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Why do electronic components have such odd values? (2021)

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Re: Why do electronic components have such odd values? (2021)

#41

Post by [deleted] »

nomel wrote: post #31
thornewolf wrote: post #8

Earlier quoted context omitted.

tolerance should actually go down since the errors help cancel each other out. reference: https://people.umass.edu/phys286/Propagating_uncertainty.pdf disclaimer: it will be a relatively small effect for just two resitors aleph's comment is also correct. the bounds they quote are a "wost-case" bound that is useful enough for real world applications. typically, you won't be connecting a sufficiently large number of re…

> tolerance should actually go down since the errors help cancel each other out. Complete nonsense. The tolerance doesn't go down, it's now +/- 2x, because component tolerance is the allowed variability, by definition , worst case, not some distribution you have to rely on luck for. Why do they use allowed variability? Because determinism is the whole point of engineering, and no EE will rely on luck for their design…

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Re: Why do electronic components have such odd values? (2021)

#43

Post by eternityforest »

Workaccount2 wrote: post #22

Wikipedia has a nice table of these values that I actually have printed out and hanging above my bench. https://en.wikipedia.org/wiki/E_series_of_preferred_numbers#... The fact of the matter is that nowadays, E96 series resistors are readily available and dirt cheap. And if you need more precision than that, you either don't know much about electronics or you know a whole lot about electronics, heh.

I'd say if you need more than E3, you either know a lot of not much, unless you're into analog.

I've done stuff that needs high precision resistors, but usually the specific value isn't that important, just that it's a known repeatable value.

Re: Why do electronic components have such odd values? (2021)

#44

Post by klodolph »

Workaccount2 wrote: post #22

Wikipedia has a nice table of these values that I actually have printed out and hanging above my bench. https://en.wikipedia.org/wiki/E_series_of_preferred_numbers#... The fact of the matter is that nowadays, E96 series resistors are readily available and dirt cheap. And if you need more precision than that, you either don't know much about electronics or you know a whole lot about electronics, heh.

Yes—although E96 is cheap, I’m still very fond of E12. You get to keep less stock. I’ll even use two resistors rather than use something outside E12, most of the time. Maybe it’s habit?

Hell, I don’t even think all of E12 is necessary. I’ll stick to E6 most of the time.

Re: Why do electronic components have such odd values? (2021)

#45

Post by jjmarr »

nomel wrote: post #31
thornewolf wrote: post #8

Earlier quoted context omitted.

tolerance should actually go down since the errors help cancel each other out. reference: https://people.umass.edu/phys286/Propagating_uncertainty.pdf disclaimer: it will be a relatively small effect for just two resitors aleph's comment is also correct. the bounds they quote are a "wost-case" bound that is useful enough for real world applications. typically, you won't be connecting a sufficiently large number of re…

> tolerance should actually go down since the errors help cancel each other out. Complete nonsense. The tolerance doesn't go down, it's now +/- 2x, because component tolerance is the allowed variability, by definition , worst case, not some distribution you have to rely on luck for. Why do they use allowed variability? Because determinism is the whole point of engineering, and no EE will rely on luck for their design…

> Statistically you're correct,

The Central Limit Theorem (which says if we add a bunch of random numbers together they'll converge on a bell curve) only guarantees that you'll get a normal distribution. It doesn't say where the mean of the distribution will be.

Correct me if I'm wrong, but if your resistor factory has a constant skew making all the resistances higher than their nominal value, a bunch of 6.8K + 6.8K resistors will not on average approximate a 13.6K resistor. It will start converging on something much higher than that.

Tolerances don't guarantee any properties of the statistical distribution of parts. As others have said, oftentimes it can even be a bimodal distribution because of product binning; one production line can be made to make different tolerances of resistors. An exactly 6.8K resistor gets sold as 1% tolerance while a 7K gets sold as 5%.

Re: Why do electronic components have such odd values? (2021)

#47

Post by MeteorMarc »

Workaccount2 wrote: post #22

Wikipedia has a nice table of these values that I actually have printed out and hanging above my bench. https://en.wikipedia.org/wiki/E_series_of_preferred_numbers#... The fact of the matter is that nowadays, E96 series resistors are readily available and dirt cheap. And if you need more precision than that, you either don't know much about electronics or you know a whole lot about electronics, heh.

E12 is also great for older users who do not have the keen eyesight anymore to read the 1% codes with certainty without using tools.

Re: Why do electronic components have such odd values? (2021)

#48

Post by eternityforest »

tshaddox wrote: post #39

These sometimes end up being useful in UI/graphics work too. And the math/code is dead simple! https://gist.github.com/tshddx/8341d1bdbe2f83ed4e2c26bc48faf...

I like the 5-smooth numbers and related sequences, because they include a lot of numbers that are very common in engineering
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