time and firethe machine up.The operator starts pulling beam current . At about 40 kilovolts the tube pops. Game over....So the senior engineer gets nervous. Its the end of his shift, he is in overtime, the operators are annoyed because the machine has now been down a few hours already.So he shoves us asided and decides to do it himself as he can do it faster. Rush rush rush .. And he forgets to discharge the anode..... He reaches i to the oil tank and grabs the tube.Now the bunny suits are conductive ...( not dissipative but really conductive . A few kiloohms ).This thing arcs over and hegets a massive jolt from the tube ( the suit caught most of it ,but he still got zapped good ) so he jolts up. Now. His arm was up to his elbow in this high voltage oil...Floor ,wall ,ceiling , him and me and my collegue were all drenched in oil. He had to sit down for a while because he literally say stars...

author: ddavidebor
author_rank: Super Contributor
timestamp: May 02, 2013, 09:51:56 pm
content: Quote from: senso on May 02, 2013, 09:33:20 pmschool and all-day problems are different.everyone with good memory and good brain can have 10+ at school.you only need to do thing that someone has alredy teach you, and you need to do in the same way.outside school, is the opposite.you have not pre-make answer. sometimes you don't have the question too.you need to solve problem in the best way, and is never the way someone has teach you.i see it everyday. no one that is a genius at school, is a genius outside school and vice versa.

author: lemmegraphdat
author_rank: Frequent Contributor
timestamp: May 02, 2013, 10:14:49 pm
content: Quote from: brabus on May 02, 2013, 11:32:36 amI've had like conversations with someone who will remain nameless and I don't ever want to hear this kind of $#*! ever again from this person, it creeps me out.

author: lemmegraphdat
author_rank: Frequent Contributor
timestamp: May 02, 2013, 10:47:34 pm
content: Quote from: Psi on May 02, 2013, 01:25:41 pmI wonder how it is with bacon. Gonna try that. I'll let you know.

author: c4757p
author_rank: Super Contributor
timestamp: May 02, 2013, 11:28:32 pm
content: Quote from: lemmegraphdat on May 02, 2013, 10:47:34 pmWell, it can't possibly get any worse...

author: nuhamind2
author_rank: Regular Contributor
timestamp: May 03, 2013, 12:09:22 am
content: Quote from: c4757p on May 02, 2013, 01:49:15 pmIf it is me ,I'm gonna answer "You're not thinking about free energy ,are you?"But still, I hope I never heard what my friend ask.

author: Dave
author_rank: Super Contributor
timestamp: May 03, 2013, 03:03:04 am
content: Quote from: ddavidebor on May 02, 2013, 09:51:56 pmWrong. You will see why, when you get to university.When I was still in highschool, we had a teacher that taught us practical electronics. He was a know-it-all. At least he thought he was.One day, we were messing with some opamp circuits, the teacher gave us TL072 opamps and pointed out, that those opamps were VERY rare (because he only happened to have 5 or 6 in his parts bin). My schoolmate managed to hook up the power supply in reverse (we only had red and black wires in the lab, he used red wires for both +12V and -12V line and - obviously - mixed them up) and the opamp gave up it's life with a loud pop. The teacher looked at my schoolmate with fear in his eyes and started whining that those opamps are rare and that now he won't have enough to show to other groups of students.I was just about to order some stuff from Farnell that week and asked my schoolmate if he wanted me to pick up a couple of TL072s for him give back to the teacher. I did and next week my schoolmate gave two to our teacher. The teacher took those opamps and looked at them with amazement. "But they are SO rare, where did you find them?" I spoke up: "They sell them by the thousands at Farnell." The look on his face at that point was priceless. Disappointment, surprise and annoyance, all mixed together.

author: c4757p
author_rank: Super Contributor
timestamp: May 03, 2013, 04:17:46 am
content: Quote from: Dave on May 03, 2013, 03:03:04 amI think he's saying that's what you need to do to get through school, not that that's all you need to do in school to learn properly. Think - your teacher would have been perfectly happy to pass you if you all remained complete ignoramuses with regard to the availability of TL072, right?

author: ddavidebor
author_rank: Super Contributor
timestamp: May 03, 2013, 07:38:19 am
content: Yes, but learn properly + a good education is what, 90%?...well, i've only 7/10 of average and i've ever had problem with autority of teacher.But they treat me as the best student of the school.So effectly what i've said is just for "standard" situation.

author: T4P
author_rank: Super Contributor
timestamp: May 03, 2013, 10:45:06 am
content: Indeed, so-called top students (I was nearly top but not top so i'm not in the same category) knows nothing else but the book ...He scored double distinctions but, ah f thatHe doesn't know shit about how things properly operate and thinks he's the bestWhen asked what's a quad matrix driver he has no idea(FYI our teacher covered matrix displays the other and matrix drivers but he still has no idea)After the 2nd semester my class position has fallen to the center. Lucky meNo more being the center of attention ...

