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Comment by codeflo | Hacker News Reader

The “coverage” explanation given by the top answer doesn’t make a whole lot of sense. With the manufacturing tolerances involved (especially historically when those values were chosen!) the idea that 22 and 47 gives more useful combinations than 22 and 46 is numerology, not engineering.

Wikipedia only says that the deviation is for “unknown historical reasons”. Maybe a deep explanation doesn’t exist, and it’s a simple historical error that was propagated?

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Ultra-precise resistor values have been possible for as long as there have been good meters. It turns out that's a very long time ago.

The numerology makes a lot of sense if you are working with 0.1% tolerance parts. Lower tolerances have actually gotten more popular as electronics have become more cost-sensitive.

Possible, sure, but isn't the origin of the E12 series, as opposed to using e.g. the Renard R10 series, for specifying ±10% precision parts?

1 ±10% is 0.9 to 1.1

1.2 ±10% is 1.08 to 1.32

1.5 ±10% is 1.35 to 1.65

1.8 ±10% is 1.62 to 1.98

2.2 ±10% is 1.98 to 2.42

And so on.

> Ultra-precise resistor values have been possible for as long as there have been good meters. It turns out that's a very long time ago.

It's not about metering but stability of the resulting value. 1% or 0.1% doesn't do you much good if few degree temperature change gets it out of spec. Now temperature coefficent is an additional spec on the spec sheet but by definition you kinda need low drift to go in pair with high precision

> The numerology makes a lot of sense if you are working with 0.1% tolerance parts. Lower tolerances have actually gotten more popular as electronics have become more cost-sensitive.

Lower tolerances have just become cheap. Back when I was a kid there was significant difference in price between 1% and 5% resistors. Now they cost basically same (for low power ones at least) so why not ? [1]

You also don't really need that many precision parts in the first palce.

Where before in say a power amplifier you had say an analog preamp driving power IC (or outright discrete power amplifier) you had to have a bunch of precise resistors (or someone tweaking a pot on the production line) to keep the gain same in both tracks. Now you just slap a D-class chip that takes line in and outputs power and you're done, and the few % variance in power supply caps or output filter doesn't matter much.

* [1] https://eu.mouser.com/c/passive-components/resistors/?case%2...

On price - you are looking at low quantity. Buy a few million of them from a manufacturer, and you will find the 5% ones still significantly cheaper (even at standard temp coefficients and power levels). That's why new 5% and 10% resistor products are still sold.

Note that the second part of the argument was that the quantities needed are low. I'd go even further than the GP: even in the "old days" my understanding is that the number of precision parts needed was very low. Most circuitry is of the "pick a component value in this order of magnitude" variety, even on sensitive hardware. Only the handful of parts where it really matters need precision.

But, whereas previously you might spec 5% for a few resistors and 10% for the bulk, now it's no longer worth the added line on your BOM.

> Buy a few million of them from a manufacturer, and you will find the 5% ones still significantly cheaper

That just ain't true. 5% are not really used (at least with consumer electronics). 1% and 5% difference is very tiny, even across few millions.

> That's why new 5% and 10% resistor products are still sold.

If you go on digikey and search for 10% you will not find very many compared to 1%

> you had to have a bunch of precise resistors (or someone tweaking a pot on the production line) to keep the gain same in both tracks

Or match them by hand before they’re placed.

But if you need 0.1% tolerance resistors and the circuit diagram requires a 13.3 (±0.1%) kΩ resistor, you can just order one ...?

I have a hard time imagining situations like "We need a very precise 57kΩ (±0.5kΩ or about 1%) resistance but we can only get three precise resistors: 10kΩ, 22kΩ, and 47kΩ! Oh thank god we can connect 10kΩ and 47kΩ, if the last one was 46kΩ we would have been in trouble."

In terms of scale, you cannot simply order a larger factory. It has opportunity cost.

