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I always wondered why color coding is still used on resistors in 2014.

Here is Wikipedia's word on the original reason why :

Colorbands were commonly used (especially on resistors) because they were easily printed on tiny components, decreasing construction costs. However, there were drawbacks, especially for color blind people. Overheating of a component, or dirt accumulation, may make it impossible to distinguish brown from red from orange. Advances in printing technology have made printed numbers practical for small components, which are often found in modern electronics.

However, like pointed out in this quote, printing small numbers on electronic is now quite an easy thing (or so it seems) and it would, in my opinion, be much more convenient, especially for colour-blind people.

Is there reason why we still use colour coding on resistors in 2014?

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The only reason I can think is that I can read color codes without a magnifying glass. I've seen lettered markings on 1/8 watt and 1/4 watt resistors, and they are very small. Colored bands on the same size part are much larger and easier to read. (Actually, I don't need a magnifying glass. I'm so near sighted that I just need to take off my glasses and hold the parts up close to my eyes. Still, I don't have to do that to read color codes.) I can read markings 0603 size parts. I think they stop marking parts below 0603. –  JRE Aug 21 at 8:42
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@JRE I would also not be surprised if the color coding is not only more easily seen but requires less thought to distinguish parts (i.e., friendlier to pattern recognition than a series of numbers) at least when the diversity of parts of similar size and shape is small. This might be useful when prototyping (when the convenience of using fewer part types might be more important than the cost, durability, or efficiency of the result). (Just a guess; I have never designed or developed electronics.) –  Paul A. Clayton Aug 21 at 13:07
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The equipment used for making axial-lead resistors was probably made thirty years ago! –  Spehro Pefhany Aug 21 at 14:20
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Have to disagree here - I'm colour blind and the red/orange/brown distinction especially is a nightmare (nevermind after 'overheating' per above). –  Ollie Ford Aug 21 at 19:12
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That I can answer in one word - TRADITION! –  Bob Jarvis Aug 22 at 11:28

4 Answers 4

up vote 11 down vote accepted

My opinion.

Through hole parts are often cylindrical. Hence applying stripes is simple in production. Resistors may have five stripes, tolerance, 3 significant digits, and order of magnitude. That is a lot of information to write, "22811" 22.8ohm 1%? In san-serif font what is 88818? It would be possible to read 1, 2 or 5, 6 or 9, and 8 rotated, i.e. upside down, and be confused.

As pointed out by JRE, a letter in the text is used to help ensure the text is the correct way round, e.g. 22K8.

However, while colour blindness is a problem for stripes, dyslexia is for text. I know of people who would write 'k' backwards without noticing.

Edit: There are many written languages which do not use the Arabic digits (in fact, Arabic digits is a misnomer, because the Arabic digits are different shape or value to commonly recognised digits in 'the west'). So printing digits isn't automatically better than a level of indirection via colour which is language independent.

One pretty thing about 7 of the resistor colour codes is it is in the same sequence as the colours of the rainbow (in some cultures), so many people learn that part of the sequence as children.

The through hole cylindrical part could have its wires bent in any direction, and coloured stripes are still legible from any direction.

If written text is applied in only one location, the part value may be obscured or invisible when it is in circuit. That would be a disaster for repair and inspection.

Hence, written text will have to be applied on all sides in order to be legible, which may well be more difficult and hence expensive to produce, and still awkward to read. Stripes don't suffer from this orientation problem. Stripes are simple to use.

Manufacturers have already invested in machinery to product components with colour stripes.

Where is the competitive advantage? There needs to be 'new' money to fund the change over to printed numbers, or it won't happen. I don't see anyone financial benefit.

I haven't seen any new robots doing pick & place with through hole parts. It is hard to imagine such a robot would have enough financial advantage over SMT to make it worthwhile.

The assembly staff who use the components will have to be retrained, and what benefit does the assembly company get?

Through-hole with printed numbers would have to show big benefits to replace coloured rings. AFAIK, SMT has displaced through-hole in the majority of products; robots are cheaper than labour costs humans for mass production.

"Show me the money" - It seems a very tenuous benefit to printing numbers vs lots of cost, especially when the investment has been made already, in a shrinking sector of industry.

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The through hole parts I've seen that had printed values were only printed in one place. Depending on how it landed, some of the markings were underneath the part and couldn't be read - I had to unsolder one end to read the value. Score another point for color bands. –  JRE Aug 21 at 10:33
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I don't know why you say "Robots don't do pick & place with through hole parts" -- pick and place was invented long before SMD became common. –  Dave Tweed Aug 21 at 11:50
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@ChrisH: Electrolytics are usually insulated with a heat-shrink wrapper, which is printed on before being applied to the part. –  Dave Tweed Aug 21 at 15:42
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Axial through-hole parts are generally supplied on reels or in "ammo packs", with a tape at each end connecting all the parts together (so the parts form the "rungs" of a "ladder"). As such, machines don't "pick and place" them, but instead use a die to cut and bend the leads and force them into the holes on the board (for each lead, the machine would have an open-half-code opening which would be placed against the hole, so once the lead was forced into the cone, its elasticity would hold it against the cone as it was coerced downward until it went through the hole). –  supercat Aug 21 at 16:36
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...in a way that surface-mount parts cannot. –  supercat Aug 23 at 19:03

The reason for using color bands on through-hole (axial) resistors is simple -- when they are inserted into the PCB, you can't guarantee their orientation -- there is no top or bottom. So you need a way to mark the value so it can be seen no matter how the part is oriented with the board. Color bands are perfect for this.

For this reason, I don't expect to see color bands disappearing from through-hole resistors.

With surface mount parts, there is a top and bottom, so the parts can have the value stamped on the top.

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+1 - good point! Not so obvious, yet still obviously true... –  vaxquis Aug 21 at 12:06
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just print the number three times... –  nbubis Aug 21 at 20:46
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Axial capacitors still have text printed on them, or radial capacitors with legs bent 90 degrees. They just print the value multiple times. I think resistors just stick with tradition, nothing more. –  MoJo Aug 22 at 10:21
    
@MoJo Just about all axial electrolytics, even small values like 1 or 2 µF are much larger than a 1/8 watt resistor (4.5mm dia x 10mm L for a 1 µF cap, 1.7mm dia x 3.3mm L for the resistor). –  tcrosley Aug 23 at 11:44
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@MuhammadUmer -/+ of a resistor? Do you mean capacitor? –  tcrosley Aug 23 at 21:34

My guess (and it is just that) - colour bands are easy to apply with a basic machine (rollers dipped in paint, component rolls past) and if the machine works, why change it?

The alphanumeric markings on things like SMD devices require laser-etching, printing or similar. I'd further guess that either the laser etching / printing is already an inherent part of the production of SMD components, or that it's easier than trying to colour band or print or whatever onto a flat/square component, or that when they developed the production system they decided it was no great extra effort to move from colour bands to alphanumerics.

TBH most components used, by bulk sales, will be fed in reels into a pick & place machine, as long as the label on the reel or package is correct the machine is not reading colour codes or part numbers.

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I would say that mass production also plays a part in why there are still Color bands as well.

There is probably a lot of these still left from some company mass producing them a long time ago, and if they are still good and usable why throw them away or attempt to print numbers on them, there is no need to change something that people are already acquainted with, that still serves the purpose.

Otherwise, I would say it is because they are round and have no top or bottom like @tcrosley said.

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