author: digsys
author_rank: Unknown
timestamp: May 03, 2013, 11:04:26 am
content: Long time ago I shared a factory with a high-end medical service / supply company (once had a DNA synthesiser in for commissioning !!)One day a senior tech comes to me to ask for a fuse - give him the fuse and off he goes -5 mins later, comes back asking for another fuse - ok, give him the fuse and off he goes -5 mins later, comes back and asks for 10 fuses ! HUH? So I go back with him ... a large PILE of dead fuses on his bench?I inquire ... Wassup mate?Reply: Every time I put a fuse in, it blows.AND? Your conclusion is?Reply: Must be the fuses ! I need more ...True

author: free_electron
author_rank: Super Contributor
timestamp: May 03, 2013, 03:12:51 pm
content: I did one year of graduate course. They basically start again at zero ( ohms law) because a lot of people come in from other directions like latin-greek etc... Having had already 6 years electronics i was bored out of my skull . So i filled my time doing the seniors graduation projects, and annoying the non-teccies.We just had seen the thermal calculation. Rthjc rthca et al... Dodo number one had a power supply with a 7805 and heatsink. It kept going in thermal protection . So he came to me for advice. Always up for a bit of fun i explained that increasing the surface of the heatsink would decrease the thermal resesitance rthca. . Case being the heatsink, a being ambient. So far so good. He nodded agreeingly..But didnt have a larger heatsink. So i pulled in some other mathematics. Look at the thickness of the aluminum. If we were to drill a hole in there of the same diameter as the thickness. Lets say it is 1mm thick. The inner wall surface of that hole is thickness x diameter x pi . We only lost a bit of material in the hole ( on purpose i did not calculate what we lost , or it would have punctured the theory.. )So dodo went off drilling lots of holes in his heatsink trying to get it to work. He spent an entire lab session (4 hours) on that.

author: T4P
author_rank: Super Contributor
timestamp: May 03, 2013, 03:31:59 pm
content: Quote from: free_electron on May 03, 2013, 03:12:51 pmDodo indeed

author: c4757p
author_rank: Super Contributor
timestamp: May 03, 2013, 03:45:30 pm
content: Those are speed holes. They make it lose heat faster.

author: peterthenovice
author_rank: Regular Contributor
timestamp: May 03, 2013, 08:55:20 pm
content: dodo: Is the heat sink big enoughthe other guy: yes! but add a car water cooling system for good measuredodo:all i have is an industrial cooling systemthe other guy: that"ll do

author: staxquad
author_rank: Frequent Contributor
timestamp: May 03, 2013, 09:51:11 pm
content: Quote from: Recyclojunk64 on May 02, 2013, 11:59:03 amI always thought it was the resistance (or lack thereof) that kills you.

author: lemmegraphdat
author_rank: Frequent Contributor
timestamp: May 04, 2013, 12:28:58 am
content: Quote from: staxquad on May 03, 2013, 09:51:11 pmSquirrels and birds must have a high resistance or the induction would surely kill them.

author: Dave
author_rank: Super Contributor
timestamp: May 04, 2013, 12:42:36 am
content: Quote from: c4757p on May 03, 2013, 04:17:46 amWhat I understood is that you are shown how to solve something and you just need to be able to repeat everything to pass.So far, in my first year at the university, I've had an entirely different experience. We have been taught how to think like engineers and in order to pass the exam, you have to thoroughly understand the subject. On top of that, we are constantly encouraged to tackle more difficult tasks, which require a lot of thinking and are nothing like the tasks we encounter at lectures.

author: c4757p
author_rank: Super Contributor
timestamp: May 04, 2013, 12:45:03 am
content: I must go to a shitty school.Oh wait, I already knew that.

author: TimNJ
author_rank: Super Contributor
timestamp: May 04, 2013, 02:45:08 pm
content: Quote from: Psi on May 02, 2013, 01:25:41 pmI like dark chocolate. Milk chocolate is a little too sweet for me sometimes. 70% is good for dark chocolate new comers. I eat up to 90% now. Tried the 99% percent. Not the biggest fan.But to everyone else, dark chocolate in moderation is actually very healthy for you. My mother is a dietitian and she recommends everyone eat an ounce or two every day. Not that her word is law, but there is infact good scientific research to back that.

author: SeanB
author_rank: Super Contributor
timestamp: May 04, 2013, 03:25:22 pm
content: Havent had the 99%, but have loved the 85%. Used to buy the Cadbury's Cocoa powder in bulk 25kg bags, the lovely stuff that was so nice just in hot milk so it could dissolve.

