Virgin Physicists
from InternetCitizen2@lemmy.world to science_memes@mander.xyz on 02 Jul 15:22
https://lemmy.world/post/32367614

cross-posted from: lemmy.world/post/27589038

#science_memes

threaded - newest

ArcaneGadget@lemmy.world on 02 Jul 15:33 next collapse

Welcome to the field of engineering! Your first lesson will be; “Tolerances and you”!

lnxtx@feddit.nl on 02 Jul 16:02 next collapse

+/-15 %? Good enough!

rikudou@lemmings.world on 02 Jul 16:07 next collapse

If it fits, great! If it doesn’t, you didn’t use enough tape.

Fillicia@sh.itjust.works on 02 Jul 22:16 collapse

A failed inspection is just an invitation to use a different method until it passes.

TheTurner@lemmy.zip on 03 Jul 04:39 next collapse

As a calibration technician, this makes me hurt. Lol.

Spacehooks@reddthat.com on 03 Jul 07:20 next collapse

Cringes in Monte Carlo.

squaresinger@lemmy.world on 03 Jul 08:26 collapse

pi == 3

nomecks@lemmy.wtf on 02 Jul 16:09 next collapse

Pi is roughly 5.

I_Has_A_Hat@lemmy.world on 02 Jul 16:28 collapse

Never, in any engineering field, have I EVER seen anyone simplify pi to 5. For that matter, I have never seen anyone simplify to 3. It is always 3.14. I feel like pi simplification is a weird meme that people think engineers do but is never practiced anywhere.

It’s like if there was a meme about chefs saying they always replace eggs with grapefruit. No they don’t, and it’s nonsense to think they do.

bus_factor@lemmy.world on 02 Jul 16:58 next collapse

There’s less and less reason to do it (and it’s never 5). On systems without floating point you might want to round it a bit, but only if the specific thing you’re doing allows it, and even then you’re more likely to do a fixed-point approach by using e.g. 314 and dividing by 100 later, or adjusting that value a bit so you can divide by 128 via bitshift if you’re on a chip where division is expensive. However, in 2025 you almost certainly should have picked a chip with an FPU if you’re doing trigonometry.

And while rounding pi to 3 or 4 is certainly just a meme, there are other approximations which are used, like small-angle approximations, where things like sin(x) can be simplified to just x for a sufficiently small x.

Kaboom@reddthat.com on 02 Jul 18:01 next collapse

There’s a lot of weird stereotypes out there that make no sense. Like the whole “programmers wear thigh high socks” thing. Where did that even come from?

BananaIsABerry@lemmy.zip on 02 Jul 19:50 collapse

Bet that one was started by all those dastardly programmers that wear knee high socks!

qjkxbmwvz@startrek.website on 02 Jul 18:10 next collapse

For back-of-the-envelope or mental calculations, pi is often 3 or 10^(1/2).

The latter is better than 1% accurate, and has nice properties when doing order-of-magnitude/log space calculations in base 10.

mrgoosmoos@lemmy.ca on 02 Jul 19:50 collapse

you’ve never seen anybody simplify it to 3 when doing head calcs without a phone nearby?

it doesn’t happen often, in fact I’ve seen it once. in a decade.

I_Has_A_Hat@lemmy.world on 02 Jul 21:30 collapse

The only time you should be doing head calcs as an engineer is to double check that you have a reasonable answer with the actual calcs on your actual calculator.

GreatAlbatross@feddit.uk on 02 Jul 17:11 collapse

Second lesson: Pi is around 3.

barbedbeard@lemmy.ml on 02 Jul 15:39 next collapse

Where are the spherical cows?

Num10ck@lemmy.world on 02 Jul 15:58 next collapse

would be a great band name

CaptainBlagbird@lemmy.world on 02 Jul 17:40 collapse

No no no no, I think you got that wrong. Chickens are spherical, cows on the other hand are cuboid. And humans are cylindrical.

