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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)

#101

Post by londons_explore »

hathawsh wrote: post #93
picture wrote: post #87

Earlier quoted context omitted.

Have you tried 10 kΩ for LED and FET pull down? 100 Ω sounds like way too much current for modern LEDs. I often end up using 100 kΩ especially for green LEDs. They are very visible under indoor lighting even with 1 MΩ and 3.3 V supply. For pulling down FETs, you want something in the range of 10 kΩ. 10 MΩ sounds way too high, which makes your circuit sensitive to being touched or affected by moisture, especially if t…

Are you sure all those numbers are in the right ballpark? With a 3.3V supply and a 1 MΩ resistor, the most current you can get from that circuit is in the neighborhood of 3μA, and that's ignoring the LED voltage drop. I would think the LED won't be visible until you're around the mA range. Or are some LEDs visible in the low μA range?

human eyes are logarithmic and can easily see microamps.

In fact, just hold an LED between your fingers in a dark enough room and you'll sometimes see them glow from stray magnetic fields inducing enough current in your body to light them.

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

#102

Post by nomel »

Dylan16807 wrote: post #83
nomel wrote: post #76

Earlier quoted context omitted.

Very true, I was writing as absolute value, not % (magnitude is where my day job is). My point still stands: it is complete nonsense that tolerance goes down.

They said it "should" go down, but that another comment saying the worst case is the same is "also correct". I do not see any "complete nonsense" here. I suppose they should have used a different word from "tolerance" for the expected value, but that's pretty nitpicky!

I'm sorry, but it's incorrect, as stated. It's a false statement that has no relation to reality, with the context provided.

Staying the same, as a percentage, is not "going down". If you add two things with error together, the absolute tolerance adds. The relative tolerance (percentage) may stay the same, or even reduce if you mix in a better tolerance part, but, as stated, it's incorrect.

It's a common misunderstanding, and misapplication of statistics, as some of the other comments show. You can't use population statistics for low sample sizes with any meaning, which is why tolerance exists: the statistics are not useful, only the absolutes are, when selecting components in a deterministic application. In my career, I’ve seen this exact misunderstanding cause many millions of dollars in loss, in single production runs.

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

#103

Post by Dylan16807 »

nomel wrote: post #102
Dylan16807 wrote: post #83

Earlier quoted context omitted.

They said it "should" go down, but that another comment saying the worst case is the same is "also correct". I do not see any "complete nonsense" here. I suppose they should have used a different word from "tolerance" for the expected value, but that's pretty nitpicky!

I'm sorry, but it's incorrect, as stated. It's a false statement that has no relation to reality, with the context provided. Staying the same, as a percentage , is not "going down". If you add two things with error together, the absolute tolerance adds. The relative tolerance (percentage) may stay the same, or even reduce if you mix in a better tolerance part, but, as stated, it's incorrect. It's a common misundersta…

It only stays the same if you have the worst luck.

> You can't use population statistics for low sample sizes with any meaning

Yes you can. I can say a die roll should not be 2, but at the same time I had better not depend on that. Or more practically, I can make plans that depend on a dry day as long as I properly consider the chance of rain.

> In my career, I’ve seen this exact misunderstanding cause many millions of dollars in loss, in single production runs.

Sounds like they calculated the probabilities incorrectly. Especially because more precise electrical components are cheap. Pretending probability doesn't exist is one way to avoid that mistake, but it's not more correct like you seem to think.

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

#104

Post by jessriedel »

throw0101d wrote: post #34

This part is the thing that made me understand the numbering series: > […] Continuing this trend, rounding as needed, and we end up with the series 10, 15, 22, 33, 47, and 68. Components built to the E6 standard have a 20% relative error tolerance, and if we look at the values again we’ll see a trend. Starting with 10 again and adding 20% error we end up with 12. Moving to 15 and subtracting 20% we get… wait for it……

Seems easier to me to say they are logarithmically distributed, rounded to 2 digits.

Like yes, this means that if your manufacturing tolerances are typically some percentage of the amount (more natural than an additive error) then the overlaps are nicely spaced. But a log scale means that's true for any relative allowance (manufacturing or otherwise), which is the much more natural sort. It doesn't matter if your 100-foot house is off by 1mm, but it does matter if your 1mm-thickness fork is.

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

#105

Post by e-khadem »

pclmulqdq wrote: post #99
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.