author: peterthenovice
author_rank: Regular Contributor
timestamp: May 05, 2013, 03:10:17 am
content: Quote from: SeanB on May 04, 2013, 03:25:22 pmsounds superbly brilliant

author: free_electron
author_rank: Super Contributor
timestamp: May 05, 2013, 03:42:03 am
content: PFFF lindt ,cadbury and ghirardelli.. bunch of wannabe'sANY serious scholcolate connoseur knows the real chococlate is Belgian !Go take a look at chocolate from Callebaut. It comes with a datasheet including melting/solidifying/crystallisation points, processing temperatures for specific applications and viscosity curve. depending on the application they have different curves / mixtures. now THAT's serious chocolate. try finding one other manufacturer that specifies that.they do have a little drawback though... it's only sold in 'slabs' of 5 kilo (11 pounds ) or 10 Kg bags..http://www.callebaut.com/usen/products/chocolate/finest-belgian-dark-chocolateAlmost any chocolatier ( they guys making the fancy filled chocolates) in the world uses that as base ingredient.Chocolate is defined by LAW in belgium ! can't throw just willy nilly in there. if you start mixing animal fats or other vegetable fats it must be labeled 'fantasy chocolate' or 'product containing chocolate' . the label 'Pure chocolate' is defined by law.

author: cwalex
author_rank: Frequent Contributor
timestamp: May 05, 2013, 03:51:36 am
content: Quote from: free_electron on May 05, 2013, 03:42:03 amChocolate that comes with a datasheet. Awesome

author: ivan747
author_rank: Super Contributor
timestamp: May 05, 2013, 03:28:10 pm
content: Aaaaand the thread has been derailed...

author: Joules
author_rank: Contributor
timestamp: May 05, 2013, 08:09:15 pm
content: Too many "Do not feed the engineers" signs leads to the inevitable discussion of food and or reproduction...

author: Jimbz
author_rank: Contributor
timestamp: May 05, 2013, 10:58:45 pm
content: Quote from: joblessalex on May 02, 2013, 04:35:03 amHello, sorry to derail this thread a bit more, but what exactly is wrong with this sentence ? I am a seminoob when it comes to electronics, created an account just for this conondrum. I was always under the impression that if you limit your maximum current output via the current limiting or overcurrent protection on your PSU you can potential keep your components safe incase there happens to be a short ? If a circuit normally draws 75mA and you limit your current to 100mA would you not keep your circuit safe if there is a short ? if it exceeds the 75mA then you know for sure you have a short in your hands ? Can someone clarify this ?

author: c4757p
author_rank: Super Contributor
timestamp: May 05, 2013, 11:02:16 pm
content: Simple - if your circuit contains 10 transistors each taking 100 mA, the current limiter isn't going to prevent this from becoming one transistor taking 1A. Shorts aren't the only things that damage circuits.Obviously the numbers aren't incredibly realistic, but the point stands.

author: hammil
author_rank: Regular Contributor
timestamp: May 05, 2013, 11:22:17 pm
content: Another interpretation could be if a constant current supply was being used... The current could be set to a low value, but that doesn't stop the voltage from rocketing up due to a high-impedance load. Semiconductors can easily be blown up with even relatively low voltages if applied in the wrong way.

author: Jimbz
author_rank: Contributor
timestamp: May 06, 2013, 12:10:04 am
content: Quote from: c4757p on May 05, 2013, 11:02:16 pmI think I am missing something critical here... Why would it not limit the current ? You said that the transistors will draw 1A, fine and dandy. But why can you not limit the current to not take more than 100mA for example ? What is the point of a current limiter or overcurrent protector if it does not do that ? Isnt an OCP sort of like a reusable fuse ?Quote from: hammil on May 05, 2013, 11:22:17 pmI have no arguments here but one, arent "current limiting" and "constant current" 2 different things ? Where on one you limit the current regardless of your voltage output and the other you set the current to a value and the voltage will be drawn automatically according to your load ?

author: c4757p
author_rank: Super Contributor
timestamp: May 06, 2013, 12:12:53 am
content: Quote from: Jimbz on May 06, 2013, 12:10:04 amLook at the numbers again. If you have ten transistors taking 100mA (the correct behavior) you have 1A. If you have one transistor taking 1A you have 1A. No change in total current.

author: tom66
author_rank: Super Contributor
timestamp: May 06, 2013, 12:13:54 am
content: In addition current limiting takes some time to take effect, as the large capacitors on the power supply output may discharge into your low impedance load, damaging your semiconductor.One example: I was playing around with a 7805 and got the + and - the wrong way around. Did it once, power supply limited at 1 amp, the regulator survived. Second time, it failed short circuit between input and ground.

author: Jimbz
author_rank: Contributor
timestamp: May 06, 2013, 12:26:47 am
content: Quote from: c4757p on May 06, 2013, 12:12:53 amMy concern is not about how much they consume the current, it is more about not being able to limit the current from the power supply. If you take on of those classic 12V adapters with 500mA rated current, will it not draw a maximum of 500mA in a circuit that consumes 1A regulary, meaning your circuit likely wont work ? Is it not the same for power supply "current limit" option ?

