Sunday, February 7, 2010

Chapter 3 - Exercise 15 Part 5

I am smiling ear to ear today... my confidence in soldering just doubled as I was able to move the circuit from the breadboard to the perfboard, little by little, and get it working. For me, one of the keys I feel to my success so far was getting it working on the breadboard first... troubleshooting various issues - wrong resistors, bad transistor, etc - and testing every step of the way.

Last night I successfully moved over the top half of the circuit to the perfboard. As I mentioned in the last post, I soldered each component and then attempted to test my soldering when possible... I used the multimeter to make sure the resistance values were accurate (use the holes in the perf board, not the resistor leads). I also tested voltage across the capacitors to make sure those were soldered properly, too. I haven't yet found (or heard of) a method for testing the 2N2222 and PUTs once soldered, but maybe someone knows a way?

Today I went and purchased a few extra capacitors of various capacitance but was unable to find the 2.2 microfarad capacitors with both leads on one end (shaped like a barrel) - I could only find non-polarized 2.2s with one lead on each end... argh. So, I decided to substitute a 4.7 microfarad for C1 (just like I did for C3)... took a chance because I didn't know how it would alter the circuit, but I felt it was a reasonable risk given the close values. I got home, soldered in the missing capacitor, and tested the top half of the perfboard consisting of the noise maker - the first video below shows my results.

Next, I started moving over the bottom portion of the circuit - the relay/power section. It had fewer components and was slightly easier to solder because not many of the components are sitting next to one another... the exception being the Diode and R1 and R2. (Note: The R1 and R2 on page 135 is NOT the same R1 and R2 in the circuit on page 91.)

Once again I was a little nervous soldering the 2N2222 because those little leads are so close to one another. And pushing my relay through the perfboard was tricky... the holes were just a little too small and my pushing it felt like I was going to snap the perfboard in half... it did finally go in, but it took a couple of minutes of very careful pushing and widening the holes with a large bore needle.

After the circuit was transplanted to the perfboard, I soldered various strands of wire in place - two green wires that will go to the magnetic switch(es), two black wires (twisted together) that go to the speaker, and a red and black wire (twisted) that will provide power.

My second video shows my testing of the circuit outside of the project box. I used gator clips to hold everything together and crossed my fingers...

All in all, I'm having a blast with this book. The heartbeat LED project (Experiment 14) was fun, but this one is really cementing what I've learned about the way resistors, capacitors, transistors, relays, and diodes are working together. Now I've got to get the project box prepared so I can mount the circuit board and close up the box.


  1. Hey James, I'm guessing that you may have blown the first transistor with excessive current when you used 470-ohm resistors. One thing leads to another!

    I am very excited that you have tackled the alarm project, which I regard as fairly challenging, with numerous opportunities for error. Thanks so much for sharing your process.

    I am also excited that my book is already going into a second edition. This will enable me to correct all the errata that people have reported, so, if you have any more, now's the time.

  2. Charles,

    Yes, the alarm box has been a very fun project... and I'm not even done yet!

    I probably should have guessed that those low value resistors would allow a lot more current through that might damage the transistor... one was damaged, the other not... I b had to switch out both, one at a time, to see if they both were working... just lucked out that I didn't damage more of the circuit, I guess.

    Congrats on the 2nd Edition!! I just wish I was further along - but maybe some of my readers are ahead of me and can speak up if they've encountered any errors from Experiment 16 and up? If you've found some, please submit them to the errata page at: