Thursday, January 7, 2010

Chapter 1 - Exercise 3

So now we're going to get to play around with resistors and LEDs for a bit.

This exercise was a good one for me because I learned to trust my multimeter, not my eyes. I'll explain shortly.

You'll be using a variety of components - LEDs, resistors, gator clips, batteries, battery holder, and your multimeter. There's a great tutorial (page 15) on how to read the stripes on resistors - don't skip it. It's titled decoding, and that's exactly you'll be doing - trying to figure out these tiny little colors and convert them to a number.

If you're like me and purchased the fancy blue ones, you'll likely discover just how difficult it is to distinguish some of these colors! Brown and black (on some) look identical... others are hard to tell the difference between orange and red. Later in the book I see the author is going to have you using a helping hand (or 3rd hand) device that usually comes with a magnifying glass; I already have one so it was a huge help. If you've got one (or a simple magnifying glass) keep it in your toolkit - it'll come in handy.

First off, I made a HUGE error when tracking down the 470 ohm resistor; I purchased a big bundle/mix of resistors and thought I had the decoding done properly. Wrong. My trusty multimeter showed me that I didn't have the right resistor... and this little setback also made me realize how fast and easy it is to determine a resistor's value with a multimeter.

That's not to say you shouldn't try and convert using the color/number system... do that first and then use your multimeter to double-check yourself. On a positive note, I was able to find the 1k and 2.2k resistors using just the color codes. I feel good about myself.

So, up next is the experiment that demonstrates how voltage and resistance are inversely proportional... more resistance, less voltage. You really can tell the difference between the 470 ohm, 1k, and 2.2k resistors after you light up that LED... it gets brighter as the resistance drops. (Hard to tell from the pictures, but the LED does change in intensity.)

This was a fun exercise... the gator clips are a little frustrating at times trying to hold those small wires. And, as I mentioned, these dark blue resistors I purchased aren't the easiest to decypher. Keep that in mind as you buy resistors - I think I'll stick with the light tan colored ones in the future.

Okay, that about does it for Exercise 3... here's what you should have taken from your reading and the exercise:

* You can build a simple flashlight (but weak) using a few batteries, a resistor and a single LED.
* Multimeters are good for verifying a resistor's value
* You can blame Andre Marie Ampere if you don't like the Flourine in your water supply
* Resistors are small; when they fall on the floor, you'll never find them again
* There is a method to the color madness of resistors
* Four color stripes are more confusing than three
* It's okay to connect the long LED wire to the negative terminal - it won't hurt but it also won't light up
* A small resistor (in size) doesn't mean a smaller value... that surprised me

Tomorrow, I'll finish up Chapter 1 and cover Exercises 4 and 5.


  1. Man I know why the author wanted to use clips, but its hard getting some of the things together; I think I'll just use a breadboard after this :)

  2. Hi, Matt.

    Yes, the gator clips are a little tricky... but in my batch of 10 or so, there are a few that are really tight and a few that are really loose... I'm going to weed out the loose ones, and that oughta help a bit...

  3. The blue resistors are most likely metalized (versus the beige carbon ones).

    Metalized resistors values are suppose to maintain themselves longer (not go out of tolerance) then carbon.

    Because of that you will also *usually* find metalized resistors in higher tolerance then carbon ones.

  4. Yep, the blue one are definitely more precise in their values - after taking some readings with the multimeter, I was amazed at how close they readings were to the stated value on the package!

  5. I was really worried I'd never be able to get the resistor decoding system, but I did just like you did and use each experiment as practice to identify them. First I would read the value I wanted, then try to figure out the colors by using Black, Brown, ROYGBV (learned that in high school), Gray, White to determine the values and then finally testing my answer with the multimeter. It seems this is one of those cases where practice makes perfect... or at least helps you memorize what the colors stand for.

    It also helped that the pack of resistors I got had 30 of some, 10 of others and 5 of a bunch. It came with a sheet that listed how many of each there was, so that helped narrow down which group each resister was in.

  6. Late to the game here. I'm sorta colorblind (colors, how the heck would I know, I can't tell some of them apart.), so this was an interesting exercise. I found a web site that let you select the colors, then I'd go out in the sun with my magnifying glass and try and pick out the colors, head back into the garage where my workshop is and select the colors on that site, set the range with my multimeter, then correct the colors on the program to get somewhat close to the value the meter told me the resistor was.

    either my resistors are all crap or that meter is off, they were by and large all out of spec by more than 5%. I got the same pack of resistors that brian got I think, if it's from radio shack. I'll try and get some of the blue ones and see.

  7. Had a good time with my boy learning the color-coding system (magnifying glass is really a necessity -- may as well go ahead and pick up that 'helping hand' device with a built-in magnifier at this point) and then sorting them into labeled bins in our electronics toolbox.

    Agree that the alligator clips are a pain to use -- they only clip right on the very end, so if you put two wires next to each other, it'll only grab one of them and the other will slip out. Plus, the insulating cover is VERY slippery. My 9-year-old simply can't clip things together with them. We'll probably use the breadboard going forward.

  8. Most important thing this experiment taught me was that at 44 my eyesight is not as good as it used to be :). I used the multimeter to sort most of my resistor. I got the Components pack 1 from Makershed and found it interesting ;) that about half of the resistors were jumbled up together and the other half we neatly taped together in packs of 10 all with the same value. I think those people over at Makershed wanted to make sure we worked a little :)

    All of the resistors with the Comp Pack 1 had a gold band so they were supposed to be within 5%. They all were. I did find it interesting that they were all low and none of them high. I don't know if there is a reason for that I just found it interesting.

    Definitely a good experiment. I now have a much better understanding of why resistors are needed in circuits.