author: IanB
author_rank: Super Contributor
timestamp: May 06, 2013, 12:32:42 am
content: Quote from: Jimbz on May 06, 2013, 12:10:04 amNot really. Both are in fact exactly the same thing.If we look at a regulated power supply, "constant voltage" and "voltage limit" are equivalent; also "constant current" and "current limit".Consider:You set your power supply to 5 V and switch it on. The power supply increases the output current until the voltage reaches a limit of 5 V and then stops. You have hit the maximum voltage threshold (possibly with no current at all if no load is connected). Whatever you do with the load the voltage will never go above 5 V (but it might go lower, for example if you short the output).Next, you set your power supply to 1 A and switch it on. Now it will increase the voltage until the current reaches 1 A and then stop. You have hit the maximum current threshold (possibly with no voltage at all if the load has zero resistance). Whatever you do with the load the current will never go above 1 A (but it might go lower, for example if you make the load a high resistance).The power supply has two limit settings: maximum voltage and maximum current. Neither one of them will exceed the limit, but at all times one or the other of them is limiting.So don't think of a "constant current supply", think of a "current limited supply". Don't think of a "constant voltage supply", think of a "voltage limited supply".If you can find a "constant voltage supply" that maintains the set voltage at its terminals when you have applied a short circuit, let me know. I'd love that supply.

author: IanB
author_rank: Super Contributor
timestamp: May 06, 2013, 12:35:50 am
content: Quote from: tom66 on May 06, 2013, 12:13:54 amAnd that depends partly on the quality of the power supply. See this thread, for instance:https://www.eevblog.com/forum/testgear/comparing-two-power-supplies/

author: Dave
author_rank: Super Contributor
timestamp: May 06, 2013, 01:04:00 am
content: Quote from: IanB on May 06, 2013, 12:32:42 amI have met one of those handsome devils that could do just that. It was 30V, 2.5kA. Yes, kiloamperes. 75kW. Kilowatts. It could maintain a constant voltage when faced with a short my sublimating the wire.This beast was in a lab I worked in last summer. It was used for testing high power DC electric motors.

author: Jimbz
author_rank: Contributor
timestamp: May 06, 2013, 01:08:27 am
content: Quote from: IanB on May 06, 2013, 12:32:42 amNow if you help me clarify one thing I may have learned something today.Let us say we want to have "constant current" of 100mA on a random load, and it will set its voltage to 25V, the voltage will not drop or go above it, all it wants is to maintain its 100mA. And now let us set a "current limit" to 100mA, am i to understand correctly, that it will not go above 25V on the same load ? Regardless what it says on the display screen ? Also am I correct to understand that you can fiddle with the voltage as much as you want, you can always go below in "current limit" but never above with voltage with the same load ? If you go below 25V you drop your 100mA to a lesser value, does this not differentiate "constant current" and "current limit" ? In where one you have set voltage and set current on a load, but in the other you can play around with the voltage as much as you want, but the voltage will never go above the current limit of 25V ?Also could you please clarify for me why would the voltage increase in a short circuit ? I was always under the impression the only the current will increase ?Sorry if I may seem like a dunce, but I was always under the impression that the voltage and the resistance determine the current, but from what I understand from your text its the current that determines the voltage.

author: tom66
author_rank: Super Contributor
timestamp: May 06, 2013, 01:10:11 am
content: I have two 12V, 98A power supply for server use. A 20cm length of AWG26 was melted on the output and the voltage didn't drop by more than 0.1V. The wire glowed white hot before failing and now my room smells of melted rubber.

author: c4757p
author_rank: Super Contributor
timestamp: May 06, 2013, 01:15:14 am
content: The voltage output will never go above the set voltage in a decent power supply, but it will go below to restrict the current.Quote from: Jimbz on May 06, 2013, 01:08:27 amBasic algebra. Any equation can be reversed. If 2V gives you 2A, then 2A gives you 2V.

author: Jimbz
author_rank: Contributor
timestamp: May 06, 2013, 01:51:30 am
content: Quote from: c4757p on May 06, 2013, 01:15:14 amYes I realize that, but this does not really have anything to do with the matter at hand. Also in your previos post, what does the maximum of the current and the maximum voltage have anything to do with limiting said parameters ? If my power supply can go upto 50 volts and 10 amps, then why do these matter at all when i limit the votlage and current at lesser values. In constant voltage mode, it will draw its own current, but not above the maximum 10A, in constant current mode it will draw its own voltage, but not above the maximum 50 volts. I can limit the voltage and current in lesser values as I please, all dependant on the load.Main argument was that "constant current" and "current limit" are not the same... In my eyes, they arent the same, how can they be, in one mode you will always have a constant current and voltage at the same time, depending on the load. In the other, you will have your current maximum value set to a point, you can fiddle around with the voltage, but it will never go over your set limit, only under ?I do not have a bench power supply myself, but this is as much as I have gathered from the videos and tutorials over the internet

author: c4757p
author_rank: Super Contributor
timestamp: May 06, 2013, 01:59:26 am
content: Quote from: Jimbz on May 06, 2013, 01:51:30 amWhen did I say that?QuoteA constant current and voltage at the same time? What if I set a constant 1V, 1A and connect a 2 ohm resistor across the output? The only way it can get 1A is to output 2V and the only way to get 1V is to output 0.5A.They are the same thing being used in different ways. A "current limited" supply is typically being used under its set current, and a "constant current" supply is typically being usedatits set current.