There are a lot of times when even the 1% and 0.1% ladders don't have the value you need, and you can usually construct a combination of only two of them to get that value, thanks to the way the ladders are set up.

Note that the linked document https://www.govinfo.gov/content/pkg/GOVPUB-C13-f5fea679df4c3... doesn’t just apply to resistors or electrical components. It is a general framework for deriving “preferred” numbers.

Main reason are costs for mass production, and nuances of technology, that electronic components usually made in very huge batches, then distributed to distribution network and lie on storage up to tens years.

So manufacturers made series of agreements, like "in 2020-2025 make e3; in 2025-2030 make e12".

Expensive high precision parts, are not in this scheme, they allocated by direct requests, like Toshiba manufacture high-end transistors, and order for them high-end resistors with some exact value.

As I read it, rationalization is one of the core reasons.

Similarly I find the no odd numbers argument unconvincing, again because of the tolerances and also because placing two of the resistors in parallel yields odd values for 10 and 22 and almost 15 (14.9855) for 22 and 47.

Also you can just use one magnitude lower resistor... 10 isn't odd but 1 is.

Honestly the explanation looks like someone tried to reverse-engineer a mistake into logic.

But there is no reason why 0 tolerance resistor couldn't exist or even being very useful for certain application like voltmeter.

If you want 0% tolerance, you can hand-match.

No-one needs 0% tolerance.

Sure, you can handmatch. If the thermal radiation of your hands wouldn't affect the measurement.

This is actually a real problem with semiconductors. I often need carefully matched sets of transistors and diodes, and a quick and easy way to get them "good enough" is just to measure either a diode or the B-E junction of the transistor with a multimeter in "diode check" mode. I pin the paper strip to a piece of wood and let the temperature stabilise for about half an hour before I start, and only touch the component with the meter probes.

You can try this yourself. With any given 1N4148 you'll see the Vf indication on the meter change as the microscopic current warms the junction up a tiny bit. If the room (and thus the diode) is fairly cold, it can detect the heat from your finger at about 1cm away.

The reason you can not build a 0% tolerance resistor is the laws of physics. A very high precision resistor can certainly be build but it will never be perfect. Increasing precision has a cost to it. For normal resistors the shape and thickness of the film of resisting material is calculated and the tolerance is mainly dictated by the precision of the manufacturing process. Increasing this precision of the process adds cost. High precision resistors can be trimmed to specification. When you manufacture the resistor with a lower resistance you can use a laser to trim some of the resistive material away. This is an extra step and adds extra cost. While this can be very precise you are limited to what you can measure and there is a limit to that. Also precision is limited by environmental factors like heat, humidity and aging.

That's also how many higher end analog chips are made, just blast it with laser till it fits tolerance. Making a bunch of chips in less precise process then trimming them chip by chip ends up cheaper than going to more expensive processes.

We are saying the same thing. For most applications, 5% tolerance is fine if could be cheaper. But for some applications it is worth the extra cost.

It sounded like you were saying that a 0 tolerance resistor would be worth the extra cost, and the reply is pointing out that a 0 tolerance resistor is not actually possible anyway, and as you approach 0, the cost increases beyond whatever your limit is.

It would seem pretty pointless to try to nail the resistor to within 0% tolerance when the solder bridges, wire that connects them to the circuit will have resistance.

You can get really high precision for a resistor at the silicon level but as for a regular resistor, the most you can do is buy the best TCR value you can and laser trim it to the exact spec. You can also buy hermetically sealed that have extremely low TCR and tolerances but they are expensive as hell and are relatively massive. If you can control the temperature of the board really well, you can hit very precise resistance values but again, expensive and not possible for all applications.

Overall, it's much easier to understand where your noise bottlenecks are in your system and cheap out on the parts that won't contribute to any reduction. Like if your ADC has a bit resolution of only 1uV, worrying about noise at the nano volt is just a waste of money.

> But there is no reason why 0 tolerance resistor couldn't exist

I think the laws of physics is a pretty good reason.

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