Why resistor color codes?
I once worked with an engineer that often checked his resistors with a multimeter before use. I just assumed that he was just being careful (certainly more careful than I…). Then one day, he asked me to identify a certain resistor — it was a 2.2K resistor with 2 or 3 shades of red. He then explained that he was color blind and the different shades of grey appeared confusing so he could not reconcile the banding with the ohmmeter reading. I had to agree with him — that device was a real “sleeper.” Since then, I have run across a few with off color banding that made me confuse **K devices with **10K devices and vice-versa.
Yes, I learned the numbers for the colors — simply in the order of the colors of the rainbow, but actually reading the color code is something that I did not really study and I suspect that most others learned the same way. As a teenager, my first breakthrough came when I picked up a resistor and said to myself: “this is a 1K resistor because it looks like one I was using in another circuit and I remember its value.” Wow, what a concept! The other values fell into place quickly. Soon, I was able to look into my junk box for a specific pattern without thinking.
Standard 5% resistor values
Standard 5% Resistor Values (100 – 910Ω)
100 110 120 130 150 160 180 200 220 240 270 300
330 360 390 430 470 510 560 620 680 750 820 910
Note that there are only 24 values in each decade — and you probably already know most values.
5 & 6 band resistors
While I quickly learned the very useful 4band resistor color codes, I never really mastered the 5 and 6band versions — yes, I can identify a few common patterns, but anything new is a problem. To begin with, there are simply far too many values to recognize patterns—7decades and some 96 per decade for 1% values and double that for 0.5% values. Additional variations in the tolerance band add still further complications. My brain is already dangerously close to running out of memory and I would rather learn “neat” stuff rather than to stuff it with this sort of stuff. The next issue is also very basic: which end do I start with? My recommendation: Use an ohmmeter or the DigiKey Resistance Calculator!
Even resistances values now available
Now, even resistance values are available. Years ago, when I needed a 50K resistor, I was forced into a 49.9K 1% value because that is how the 1% table “panned out.” Yes, that was close enough, but now DigiKey actually offers a 50K along with many other even resistance values as well.
Why so many resistor values in comparison with capacitor values?
Perhaps you have noticed that while almost any value capacitor is available, few odd values are actually used. The reason is simple: resistors are far less expensive and far more precise than capacitors. As a result, it is more cost-effective to standardize on certain capacitor values and handle timing variations etc. via using odd value resistors.
Undocumented words and idioms (for out ESL friends)
neat – idiom – good or useful information—cool stuff
cool – idiom – adjective — interesting, good, attractive (historic: cold temperature)
panned out – idiom – how something works out in practice—an allusion to “panning for gold” in a riverbed—that is what you get