author: Jimbz
author_rank: Contributor
timestamp: May 06, 2013, 02:15:24 am
content: Quote from: c4757p on May 06, 2013, 01:59:26 amWhen did you say that ? Well... you didnt, got the guys forumgoers mixed up in page 5 xD I just looked at the flag, not the username, and hastily responded...Dunno about you, but I have never in my life seen a power supply that allows you to have CC and CV on at the same time. You enable one and the other disables, also come to think of it, I think this post was not ment for you, lolz

author: c4757p
author_rank: Super Contributor
timestamp: May 06, 2013, 02:36:00 am
content: Understood.Quote from: Jimbz on May 06, 2013, 02:15:24 amI have yet to see one whereyouenable one. Typically there is a set voltage and a set current, and it just tries to deliver the maximum of both without exceeding either.

author: lemmegraphdat
author_rank: Frequent Contributor
timestamp: May 06, 2013, 03:37:46 am
content: Quote from: c4757p on May 06, 2013, 01:15:14 amYes, because on the right side of the equation it is saying that a resistance changes a current into a voltage. On the left side is it better to say that a conductance gives a current?

author: c4757p
author_rank: Super Contributor
timestamp: May 06, 2013, 03:51:59 am
content: If you like to think of it that way, I'd say so. Additional resistance requires additional voltage to push current (V = IR), and additional conductance permits additional current when given voltage (I = VG). (G is conductance.)However - I do think conductance is a good thing to understand for your own personal electrical intuition (I tend to picture resistors as restricted conductors, for instance), but using two different names for what is essentially the same thing adds confusion to most discussions. I think it's to be avoided when giving explanations, even if it's personally useful to you.

author: lemmegraphdat
author_rank: Frequent Contributor
timestamp: May 06, 2013, 03:52:46 am
content: Quote from: c4757p on May 02, 2013, 11:28:32 pm99% was sold out. Tried bacon with 85%. Flavors cancelled out. Just a greasy texture.

author: lemmegraphdat
author_rank: Frequent Contributor
timestamp: May 06, 2013, 04:05:11 am
content: Quote from: c4757p on May 06, 2013, 03:51:59 amWhen I get confused I get pissed off and that's how I know I'm learning something new or a different way to look at something old. And then it is fun to combine things, like the above. Especially when I'm half asleep, like now. I'll have cool dreams somrtimes

author: IanB
author_rank: Super Contributor
timestamp: May 06, 2013, 04:28:11 am
content: Quote from: Jimbz on May 06, 2013, 01:08:27 amLet's make this concrete with an actual example. Let our "random load" be a 10 ohm resistor.We have set our power supply to have a current limit of 100 mA and a voltage limit of 25 V. What's going to happen?Well the power supply is going to vary the output voltage until a current of 100 mA is flowing through the load resistor. When this happens the output voltage will settle at 1 V (10 ohms x 0.1 A = 1 V). Since 1 V is lower than the voltage limit of 25 V the power supply can do this and all is good.Now suppose we replace the load with a 1000 ohm resistor. The same thing will happen; the power supply will vary the output voltage until the current through the resistor is 100 mA. With our 1000 ohm resistor the required voltage will be 100 V. The power supply will keep increasing the voltage towards 100 V, but before it gets there it will hit the voltage limit of 25 V. When this happens the voltage may not go any higher, so the supply will switch to voltage regulating mode and try to keep the voltage at 25 V instead. The system will settle with a voltage of 25 V and a current through the load of 25/1000 = 0.025 A or 25 mA.As you can see, the power supply is not "constant current", because the current varied between 100 mA and 25 mA in the two cases. Also the power supply is not "constant voltage" because the output voltage varied between 1 V and 25 V in the two cases.QuoteI don't see where I said that, but I have edited my original post for increased clarity.

author: blasto9000
author_rank: Contributor
timestamp: May 06, 2013, 09:30:29 pm
content: Quote from: Psi on May 02, 2013, 01:25:41 pmActually, I rather enjoy the "strong" Lindt chocolate so long as there's enough peanut butter handy.(BTW, I've been to many countries and everyone I've ever mentioned that to thought it was disgusting. So ifyou're gagging right now at the thought of chocolate + peanut butter, I won't take it personally.)

author: c4757p
author_rank: Super Contributor
timestamp: May 06, 2013, 09:44:38 pm
content: Quote from: blasto9000 on May 06, 2013, 09:30:29 pmReally? It never occurred to me that people would think that's a weird combination.

