This past semester, I took Electronics as part of my general courses for my physics major at Hartwick College. The course covers mainly analog electronics with a quick discussion about digital electronics at the end of the semester.
Also at the end of the semester, we are required to build our own circuit. We can follow the design of someone else and our department will provide all the parts needed (which was good, because I went through way too many transistors, a problem I hadn't faced during lab at all during the rest of the semester).
So, from one of the radio shack booklets my professor probably got in 1979, I chose to build a metronome. The circuit seemed kind of easy, and I offered to build something more complicated, but my professor assured me that this circuit was just fine.
Right, not too bad. A PNP transistor, an NPN transistor, a speaker, battery, resistor, capacitor and a potentiometer (or a variable resistor, whichever you prefer).
I set up the circuit as designed, made sure that I had everything connected correctly--base aligned with collector, the wiper of the pot connected with the end terminal, etc. Everything looked fine, to me, so I connected the battery and waited for the "click" of the metronome. When there was no sound, I put the speaker close to my ear in case I was just really quiet (my fellow students were also in lab working on sending a radio signal) and I adjusted the pot in case it wasn't working. I also switched out the resistor for higher values, as per the recommendation of the electronics manual (I believe when I first put the circuit together, I had a 1k instead of 10k in place. I think I kept it at 33k).
I asked my lab partner to check how my board was set up and her quick cursory glance told her that I was fine. I also asked my friend who has aced every single class we've taken in the major, and after a quick correction it should have worked but didn't. I made sure that everything was connected well and found that the second transistor  was HOT, I almost burned my finger. I figured I roasted the transistor, so I switched it out. Still didn't work.
At a loss, I asked my professor for his assistance. After glancing at my notes, he told me that I had the NPN and PNP transistors switched up--a mistake I must have been carrying since we learned about them in class. I have since checked my notes and I realize that my class notes show the correct one. I don't know how I got confused but maybe that explained my marks?Â
I switched the transistors, and when they didn't work, I got fresh ones and was rewarded with a constant "clicking" noise emitted from the speaker.
This picture shows a 1k resistor and probably the wrong transistors. The black and red wires that disappear out of the picture lead to the speaker.
There was nothing as sweet as hearing that clicking sound, two hours after I had begun building the circuit.
I asked my professor if he had a circuit board so I could solder my project. (My grandfather used to work in electronics I believe and he was looking forward to seeing my soldering work.) The next day he gave me a circuit board where the donut holes were completely independent of each other. My first thought was to put all the individual parts in place so I could know that it would work when I soldered them together. However, the solder was going to connect them so that the circuit would work. So I made sure that everything would be connected the right where and where it would be easy to solder the parts together.
However, after three hours working on soldering it together, IÂ still couldn't make it work. I had begun experiencing concussion symptoms and knew that I not only needed to stop, but I also needed to begin working on other schoolwork as finals week was beginning. So I saved everything and have decided I'll return to working on it next time I'm back at school and have time to dedicate to it.
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