- cross-posted to:
- science_memes@mander.xyz
- lemmyshitpost@lemmy.world
- cross-posted to:
- science_memes@mander.xyz
- lemmyshitpost@lemmy.world
cross-posted from: https://lemmy.world/post/27589038
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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.
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.
This guy electrons!!! <3
Welcome to the field of engineering! Your first lesson will be; “Tolerances and you”!
+/-15 %? Good enough!
If it fits, great! If it doesn’t, you didn’t use enough tape.
A failed inspection is just an invitation to use a different method until it passes.
As a calibration technician, this makes me hurt. Lol.
pi == 3
Cringes in Monte Carlo.
Pi is roughly 5.
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.
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 justxfor a sufficiently smallx.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.
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?
Bet that one was started by all those dastardly programmers that wear knee high socks!
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.
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.
Second lesson: Pi is around 3.
Where are the spherical cows?
would be a great band name
No no no no, I think you got that wrong. Chickens are spherical, cows on the other hand are cuboid. And humans are cylindrical.
Chickens, cows, and humans all are toroids. True story.
Can confirm, am shaped like a weird donut
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.
The humble potentiometer:
The least reliable resistor. Not to mention the trial-and-error getting it close enough to the target value.
linear potentiometer 100% pain, but Multi meter and rotary or digital potentiometer could be simple enough.
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?
Good info. Cheers mate!
I kinda wonder if there’s a specific reason for that number other than just being an ass.
2pi
would start with 6.28
He’s bad at math/estimating
Tau
wau
well there’s certainly none in the chip aisle
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)
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.
The way I got 100 in a lab once (electrical engineering) was by not using inductances in a frequency filter because their +/- is shit.
And your LEDs will last a lot longer if you remove one of those two resistors
You’re getting a 10 ohm resistor and liking it.
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.
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.
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.
just get a variable resistance, aka a potentiometer, and have fun adjusting it to get that value.
They are, however, absolutely thrilled that the smallest resistor package is now ~ 1x the plank length on the narrow side.
Astrophysicists would be happy with a 1 ohm resistor.
You should see their simplified periodic table.
There is though. Iirc up to 15 digit subohm precision trimmed resistors are a thing just an uncommon and extremely expensive thing.
Most physicists I’ve met would just use a 5.6 ohm resistor, or whatever they have on hand within an order of magnitude 😅
tau