MyFriendGodzilla@lemmy.world on 02 Jul 18:50 next collapse

Chickens, cows, and humans all are toroids. True story.

faythofdragons@slrpnk.net on 02 Jul 19:25 collapse

Can confirm, am shaped like a weird donut

Test_Tickles@lemmy.world on 02 Jul 19:35 collapse

You do have 2 holes on either side that meet the middle and are continuous from 1 end to the other. So yeah, you are the weirdest of donuts.

svcg@lemmy.blahaj.zone on 02 Jul 22:41 collapse
Venus_Ziegenfalle@piefed.social on 02 Jul 15:39 next collapse

The humble potentiometer:

ChaoticNeutralCzech@feddit.org on 03 Jul 06:27 collapse

The least reliable resistor. Not to mention the trial-and-error getting it close enough to the target value.

Spacehooks@reddthat.com on 03 Jul 07:24 collapse

linear potentiometer 100% pain, but Multi meter and rotary or digital potentiometer could be simple enough.

ChaoticNeutralCzech@feddit.org on 03 Jul 07:35 collapse

Nope, same problem as linear. Can you get angle correct to 4 decimal places and prevent the contact from oxidation?

“Digital potentiometers” are rotary encoders, which are switches, not resistive dividers. They are a useful input device for a microcontroller but not in an analog circuit.

Another option is a multi-pole rotary switch with selectable resistors in each position, but that only gives you the available values.

They are all larger and more expensive. Just use two E12 resistors in parallel or series, you can always get within 1 %. They cost a dime a dozen. The series was made for such combinations – did you know that 180 Ω and 220 Ω in parallel gives 99 Ω, a value useful for 1/100 dividers?

Spacehooks@reddthat.com on 03 Jul 08:18 collapse

Good info. Cheers mate!

Haus@kbin.earth on 02 Jul 15:48 next collapse

Use 2 E192 in parallel: a 6.19Ω resistor with a 4500Ω resistor. This gives 6.1846Ω which is close enough for rock and roll.

Lemminary@lemmy.world on 02 Jul 16:19 next collapse

I feel like this is one of those comments I want to hoard in the off chance that I ever get into this and start building shit but I know deep inside me that’s never gonna happen.

deranger@sh.itjust.works on 02 Jul 16:49 next collapse

Just learn the math, it’s quite easy. IIRC you just add the reciprocals of the resistors then take the reciprocal of the answer.

1/Req = 1/R1 + 1/R2 + 1/R3 ….

[deleted] on 02 Jul 17:00 next collapse

.

Lemminary@lemmy.world on 02 Jul 17:13 next collapse

Ohh, I remember this from uni physics class. I guess I just don’t know how to apply it in any practical sense though. Lol Thanks for reminding me!

ggtdbz@lemmy.dbzer0.com on 02 Jul 20:33 collapse

The standard resistor values are a bit weird at first but when you’re in the zone and you start getting used to what they usually are you start becoming relatively decent at making an educated guess for what the values should be. The actual IRL values are predictably defined and you start remembering the possible options over time.

Someone’s probably made a program that can do it for you though. My own shitty circuits are all built from standard example circuits so I haven’t had to think about this stuff often. Or like I’ll mix and match them illogically in a pinch (on the breadboard) and figure it out later (I don’t build the final circuit lol). Or of course, the venerable using-a-potentiometer-exactly-where-you-shouldn’t technique, which is one of the pillars of modern engineering.

Lemminary@lemmy.world on 02 Jul 20:54 collapse

you start becoming relatively decent at making an educated guess

Oh, this reminds me of a guy who could guess hexadecimal colors by eye after doing it for a while, and also another guy who could guess some concentrations in a test tube without using the spectrometer. Kinda wild but it makes sense.

anguo@piefed.ca on 03 Jul 01:23 collapse

He probably played a lot of hexcodle.

Denvil@lemmy.ml on 02 Jul 19:49 collapse

Note that if it’s a series circuit you simply add resistance.

I’m just an electrician though, we don’t actually use the math or the theoretical stuff terribly often

marcos@lemmy.world on 02 Jul 18:03 collapse

For you and anybody else wondering, the GP is a joke and should not be taken seriously.

The reason there isn’t a resistor with the value on the meme is because real resistors have error tolerances and are never the exact value on their marks. If you go assembling a card-castle of resistors with the wrong value so that the labels add up to the value you want, you will still have a resistor of the wrong value.

xthexder@l.sw0.com on 02 Jul 19:11 next collapse

The actual method for calibrating exact resistor values involves starting with a lower resistance and etching away parts of it with a laser to get to the exact value you want. You probably still couldn’t get as many decimal places as OP tho

trolololol@lemmy.world on 02 Jul 20:17 collapse

And then in a week it drifts into a different value and you have to calibrate it again.

