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What would be the purpose of using a colour code for resistors instead of just printing their values?

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    \$\begingroup\$ @jsotola I'm assuming OP is indian and it has to do the way english is taught there. I find them using "doubt" as a catch-all word for "general lack of knowledge" instead of something specific they have in mind that they are uncertain about. \$\endgroup\$
    – DKNguyen
    Aug 11, 2020 at 3:39
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    \$\begingroup\$ @Chuck problem with printing text on an axial resistor body is that the info would have to be printed at least 3 or 4 times to ensure that it could be read when the resistor was installed in a circuit board ... surface mount components have a top side, so it makes them a good candidate for printed text \$\endgroup\$
    – jsotola
    Aug 11, 2020 at 3:45
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    \$\begingroup\$ Without the color code how would we know what bad boys do? (Not to mention Violet.) \$\endgroup\$
    – Hot Licks
    Aug 11, 2020 at 18:00

4 Answers 4

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A long time ago, the technology did not exist or was too expensive to print such small text on parts.

Also, you can read coloured rings no matter what angle you are looking at the resistor from or how it is mounted, but as someone who has trouble telling similar colours apart this is useless and I don't really buy it.

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    \$\begingroup\$ As someone in possession of old PCBs with lots of resistors with printed values, I can tell you that "read from any angle" is no myth. When the printed value is face down on the board, you have to remove the part (at least on one end) to read the value. Murphy's law almost guarantees that the value will be face down on every part you need to check. \$\endgroup\$
    – JRE
    Aug 11, 2020 at 6:01
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    \$\begingroup\$ Many years ago, the Royal Navy blocked those with colour blindness from electronics positions on the grounds that (at the time) the ability to read colour codes was critical. \$\endgroup\$ Aug 11, 2020 at 11:09
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    \$\begingroup\$ Back in the 30's and 40's it was very common for radio manufacturers to use "non-standard" resistor values (70k, 25k, etc). The urban legend goes that those values were chosen because the factory lighting was so poor that they used the ones with more distinct color bands. No evidence to support this, just a story the "old timers" tell! \$\endgroup\$
    – 640KB
    Aug 11, 2020 at 12:38
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    \$\begingroup\$ Manufacturability is definitely the major reason. Even today nobody wants to pay 0.9¢ for a resistor if it can be had for 0.7¢ instead. Painting a stripe is a bit simpler than printing a tiny character, and you'd be amazed how much people really want to save those 0.2 cents. \$\endgroup\$
    – J...
    Aug 11, 2020 at 16:52
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    \$\begingroup\$ @JRE When I say I don't buy it, I mean I don't believe that being able to view from any angle was the driving reason why text was not used. \$\endgroup\$
    – DKNguyen
    Aug 11, 2020 at 17:23
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Some leaded resistors, particularly precision ones, are marked with the value.

enter image description here

Putting color bands on the resistor allows the value to be read regardless of the orientation, and very quickly for a skilled person.

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    \$\begingroup\$ Ah, I am a poor old hobbyist and I can "scan" colour rings 10 times faster than using a magnifying glass to read numbers and letters. Actually all my life I have not never seen any expensive resistor with marked value, because I am poor. :) \$\endgroup\$
    – tlfong01
    Aug 11, 2020 at 3:09
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    \$\begingroup\$ @tlfong01 My theory is that they think poor people are illiterate, therefore something must be done so poor people can read the resistor values. \$\endgroup\$
    – DKNguyen
    Aug 11, 2020 at 4:16
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    \$\begingroup\$ @DKNguyen so poor people might be illiterate, but must necessarily be colorate :) \$\endgroup\$
    – Ruslan
    Aug 11, 2020 at 11:10
  • \$\begingroup\$ It's okay if you're assembling a board, but it kind of sucks when you are trying to read the value printed on the resistor, but it's on the side next to the PCB, and the board is conformally coated. \$\endgroup\$ Aug 11, 2020 at 13:52
  • \$\begingroup\$ @Ruslan Ahhh, but you pass pass down coloracy to to future, poor and illiterate generations through song and dance via the nursery rhyme. \$\endgroup\$
    – DKNguyen
    Aug 11, 2020 at 18:21
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Once you go to more modern surface mount parts, it is more common than not to have the resistance value simply printed on the top for the larger (and thus more human solderable) sizes:

enter image description here

Through hole parts don't do that because they're old and in the old days precision manufacturing wasn't as good as it is now.

Surprisingly, this (edit: labeling) never caught on for capacitors (edit: SMD capacitors), even though resistance is much easier to measure.

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    \$\begingroup\$ There were a number of vintage axial capacitors that used color bands to denote value, "Bumblebee" (Bumble-bomb) for example. Some vintage mica capacitors used dots with a similar scheme too. \$\endgroup\$
    – 640KB
    Aug 11, 2020 at 12:54
  • \$\begingroup\$ Back in the day, used a lot of these Philips film capacitors. \$\endgroup\$ Aug 11, 2020 at 13:54
  • \$\begingroup\$ @640KB Sorry, I meant labeling SMD caps never caught on. Always funny to see a bigger 1206 unlabeled cap but a microscopic 0603 with the resistance clearly written on it. \$\endgroup\$ Aug 11, 2020 at 15:24
  • \$\begingroup\$ For quality control purposes it is important to have a marking as AOI is often the primary QC , of course tiny parts can't have this so advanced SMT tools will compare images of each part as it is being placed to known reference models of the part. This also catches upside down and backwards parts (when it matters) as every once in a while the part is in the reel wrong \$\endgroup\$
    – crasic
    Aug 11, 2020 at 17:35
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    \$\begingroup\$ @user1850479 is it mostly a property of the material,l believe. Ceramic is either a more difficult or more expensive to label, industry would love labeled caps it's one of the biggest QC shortfalls for most manufacturers \$\endgroup\$
    – crasic
    Aug 11, 2020 at 17:37
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In some OLD resistors I once rescued from tube radios as a kid, the BED_coded resistors were only readable from the top.

Because the code was

  • BODY color

  • END color

  • DOT color (only visible from the top)

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