author: IanB
author_rank: Super Contributor
timestamp: May 06, 2013, 09:49:02 pm
content: Quote from: c4757p on May 06, 2013, 09:44:38 pmYeah, peanut butter and chocolate is pretty much an American cultural phenomenon, one heavily promoted by Reese's.

author: ddavidebor
author_rank: Super Contributor
timestamp: May 06, 2013, 09:50:40 pm
content: Yeeah every places has it.In italy we have nutella!

author: c4757p
author_rank: Super Contributor
timestamp: May 06, 2013, 09:51:31 pm
content: But they're sogoodtogether!!Quote from: ddavidebor on May 06, 2013, 09:50:40 pmThat stuff is motherf-ing delicious too.

author: ivan747
author_rank: Super Contributor
timestamp: May 06, 2013, 11:32:17 pm
content: This is going to be nominated for EEVBlog's derailed topics 2013Back in derailed topics 2012 the thread got itself derailed...https://www.eevblog.com/forum/chat/best-hijack-of-an-eevblog-topic-for-2012/And by the way, I haven't got a chance to try nutella.

author: lemmegraphdat
author_rank: Frequent Contributor
timestamp: May 07, 2013, 01:56:23 am
content: Quote from: ddavidebor on May 06, 2013, 09:50:40 pmYou also have cannoli. I love cannoli. We got a real italian makes it good. And the pizza, oh man.

author: smashedProton
author_rank: Frequent Contributor
timestamp: May 07, 2013, 02:00:55 am
content: Today my chemistry teacher completely butchered electronics when teaching the electrochemistry unit.In one 40 min period, he: neglected to mention ohms law, declared the mains to be dc, ridiculed electricians as being dumb asses when posting "danger high voltage" signs, and claimed that a car battery can kill. A real nutjob...

author: c4757p
author_rank: Super Contributor
timestamp: May 07, 2013, 02:01:13 am
content: Quote from: ivan747 on May 06, 2013, 11:32:17 pmNo, it's only slightly changed. We've gone from talking about things said by derpy engineers to being engineers saying derpy things. I for one say that's on topic.

author: c4757p
author_rank: Super Contributor
timestamp: May 07, 2013, 02:02:14 am
content: Quote from: smashedProton on May 07, 2013, 02:00:55 amDude, shut up about our schools! You'll make them all think we're stupid...

author: N2IXK
author_rank: Frequent Contributor
timestamp: May 07, 2013, 02:09:36 am
content: A car battery could certainly kill you. Just have one blow up in your face, or drop onto your head from a sufficient height...

author: digsys
author_rank: Unknown
timestamp: May 07, 2013, 04:21:22 am
content: ... speaking of which, does anyone know how to sew silk onto denim? Would I need a cross-stitch?

author: smashedProton
author_rank: Frequent Contributor
timestamp: May 07, 2013, 05:05:17 am
content: Quote from: c4757p on May 07, 2013, 02:02:14 amI just realized that it has been a common topic for me to dislike my school... Thank you. I shot him an email; he didnt realize that he implied that.It just aggravates me when professional teachers (payed 80 grand a year in this case) don't bother to fact check.

author: Skimask
author_rank: Super Contributor
timestamp: May 07, 2013, 07:06:08 am
content: Quote from: smashedProton on May 07, 2013, 05:05:17 amI used to think, rather used to want to believe, that "professional teachers" would deliberately feed students misinformation with the intent to "get caught" to see if anybody was paying attention and would call them out on it.Ya, not so much...For the most part, they believe what they want to believe, and nobody can change that, sometimes even after presented with hard evidence to the contrary.

author: grumpydoc
author_rank: Super Contributor
timestamp: May 07, 2013, 09:03:46 am
content: QuoteOh <Deity>, yes! Especially with peanut butter.Just don't look at the ingredients list!!

author: free_electron
author_rank: Super Contributor
timestamp: May 07, 2013, 03:11:24 pm
content: Quote from: IanB on May 06, 2013, 12:32:42 amHold it ! .. rewind ....they are NOT the same.A curent limiting supply monitors the current it delivers. if you go over a preset limit the output turns off ( voltage goes to 0 , no more output) intil you reset the supply and turn the output back on. certian agilent( HP) supplies have such a mode. basically acts like a circuit breaker. go over the limit and we cut you offconstant current: if you hit the limit the supply modulates the output voltage so you don't go over that limit. if you hit the 2 ampere it will strt lowering the output voltage so you don't go over 2 ampere.