One fun thing to do when designing high-precision analog stuff (audio) was to choose component values that are about 1.5-2% off of a value in the E12 series. You can then go test a whole bunch of resistors and you will find a lot within 0.1% of each other (even within 0.01%). Everything within 1% of E12 is binned as a 1% resistor so those aren't polluting your stock. Going within 0.1% of an E12 value is a pricey resi…

Raw room temperature value isn't the only reason we use precision resistors. Some parts tend to behave more linearly at higher voltages (especially at the Meg range) and others exhibit much lower tempco's. There is also the problem of long-term stability and value change due to exposure to high temperatures during soldering.

In any case, the above trick is neat, thanks for sharing it.

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

#106

Post by _carbyau_ »

CamperBob2 wrote: post #97
londons_explore wrote: post #84

Earlier quoted context omitted.

Being a mostly-digital electronics guy, I think 0.1, 1, 10, 100, 1k, 10k, 100k, 1M and 10M is a perfectly fine series for pretty much any usecase. Sense resistor? 0.1 ohm. Resistor for an LED: 100 ohm Pull up resistor: 10k Bias resistor for some mosfet gate: 10M Voltage divider to measure the battery voltage with an ADC: two 100k resistors. It's super rare I need anything else. I hate fiddling about with switching th…

Resistor for an LED: 100 ohm Yeah, that's why I can read a book by the blue LEDs on my alarm clock...

https://www.3m.com/3M/en_US/p/d/b40068069/

Depending on the colour bleed though. It may wipe out all visibility of the clock numbers.

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

#107

Post by Liftyee »

CamperBob2 wrote: post #97
londons_explore wrote: post #84

Earlier quoted context omitted.

Being a mostly-digital electronics guy, I think 0.1, 1, 10, 100, 1k, 10k, 100k, 1M and 10M is a perfectly fine series for pretty much any usecase. Sense resistor? 0.1 ohm. Resistor for an LED: 100 ohm Pull up resistor: 10k Bias resistor for some mosfet gate: 10M Voltage divider to measure the battery voltage with an ADC: two 100k resistors. It's super rare I need anything else. I hate fiddling about with switching th…

Resistor for an LED: 100 ohm Yeah, that's why I can read a book by the blue LEDs on my alarm clock...

And to think a little dimming circuit with LDR/phototransistor (RoHS..) is practically electronics 101...

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

#108

Post by projektfu »

riedel wrote: post #70
projektfu wrote: post #21

Earlier quoted context omitted.

Unless the components are expensive, that proposition seems dubious. It's much more economical to take a process that produces everything within 12% centered on the desired value and sell it as ±20%. 100% inspection is generally to be avoided in mass production, except in cases where the process cannot reach that capability, chip manufacturing being the classic example. For parts that cost a fraction of a penny, nobo…

Actually it seems to be really the case that multimodal distribution are rather the result of batches not having a mean. So it is rather the effect of systematic error [1]. I guess it is really a myth (we did low cost RF designs back in 2005 and had some real issues with frequencies not aligning die to component spread and I really remember that bi modality problem, but I guess okhams razor should have told me that i…

Yup, forever the reason for the trim pot.

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

#109

Post by zaroth »

londons_explore wrote: post #101
hathawsh wrote: post #93

Earlier quoted context omitted.

Are you sure all those numbers are in the right ballpark? With a 3.3V supply and a 1 MΩ resistor, the most current you can get from that circuit is in the neighborhood of 3μA, and that's ignoring the LED voltage drop. I would think the LED won't be visible until you're around the mA range. Or are some LEDs visible in the low μA range?

human eyes are logarithmic and can easily see microamps. In fact, just hold an LED between your fingers in a dark enough room and you'll sometimes see them glow from stray magnetic fields inducing enough current in your body to light them.

Beautiful if true!

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

#110

Post by SamBam »

throw0101d wrote: post #34

This part is the thing that made me understand the numbering series: > […] Continuing this trend, rounding as needed, and we end up with the series 10, 15, 22, 33, 47, and 68. Components built to the E6 standard have a 20% relative error tolerance, and if we look at the values again we’ll see a trend. Starting with 10 again and adding 20% error we end up with 12. Moving to 15 and subtracting 20% we get… wait for it……

I still don't really get the overlapping tolerances, though, because each resistor is not a range, it's a single value that's somewhere in that tolerance.

He says about the cables:

> Each size of cable had a max/min rating that just overlapped it’s neighbor above and below, so every required value was covered by one or more cable.

So that means if you needed a "size 12" cable you could pick a size 10 OR a size 15, and they would both work.

But if you need a 12ohm resistor, it's possible that neither the 10 nor the 15 might work, because the 10 could be a 9 and the 15 could be a 17. So I don't really see how it connects.

To put it another way, what if we had 1000% error tolerances? Could we then get away with just a 1ohm. 1000ohm and 1Mohm resistors, because their tolerances overlap? Obviously not, so I don't see how it relates.

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