And that’s assuming your room temperature is controlled for all experiments.

And that’s also assuming the current going through it is 0 so it is always exactly at room temperature.

Virgin theoretical physicist vs Chad experimental physicist goes brrr

sepi@piefed.social on 02 Jul 20:40 next collapse

As a layperson, what happens if crumbs from my sandwich fall all over your chad experiment setup?

xthexder@l.sw0.com on 02 Jul 20:42 collapse

For really sensitive applications like voltage references, they actually build a little enclosure around the part with a built in heater to keep it at a constant calibrated temperature. The boards also often have cutouts to reduce thermal transfer and things like the board flexing causing stress to the part.

The resistor itself won’t really drift at a constant temperature, especially in a sealed environment where condensation, corrosion, and dust aren’t a factor.

dangercake@feddit.uk on 02 Jul 21:42 collapse

Though of course real programmers use vim

Fillicia@sh.itjust.works on 02 Jul 22:14 collapse

Emacs or die

martinb@lemmy.sdf.org on 03 Jul 05:45 collapse

Emacs means die. Vim4lyfe

anomnom@sh.itjust.works on 03 Jul 09:02 collapse

I just raw dog it in Pico most of the time.

martinb@lemmy.sdf.org on 03 Jul 11:39 collapse

How?? Muscle memory fails me every time

anomnom@sh.itjust.works on 03 Jul 13:56 collapse

I only ever used it in command lines. And use other simple IDEs (Textmate and a bunch of custom bundles on a Mac…) occasionally Atom based IDEs for some embedded electronics too, but only really as a hobby.

captainlezbian@lemmy.world on 03 Jul 05:41 collapse

There’s an old saying that engineers measure with a micrometer, mark with a grease pen, and cut with a hatchet. You do the math right first, check the tolerances and tools at hand, then you try whatever seems like it’ll work keeping room for your second and third guesses. Never give the boss their company credit card back until you’re pretty sure you won’t need another hardware run of the day.

marcos@lemmy.world on 03 Jul 16:59 collapse

Still, it’s useless to try to get a board of the right size by nailing together boards you’ve cut wrong. You throw it out and try to make a better cut on the next one.

InternetCitizen2@lemmy.world on 02 Jul 17:28 next collapse

This guy electrons!!! <3

ChaoticNeutralCzech@feddit.org on 03 Jul 06:20 collapse

E192 resistors are expensive. E6 resistors 6.8Ω and 68Ω in parallel, available pretty much everywhere components are sold, result in 6.1818 Ω, which is within 0.05 % of the target, around the edge of what you can achieve without active temperature compensation.

21Cabbage@lemmynsfw.com on 02 Jul 19:49 next collapse

I kinda wonder if there’s a specific reason for that number other than just being an ass.

DragonTypeWyvern@midwest.social on 02 Jul 20:11 collapse

2pi

a_wild_mimic_appears@lemmy.dbzer0.com on 02 Jul 20:30 next collapse

would start with 6.28

DragonTypeWyvern@midwest.social on 02 Jul 21:23 collapse

He’s bad at math/estimating

Siethron@lemmy.world on 02 Jul 20:44 collapse

Tau

pigup@lemmy.world on 02 Jul 23:23 collapse

wau

bennieandthez@lemmygrad.ml on 02 Jul 20:45 next collapse

just get a variable resistance, aka a potentiometer, and have fun adjusting it to get that value.

captain_aggravated@sh.itjust.works on 03 Jul 08:15 next collapse

You’re getting a 10 ohm resistor and liking it.

Aceticon@lemmy.dbzer0.com on 03 Jul 10:48 collapse

More seriously, if you order it from an Electronics supplier, you can get a 6.2 Ohm resistor with a mere 1% tolerance (in some cases, even 0.5%).

