Monday, June 23, 2014

Experiment 2 Revisited

Camp ended on Friday -- 21 campers went home happy with a fully-functional Arduino-powered robot. I'll post some photos and thoughts on the camp in another post, but today... back to Make: More Electronics!

Back in Chapter 2, Charles shows how he connected up two analog gauges to record milliamps and microamps, and that's exactly what I've done. Look carefully on the back of the gauges and you'll see one of the two posts (hopefully) labeled with a negative (-) sign. If not, take your best guess, but start with low amperage flowing through the gauges so you don't potentially damage one or both (because they CAN go in both directions, and I don't know if wiring them incorrectly could make the needle swing counter-clockwise and damage the spring inside).

I recorded values just as with Experiment 2, recording micro and milliamp values as well as taking voltage readings between the Emitter and Ground. I've got a video below showing the basic setup.

After finishing up with a "good" 2N2222 transistor, I substituted in the "bad" 2N2222 and performed a similar set of readings. These were "identical" 2N2222, meaning they have the same designation and came from the same order batch... but as with anything manufactured, there are certainly going to be variations in the quality and such. That said, I was quite surprised to find that my readings for the bad 2N2222 weren't that far off from the "good" transistor readings.

Now, I'm using analog gauges, so I'm looking at the small tic marks on the face of each gauge and making a judgment call -- is the needle closer to 1.0 or 1.25? There's an accuracy issue here, not just with the bad 2N2222 but also with my visual reading of the gauges. All other components being equal, there's still a lot of unknowns in this experiment, so I can't 100% declare that the bad 2N2222 was really damaged by reversing its insertion into the breadboard in an earlier experiment.

If the good and bad transistors are supposed to provide values within a +/- 5%, then I could look at the data and say YES... damaged transistor. I think one of the takeaways here is that when building a circuit, if you know you're supposed to be getting a certain amperage from a transistor OR a specific amount of voltage, then Experiment 2 definitely shows us how to setup a quick and easy test to measure a transistor's input and output.

I may not know if the "bad" transistor can be used in future circuits or not, but for such an inexpensive component, I tossed it rather than take chances. Again, if you leave this lesson understanding how the circuit works, and how to obtain voltage and current readings into and out of a transistor, give yourself a pat on the back -- lesson learned!

Tomorrow... on to Experiment 4. Here's the video for Experiment 2 Revisted:

Note: You may have noticed in the photos that I'm using a different style of breadboard. I'm not giving up on these new breadboards I ordered, but they sure aren't as easy to insert jumper wire. This particular breadboard was the one I used while working through most of the experiments from Make: Electronics -- you can't see it, but I have a small foot pedal on the floor that lets me turn on and off a 5-12DC power source that provides the power. I always liked that setup and I brought it out again -- it also helped that the 5V regulated circuit was still wired into the top of the breadboard and ready to go!

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