In working on the builds for Weekend Projects, we’ve been dealing a lot with resistors of different values (indicated by the color bands on the resistors themselves). Trying to figure out the values of these common components can be confusing to new electronics hobbyists, so I thought it would be helpful to share some tips and tools for identifying them.
It seems like at least once a year here on MAKE there’s a “How-To Read a Resistor” post. They’re all incredibly useful in their own ways. I, in fact, use no less than four ways to read them, depending on where I am in the world and whether I’m trying to decipher a resistor’s value, or know the value and want to find the color scheme. If you’re fortunate enough to have a Maker’s Notebook, on page 162 is the Resistor Color Codes matrix. You can cleverly hack your own notebook with markers or colored pens like this so that the grid is more colorful and easier to reference. I also keep a printed-out version of this same matrix on my workshop wall, so all I have to do is look up to figure out “violet = 7” or whatever value/color I’m hunting down. When working with beginners, I’ve found the resistor matrix to be a bit frustrating. It’s time-consuming trying to add up values in your head, and if you can’t write something down for whatever reason, it’s easy to forget. Which is why one of my favorite tools for beginners is the resistor color wheel [PDF]. I also keep a version of this pinned to my wall which I can easily spin, so when I’m looking for a 47k resistor, I quickly and easily know I’m looking for Yellow, Violet, Orange for the first 3 bands. But like I said, I have four ways to read resistors up my sleeves! The fourth is this HTML5 resistor calculator, which is incredibly handy when I’m neither in my workshop nor have my notebook with me to reference. As the name implies it only works with HTML5-compatible browsers, but all you have to do is scroll the dials into place and voila, you’ve calculated your resistor value. (NOTE: these color wheels are useful for standard four-band ‘carbon film’ resistors.)
Work with enough of the same resistors and you’ll start to memorize the color sequence and its value, but in the meantime these are some great ways to get started.
See all of the RadioShack Weekend Projects posts (to date)
16 thoughts on “The Many Methods to Reading Resistor Values”
When I was in college, I took a beginning electronics course. I was struggling with the mnemonic the instructor gave us involving “Blue Bonnets….”. I still can’t remember the thing. My seatmate leaned over to me and told me the mnemonic they gave him in the navy.
First my apologies to just about everyone.
Bad Boys Rape Our Young Girls But Violet Gives Willlingly
Black Brown Red Orange Yellow Green Blue Violet Gray White
It makes me think of General Patton: “When I want my men to remember something important, to really make it stick, I give it to them double dirty.”
I’ve been told the original was even worse: “Black boys…”
My advice to the new blood would be as follows: Don’t spend much time futzing with order memorization, because it’s easier to develop intuition about the values you’re most likely to see. Starting is as easy as memorizing the codes for three two-digit numbers, then another three.
Firstly, start by memorizing the E3 series digits (10 is brown black, 22 is red red, 47 is yellow violet) then the E6 (15 is brown green, 33 orange orange, 68 blue gray). There are others to learn, but just those six are common enough that it will save you time to know them by heart.
Secondly, learn what 1K, 10K, and 100K look like. These are also somehow incredibly common, and will help you get a grasp of the most common multipliers, which in my experience have been red (-00), orange (-k), and the occasional yellow (-0k). Later you can pick up the other three or so common values (you probably won’t use too many resistors below 100 ohms or above 47M).
Thirdly, after you have the above down, use what you’ve learned to feel out the digits. If you only know the E3 values, you already have half of the digits. If you have E6 down, you know everything except 9 (which is white).
Finally, and try to avoid using this as a crutch, if you get lost while feeling this out, note the code’s relationship to the traditional color wheel I hope they’re still teaching in elementary art: 2 through 7 are the primary and secondary colors in spectral order (e.g. orange is between red and yellow, and 3 is between 2 and 4). The lowest two and highest two are neutral colors. 0, the lowest, is black, while 9, the highest, is white. What’s left is brown and gray, to which I’d say I hope you already knew brown is 1. If not, start over. :-)
I actually just mapped this approach out in my head recently, but I wish someone had run it by me this way sooner. Thoughts?
Also good advice. I found what helped me memorize the color values was simply buying an assorted pack of resistors, then by writing the values on the paper strips that the resistors are bound in, I started to learn the color sequence. This also allowed me to use the resistors like ‘flash cards’ and I could try and guess the value, and flip it over to see if I was correct or not. Learning by doing!
How about a nicer version:
Bad Boys Race Our Young Girls But Violet Generally Wins
I actually presented that two weeks ago in a talk I did in Tarsier on Life Lessons Learned.
thank you Gary!
Resistance is Useless!
but resistors aren’t futile ;)
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