That said an EE, except in very specific cases such as reference resistors, would generally use a 10 or 5 Ohm one with 10% tolerance for any circuit that was supposed to be mass produced since it’s far cheaper and much more easy to source in the size you require.

captain_aggravated@sh.itjust.works on 03 Jul 12:34 collapse

Electronics engineering is a bit beyond my scope; as an electronics hobbyist or field repairman you’re gonna get the closest I have in my kit at the time, I’ll probably get within an order of magnitude of the spec unless it’s somehow very damn critical or the schematic calls for one of the oddly common oddly specific values like 220 ohm.

Aceticon@lemmy.dbzer0.com on 03 Jul 12:42 collapse

Well, just think “How would I do this cheaply and get away with it” for a good enough “Engineering” approach for this case.

The really expert “Engineering” stuff related to things like maintenability, reliability, robustness and so on (which I myself am not qualified to talk about, as even though I have an EE degree, that’s not actually the domain of Engineering I ended up working in so I haven’t accumulated the professional experience that teaches one to take such higher level considerations into one’s designs), isn’t, IMHO, really necessary to understand to explain why those designing circuits commercially would chose the commonly available and cheaper components if they can.

Scott_of_the_Arctic@lemmy.world on 03 Jul 08:24 next collapse

Astrophysicists would be happy with a 1 ohm resistor.

InternetCitizen2@lemmy.world on 03 Jul 16:46 collapse

You should see their simplified periodic table.

dejected_warp_core@lemmy.world on 03 Jul 09:46 next collapse

Watching people repair old electronics on Youtube has opened my eyes to the realities of real-world electrical engineering. In short: it’s all about tolerances.

A power supply may have a nominal voltage of 5V, but anything from 4.8 to 5.2 is a-okay. Why? Because your TTL components downstream of that can tolerate that. Components that do 5V logic can define logic zero as anything between 0 and 0.8 volts, and logic one as low as 2 volts. That’s important since the whole voltage rail can fluctuate a lot when devices use more power, or draw power simultaneously. While you can slap capacitors all over the place to smooth that out, there’s still peaks and dips over time.

Meanwhile, some assembly lines have figured out how to aggressively cost-reduce goods by removing whole components from some circuits. Just watch some Big Clive videos. Here, the tendency is to lean heavily into those tolerances and just run parts hot, under/over powered, or just completely outside the published spec because the real-deal can take it (for a while). After all, everything is a resistor if you give it enough voltage, an inductor if the wire’s long enough, a capacitor if the board layout is a mess, and a heatsink if it’s touching the case.

psud@aussie.zone on 03 Jul 09:55 next collapse

And your LEDs will last a lot longer if you remove one of those two resistors

UnrepententProcrastinator@lemmy.ca on 03 Jul 11:17 collapse

The way I got 100 in a lab once (electrical engineering) was by not using inductances in a frequency filter because their +/- is shit.

Aceticon@lemmy.dbzer0.com on 03 Jul 10:33 next collapse

This is EXACTLY how it went for me when I moved from a Physics to an Electronics Engineering degree at University.

Also, the trying to understand how the various circuits worked from the point of view of “electrons moving” was a hard to overcome early tendency (even simple things like LC circuits, for example, are only really understandable as ressonant stable states and for complex circuits you really have to go higher levels than “electrons” to be able to understand then in any reasonable amount of time).

On the upside when we got to things like how tunnel effect diodes worked, the whole thing was just obvious because of having had an introduction to Quantum Mechanics in the Physics degree. Also the general stuff about how semiconductor junctions work is a lot more easy to get if you come from Physics.

(In summary: Physics really helps in understanding HOW the various components in Electronics work, but doesn’t at all help in understanding how to use them to assemble a complex structure to achieve a given objective. Curiously this also applies to Mathematics and Software Development)

TimewornTraveler@lemmy.dbzer0.com on 03 Jul 12:22 next collapse

well there’s certainly none in the chip aisle

rumba@lemmy.zip on 03 Jul 14:13 next collapse

They are, however, absolutely thrilled that the smallest resistor package is now ~ 1x the plank length on the narrow side.

Madison420@lemmy.world on 03 Jul 17:45 next collapse

There is though. Iirc up to 15 digit subohm precision trimmed resistors are a thing just an uncommon and extremely expensive thing.

Venator@lemmy.nz on 05 Jul 01:19 collapse

Most physicists I’ve met would just use a 5.6 ohm resistor, or whatever they have on hand within an order of magnitude 😅