Thursday, May 29, 2014

Experiment 1 (Chapter 1) : Glue and Glowing LED

Okay, time to get moving. Experiment 1 ranks up there with Make: Electronics' (Book 1) unusual requests to lick a battery, burn out a battery and fuse, and cut open a relay. This one doesn't even involve a breadboard... just a simple piece of cardboard. 

The setup is simple -- wire up a 2N2222 transistor so it provides current to an LED. There's some important discussion in this chapter on the difference between a 2N2222 and P2N2222 and how the leads are oriented. I also learned a nice mnemonic for NPN transistor identification -- NPN for arrow "Never Points iN." I can remember that.

The other components used in Experiment 1 are a simple 9V battery and harness, a 220 ohm resistor, and some patch cords. I also added in two copper gator clips, but I'll tell you now that they were a bit of a pain because they don't hold two wires together well. Use the tighter clips with the rubberized covers if you have them. (I do have them, but was too lazy to go digging... yet another reason for me to take this weekend and go through all my electronics components and tools and supplies and inventory exactly what I have.) Oh, and you'll need some white glue and two jumper wires to keep the glue off of your clips.

After wiring it up, I touched one of the jumper wires very near the beginning of the glue trail -- near the thicker end. Sure enough, the LED lights up. And just as the text explains, as I moved the jumper wire further from the thicker end of the glue trail, the LED fades and fades until I get nothing. You can watch a video of this first test below.

After testing this "circuit," the text suggest removing the transistor completely to see if you get the same results. If you have a solid understanding of how the purpose of this particular transistor, then you already know what the results will be -- here's another video that shows those results.

For the next video, it's a bit tough to tell but the transistor is reversed... I basically just flipped it over so the CBE leads are now EBC (reading from the top of the cardboard down). The only way to really tell is that the rounded part of the transistor is now facing up (to me) instead of down. Charles explains that using a transistor incorrectly can damage it, and that makes sense. But I had to test it anyway. Here's the results:

My final test for Experiment 1 was to take the "damaged" transistor and put it back in the circuit in its original configuration. As the video shows below, I still get a positive result (LED lights up), but I know I cannot trust this transistor in future circuits.

So, I've tucked this damaged transistor into an envelope (and yes, I know I wrote the label incorrectly -- all those Ps and Ns and 2s get confusing after a while, and yes, I know it's Experiment 2, not 3) and am saving it for the next experiment -- the final paragraph in this chapter suggests using it in Experiment 2 to test its performance against a new transistor... and I plan on doing just that. As you can also see, I have no issues writing in my book and I certainly highlight a LOT of stuff. Not sure what your own plan is for working through the book, but I typically read through a chapter twice... once to get a general feel for the chapter's contents and then a second time where I highlight components I'll need, variations that I should perform, and other important facts that might impact later experiments.
Saving the damaged transistor for Experiment 2.

One little mini-experiment from Chapter 1 that I did not perform was testing the resistance of de-ionized water. I performed a version of this back in Exercise 1 for Book 1, and my understanding of how salt ions increase conductivity in water is pretty good. Feel free to repeat this exercise if you didn't already do it while working through Make: Electronics.


  1. Hello Jim,

    I'm excited to see you embarking on this mission. And surprised you didn't send me the new URL! But I have bookmarked it now.

    The breadboard contacts should not be too tight if you are using the recommended wire. Do you have 24 gauge? 22 gauge will be a fraction too large.

    All of the breadboards that I have used, with just one bus down each side, have two breaks in each bus. You don't need to cut the board open to determine this. Just use your meter to test for continuity. You should find that there is a break between the first three groups of holes, and the next four groups of holes, and the last three groups of holes. There are five holes in each group. Just add jumpers, as shown in any of the photographs of breadboarded circuits in the book.

    You are correct that two capacitors in parallel have a total capacitance that is the sum of their individual values.



    1. Charles, I am SO sorry that I forgot to email you the URL. But very glad to know that you've found it.

      Thanks for the info on the breadboards. I believe the jumper wire I'm using is 24 gauge, but if not I'll start cutting my own. And good to know about the continuity on those boards. Easy enough fix, and definitely glad I won't have to rip one open.

      Hope you had a safe trip home, and it was great meeting you for the first time at Maker Faire.

  2. PS. Thanks for devoting your time to my book. I'm really interested to see how it works out.