Friday, January 22, 2010

Chapter 2 - Exercise 11 Step 3

This post covers Step 3 (of 4) for Exercise 11.

I apologize in advance for the somewhat blurry photos - my camera needs to have a nasty accident so I can get a replacement.

Anyway, now we're up to Step 3. I read through it twice... and I think I need to really read over it again to really understand how this combination of PUT and 2N2222 transitor amplifies the speaker. I think I'm understanding it, but I'm going to have to mull it over for a bit longer.

One of the photos here shows the circuit on page 88 - after I plugged it in, I could definitely hear the mosquito pitch coming from the speaker, but I had to put my ear right up to it.

In the remaining photos, I've added to the circuit and it now looks like the one on page 89. Just an FYI - most of the diagrams (like the one on page 88) will tell you the value for any new components added... but Figure 2-109 is missing the value for R9. You can easily look at Figure 2-110 to find it, but just in case you missed it, it's a 2.2K resistor (written 2k2). It is a Red-Red-Orange band resistor.

After adding the second 2N2222 transistor, the speaker was buzzing but it was really about the same level as with the single 2N222 transistor. No real improvement. Let me know if you hear a bigger improvement - maybe I did something wrong.

I really enjoyed Step 3 - if you're paying attention to the schematics (Fig 2-108 and 2-109), you can really start to see how a circuit begins to build on itself... I'm betting from this experience that I'll be better able to tear down a schematic in the future if I take in it small pieces. Take a look back at Figure 2-103 and think about how much you've learned here - what started as a simple schematic has become much more crowded with components... but not really that much more difficult to understand. I'm very pleased to see that I'm getting this... hope you are, too.

Three weeks ago, if someone had handed me the schematic in Figure 2-110 and told me they'd pay me $1000 to build it, I would have lost out on that payment.

Okay, so tomorrow I'll finish up Chapter 2 with Exercise 11 Part 4. And please, those of you following along and doing these exercises (whether you're behind me, with me, or ahead me), let me know how you're doing and your experiences with the book so far.


  1. To minimize blur, I suggest you make sure you're not getting up too close to the object. Basic digital cameras have limitations. Sometimes the screen shows a good shot, but it doesn't come out right. This is, of course, assuming your camera is working electronically and the lens is not dirty.

  2. The blur was my fault... my camera has that close-up feature that I turn on for stuff like this, but a slight movement will blur the image... I should use a tripod but it's such a hassle when I'm in the middle of a project.

  3. I realize I'm a bit late to the party here, but I'm currently running through this experiment myself. Your write-ups have been very valuable this far, and I'll continue to reference them as I go through the book!

    Just wanted to make a quick note here, though. You mention that the 2.2K resistor is red-red-orange, but I believe that would actually be the banding on a 22K resistor. It should be red-red-red, correct?

  4. Hi, Dan.

    Did I say red red orange? I can't remember - need to read back over it and look closely at my images. If it's a mistake, thanks for correcting for future readers.