author: free_electron
author_rank: Super Contributor
timestamp: May 07, 2013, 03:17:28 pm
content: Quote from: smashedProton on May 07, 2013, 02:00:55 amlaws.. who need's em. take a tunnel diode for example.. f*#$ ohm's law ...for very short time intervals the mains can be considered DC yes ...high voltage is not dangerous. jus't don't create a pathway to make the electrons flow...a carr battery can kill. short a fully charged one with a big sturdy wrench and it may fling boiling sulphuric acied and lumps of lead your way potentially killing you. also if it were to be dropped of a 3 level building on your head it will kill you.on the other hand. chemistry teachers knwo all about blowing themseves up , or otherwise poisoning themselves and their environment. maybe your teachers brain has been 'pickled' by snorting whatever vapors are produced in his lab...

author: c4757p
author_rank: Super Contributor
timestamp: May 07, 2013, 03:18:43 pm
content: Quote from: grumpydoc on May 07, 2013, 09:03:46 amI'm American - ingredients lists don't scare me.

author: c4757p
author_rank: Super Contributor
timestamp: May 07, 2013, 03:25:57 pm
content: Quote from: free_electron on May 07, 2013, 03:17:28 pmAgreed. Especially in electrochemistryI think it's more important to look at the real underlying physics, not just the simplified version. Ohm's law only applies to classical conductors. Part of me suspects that even copper probably could have extremely small semiconductor effects due to impurities. Chemistry is not the place to neglect the "what ifs".That said, Ohm's law is nice for safety purposes, simplified to "increased voltage usually gives increased current".QuoteSure. And for very small spatial sections I can be considered massless.QuoteCar batteries scare the piss out of me. Working around that is like having a little bomb in front of me. I'll take HV any day, TYVM.

author: SeanB
author_rank: Super Contributor
timestamp: May 07, 2013, 05:45:14 pm
content: Car batteries are not a problem, they do have internal resistance. Now take a wet cell NiCd cell, internal resistance tends to approach zero, for almost all currents and at almost any state of charge. Now add to this the demand of a jet starter motor/generator, which can both source and sink 8kA for around a minute without failure, and consider that the charge circuit is not temperature compensated, and the battery does have a negative temperature coefficient. That is why jet aircraft have a single very strict limitation of no more than 2 start attempts before removing battery and replacing, they do tend to go thermonuclear. Not good when you are sitting on top of it, and right next to it is a evaporating coil for the airconditioning, fed conveniently with LOX from the cryotank next to it, and used to give the pilot both oxygen and pressurise his g suit.

author: c4757p
author_rank: Super Contributor
timestamp: May 07, 2013, 05:47:29 pm
content: Yeah, I'd say that's just a bit more dangerous than a car battery.Still don't like the damn things, though...

author: SeanB
author_rank: Super Contributor
timestamp: May 07, 2013, 06:06:09 pm
content: Yes, but the pilot got out of the plane ( with an armed ejection seat), opened the hatch and removed the battery and threw it away from the plane. Impressive when you consider the battery is held in the mounting with a M6 bolt, which is locked with a wire locking so it does not come undone. He had no tools other than Adrenaline. Needed a new frame and battery to fix that one, both were broken, one was very well cooked.Only thing I did was jump start helicopters. Battery switch left on, so flat battery in the morning ( security wanted a radio to listen to FM, which aircraft AM radios can do to some degree) so next morning I brought up tthe DC plant and gave a quick 5 minute lesson to the pilots on the required procedure in case the battery got very unhappy, and had 3 big fire extinguishers nearby just in case. 20 minute later they left safely with a cool battery.

author: smashedProton
author_rank: Frequent Contributor
timestamp: May 07, 2013, 09:17:42 pm
content: I wasnt clear enough. He said that a 12 volt battery would push 600 amps through your heart. He never mentioned the chemical danger

author: c4757p
author_rank: Super Contributor
timestamp: May 07, 2013, 09:19:56 pm
content: I figured that, we're just having some funderailingenhancingthe thread.(How did he get his job, exactly?)

author: smashedProton
author_rank: Frequent Contributor
timestamp: May 07, 2013, 09:34:46 pm
content: I'm afraid to ask.Like always, google saves the day:http://data.kitsapsun.com/wa-school-staff/324166H#axzz2Se38JkqC

author: ivan747
author_rank: Super Contributor
timestamp: May 07, 2013, 09:37:13 pm
content: So, he earns 80 grand a year... What should I do with my life now

author: smashedProton
author_rank: Frequent Contributor
timestamp: May 07, 2013, 09:41:13 pm
content: Its common for teachers to get a pay raise in the order of 5 grand by hosting a club. He hosts science club. That, combined with the head of the science department, tenure, and a safe track record raise his salary. It doesnt seem honest. That's the same as my dad. He is a senior engineer...

author: c4757p
author_rank: Super Contributor
timestamp: May 07, 2013, 09:46:23 pm
content: Does he whine about his salary like every high school teacher I've ever had? (Mine made about that much too, and I live in an area where the cost of living is incredibly low...)They like to whine about time spent grading, too. Dude, that was myjoblast year. I did more papers than them in half the time and didn't bitch once, and that was diff eq...

author: lemmegraphdat
author_rank: Frequent Contributor
timestamp: May 07, 2013, 10:27:38 pm
content: Quote from: c4757p on May 07, 2013, 09:46:23 pmThese folks knew what the pay was gonna be. They took the job. What they are is a bunch of trouble makers.

author: prazzb
author_rank: Newbie
timestamp: May 08, 2013, 06:43:35 pm
content: When i was in college, a gal came in late to join academics. So the professor made me explain all the previous practicals.Colleges start from basics, so I was explaining a non-inverting op-amp circuit. After my complete explanation,Q: Do all these grounds need to be connected together on the breadboard ?Me:

author: free_electron
author_rank: Super Contributor
timestamp: May 08, 2013, 07:43:35 pm
content: Quote from: prazzb on May 08, 2013, 06:43:35 pmmy answer. no , they could also be connected together elsewhere ....

author: tom66
author_rank: Super Contributor
timestamp: May 08, 2013, 11:07:17 pm
content: Isn't it more fun to have grounds at multiple potentials?

author: Flávio V
author_rank: Regular Contributor
timestamp: May 09, 2013, 08:37:24 pm
content: Quote from: tom66 on May 08, 2013, 11:07:17 pmIt is even more fun if the Gnd is at a higher potential than the input voltage(Vcc)...

author: tom66
author_rank: Super Contributor
timestamp: May 09, 2013, 09:20:45 pm
content: Or if it's at 50 or 60Hz!

author: smashedProton
author_rank: Frequent Contributor
timestamp: May 09, 2013, 09:35:45 pm
content: I once drew one amp from a smps between the 5 and 12 amp rails to get 7 volts 70 watts. I won't do thaf again..I leatned that my smps had its protection on the ground path

author: c4757p
author_rank: Super Contributor
timestamp: May 09, 2013, 09:42:14 pm
content: And it's not designed to sink current on the 5 volt rail.

author: ConnorGames
author_rank: Regular Contributor
timestamp: May 10, 2013, 12:59:52 am
content: I learned what happens when the output ground from a power adaptor for a RepRap becomes disconnected while the center positive pin remains connected... The ground current (~3A) all flows into the USB port of the connected PC. This results in a drop nearly equal to the Vgs(th) of the external mosfet it is controlling(properly grounded), causing it to operate in linear mode. The mosfet also starts to have a mind of its own because the stepper motors turn on and off, changing the voltage drop across USB ground. Wont do that again. Amazingly, nothing blew in the ~30 seconds it took me to realize I had a problem, but the unheatsinked D2PACK FET, which was supposed to be switching 24v at ~4 amps did get QUITE hot!Grounding problems are just SO FUN! Don't you agree!

author: c4757p
author_rank: Super Contributor
timestamp: May 10, 2013, 01:41:17 am
content: Quote from: ConnorGames on May 10, 2013, 12:59:52 amA power adapter like that shouldnotbe earth ground-referenced. This is why.

author: ConnorGames
author_rank: Regular Contributor
timestamp: May 10, 2013, 04:24:33 pm
content: Quote from: c4757p on May 10, 2013, 01:41:17 amOriginally, it wasn't earth grounded, but I had made a separate connection to the output ground to get it at the same potential as the external PSU for HBP, an ATX supply with a boost converter attached. Without that the MOSFET tended to be... Unhappy. And I was not about to spend the extra money for an isolated 24v supply that can put out 4 amps!Maybe a resistor between the two grounds would be a good idea. (The only current that SHOULD be flowing between them is the MOSFET gate drive)Never mind. I connected the ground wire "properly" now, to the main pcb instead of the outside of the barrel jack connecter. This horrible clip wire connection was what allowed the grounding issue, it would need a picture to explain.

author: c4757p
author_rank: Super Contributor
timestamp: May 10, 2013, 05:12:42 pm
content: I suspect something is wrong. That doesn't sound... possible.

author: Rick Law
author_rank: Super Contributor
timestamp: May 11, 2013, 01:47:32 am
content: I am no engineer and I’ve never said this, but at times, I've seen someone who thinks this:I think all my employees are like OpAmps, but I prefer to treat them like fuses.What do you mean?Well,First, instead of resolving differences with the next guy, each amplifies the difference with the guy next to him. Any small difference becomes as large a differences as they can make it;Second, they seem to work better with negative feedback;Third, when given just negative feedback, they are all good followers.And lastly, none of them are ideal;But what is this fuse thing?Well, you pick out one that can do the job, let him work till he is burned out; then go get another one just like him and start over.Ah, funny Op Amps should work for a vacuum tube...What?First, you are an empty shell;Second, you are full of hot air;Third, you do way too little for your size;Fourth, you are too power hungry.

author: poorchava
author_rank: Super Contributor
timestamp: May 11, 2013, 07:44:28 am
content: I have proven that probe shield and chassis in a cheap Atten scope can withstand shorting the secondary of 500VA, 12V mains transformer. You know... the ground....