Thursday, August 28, 2014

Experiment 13 Part 2 (Chapter 13) -- Making Mistakes

I'm going to wrap up Chapter 13 with a couple of videos and some photos. Unfortunately, one of the videos you might be expecting is NOT here. I synched my phone and downloaded photos and videos, but the video for the circuit shown in Figure 13-7 (page 96) has disappeared. Poof. It's frustrating because although it wasn't a tricky circuit to wire up, it did take some time. My wiring wasn't as pretty as Charles' (no big surprise), but the circuit did work -- a suitable level of volume (tapping on the electret) got the 555 timer chip started and the 3" loudspeaker to making an awful noise. It would definitely make someone stop talking loud, but I'd probably prefer a higher voice volume than the pitch coming out of that speaker.

Where are you, video!??
Here's a photo of the missing video's circuit. I didn't vary much from Charles' diagram with but a few exceptions -- instead of the 33K (near the bottom of the schematic) I used a 47K... no 33K in my batch and I didn't feel it would be detrimental to the circuit to avoid putting two 15Ks in series. Also, I didn't have a 0.068microfarad capacitor, so I substituted a 0.1microfarad. Again, the circuit worked, so these substitutions didn't seem to have a negative effect.

You can't see the speaker, but you can see the two wires exiting the bottom of the breadboard... it's about a three foot length of wire. Lots of popping and static, but it worked.

Note to self: Find a small baggie of mixed capacitors in all values and buy it! I have a good assortment, but I continue to find values I don't have in my capacitor collection.

After completing the larger circuit, I went back a few pages to a small experiment Charles described that uses two 2N2222 transistors and a handful of 1K and 10K resistors. Depending on the wiring of these resistors, you'll gain a better understanding of the subject of Emitter Follower that Charles introduces on page 94. Voltage at the Emitter (E) is directly related to the voltage at the Base (B). It took me a few reads and then performing the experiment with a meter to grasp what was happening, but it does follow the most basic understanding of a 2N2222... and it pulls in the concept of voltage division once again. Very cool!

Note: You can perform these experiments with a single 2N2222 but it goes faster if you have a pair. Even better, if you have four 2N2222s, wire them up following Figures 13-5 and 13-6 and knock all four tests out on one breadboard.

The chapter does round out with a discussion on some of the problems that Charles encountered with his circuit. I was providing a solid 9V using an AC Adapter with a selector for voltage... whereas it appears that Charles was using a 9V battery more often. Some of the technical issues he encountered seem to be related to that fact. If you're using a 9V battery, definitely read some of the suggestions (on page 98) for fixing the circuit if you're having issues with it.

Up next? Experiment 14! Videos below... Part 1 at top, Part 2 on bottom.

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