Standard Resistor Values: Why not a true geometric series?

Look inside mass-produced, non-miniaturized items like DVD players and PC power supplies and you'll invariably find cheap single-sided through-hole PCBs. The holes in those look rather like stamped than drilled.

robert

Wouldn't matter. They're still cheaper.

They're drilled, they just don't replace the bits as often, so at the end of their life cycle, the holes they make get pretty rugged looking.

Nonsense. They're PUNCHED. All in one bang, with the outline. They warm the paper-based phenolic to make it easier to punch without cracking. That's how you get a PCB for 20 cents. More tooling cost.

Best regards, Spehro Pefhany

Some of the phenolics can be punched, so very cheap, very high-volume boards are sometimes punched. I don't think FR-4 can be punched.

John

It can be. Probably shorter punch life.

Best regards, Spehro Pefhany

The first resistor standard was 50% tolerance with three steps of 1 2 5 per decade.

E6 ( 20%): 10 15 22 33 47 68

E12 ( 10%): 10 12 15 18 22 27 33 39 47 56 68 82

E24 ( 5%): 10 11 12 13 15 16 18 20 22 24 27 30 33 36 39 43 47 51 56 62 68 75 82 91

E48 : 100 105 110 115 121 127 133 140 147 154 162 169 178 187 196 205 215 226 237 249 261 274 287 301 316 332 348 365 383 402 422 442 464 487 511 536 562 590 619 649 681 715 750 787 825 866 909 953

E96 ( 1%): 100 102 105 107 110 113 115 118 121 124 127 130 133 137 140 143 147 150 154 158 162 165 169 174 178 182 187 191 196 200 205 210 215 221 226 232 237 243 249 255 261 267 274 280 287 294 301 309 316 324 332 340 348 357 365 374 383 392 402 412 422 432 442 453 464 475 487 499 511 523 536 549 562 576 590 604 619 634 649 665 681 698 715 732 750 768 787 806 825 845 866 887 909 931 953 976

E192 (0.5%) 100 101 102 104 105 106 107 109 110 111 113 114 115 117 118 120 121 123 124 126 127 129 130 132 133 135 137 138 140 142 143 145 147 149 150 152 154 156 158 160 162 164 165 167 169 172 174 176 178 180 182 184 187 189 191 193 196 198 200 203 205 208 210 213 215 218 221 223 226 229 232 234 237 240 243 246 249 252 255 258 261 264 267 271 274 277 280 284 287 291 294 298 301 305 309 312 316 320 324 328 332 336 340 344 348 352 357 361 365 370 374 379 383 388 392 397 402 407 412 417 422 427 432 437 442 448 453 459 464 470 475 481 487 493 499 505 511 517 523 530 536 542 549 556 562 569 576 583 590 597 604 612 619 626 634 642 649 657 665 673 681 690 698 706 715 723 732 741 750 759 768 777 787 796 806 816 825 835 845 856 866 876 887 898 909 920 931 942 953 965 976 988

The E192 series is also used for 0.25% and 0.1% tolerance resistors.

A couple three decades ago, I was stationed in Okinawa - a veritable treasure trove of old military surplus stuff. A friend and I used to go shop the surplus shops and get all manner of interesting stuff.

He built a 1KW final with all surplus stuff, and a 4-400A that I checked out of "bench stock". (i.e., stole from Uncle Sugardaddy. shhhh!)

I saw some kind of attenuator, or passive filter, in a box, with carbon comp resistors, and some of them actually had a V-notch filed into the side and covered with something very much like nail polish.

Cant' do that with metal film, though, can you? ;-)

For those too young to remember, back in those days all they had was carbon comp. resistors, and you would actually trim them by filing a notch into the carbon. I confused some guy at the Ham club once when I said, "Uh, yeah, you just file off some of the ohms, right? ;-)" [

Don't bother - that's chairtard of the boring - he argues with everything, especially facts.

Cheers! Rich

OK, for those of us who either didn't take that class, or slept or drank our way through it, what's a "Stastical Centroid"?

Thanks, Rich

Oh, say, 10 PPM. The closer we can get the initial worst-case ratio, the less we have to trim or pad.

John

Hahahaha! That's wonderful! Now try it for 47 ohms versus 56 ohms, at 10%. What you gain at one end of the set of discrepancies, you lose at the other, huh? ;-) In fact, if you do that test with each adjacent pair of E12 values in a decade, you'll find it "fails" in 8 out of the 12 cases: for 8 of them, 10% below than the upper value is lower than 10% above the lower value.

Cheers, Tom

Rich Grise wrote: (snip)

If you actually worked with mil resistors through the past 20 years, I would think you would have some familiarity with the ones I worked with in 1986-1987. The main visible feature of those 1/4 watt mil ones was that they had appearance (especially size) similar to that of 1/2 watt commercial ones from that time and later.

- Don Klipstein ( snipped-for-privacy@misty.com)

So far, all of my boards have had no more than 2 layers whether all-through-hole, all-SMD or the few that had a mixture of these. And ExpressPCB does not surcharge for any holes at all, only for having more than so many per square inch. I rarely run into that. The only time I ran into that with an SMD board was one with clusters of thermal vias for power devices.

- Don Klipstein ( snipped-for-privacy@misty.com)

Yep ;-)

Thick film resistor trim example....

R+ | | | | | |________ | | | | Laser Trim|_____ | | | | | | ________| | | | | | | | | R-

...Jim Thompson

The 20% values were 6 to a decade, and I have seen enough stuff from back when 10% resistors were good ones. For some reason, the middle of the decade was 33 rather than 32 (closer to the square root of 1000, which to 3 significant digits is 31.6).

Of the 5 "10% values" that are "off", 4 are in a cluster that includes

2. Though I am not sure that I blame 33 rather than 47 for that cluster of "off" values. Although 33 does look to me to be the one that is "off" the most.

As for one reason why that has occurred to me as a possibility - the middle-of-decade cluster is "off" in a direction that makes the distribution of values within a decade a little closer to linear. One of my brothers asked me why most of the values within a decade are so low, as in less than 50? My response was that they were close to a logarhythmic pattern (logs close to evenly spaced, percentage change from one to the next close to constant), and if they best-fit such a logarhythmic pattern, many of the ones in the middle of the decade would be a bit lower!

- Don Klipstein ( snipped-for-privacy@misty.com)

One of the first circuits I made at the school electronics club was a stylophone[1]. The original design had a preset pot for each note; the teacher suggested that it would be cheaper to file down carbon resistors.

He kept an abrasive (non-metallic) "V" file specifically for this purpose. Being non-conducting, it could be used on a live circuit without the resistance being affected by its presence. Thus the stylophone was "tuned", the pitch dropping as the notch grew deeper.

Said the idiot that got beat up in a bar, and claimed it was a bike crash.

More like a biker crashed his fist into your face.

If that's not the case, it should be. If you like, it could be, pussy.

Bwuahahahah!