PhysComp lab, week 3: Electronics

This week’s PhysComp lab looked pretty straightforward, but that’s only if you don’t take into account my singular gift for turning LEDs backward and mixing up power and ground on the breadboard.*

So, first, there was the obligatory soldering. It wasn’t quite so bad this time, I think, though I did manage to melt some of the plastic inside the jack.

Soldering the DC power jack

Then I had a lot of puzzlement over the high voltage readings I was getting. And there was a burning smell, even though I’d turned off the soldering iron ten minutes before. Hmm. Could there be something wrong with the—

Ice used after I made the mistake of touching the voltage regulator

Handy Tip: Voltage regulators get really fucking hot. Don’t touch them.

Finally, I found the wire that was going into ground instead of power and got the desired voltage reading. Then, I added a switch and an LED.

Breadboard with power jack, voltage regulator, push-button switch, and LED

And, again, wired the switch into ground instead of power. Got that sorted, and—

Pressing the switch to light the LED

Ta da!

The next step, putting two LEDs in series, went fine (with voltage readings of 2.11 for the red LED and 2.88 for the green), but when the instructions said to add a third . . . well, I’m not sure how you add a third LED in series. Is it like this—

How do you put three LEDs in series?

Probably not, since that wiring scheme works, while the instructions imply that adding a third LED makes them all go out. Comparing my voltage numbers here would probably tell me the answer to this question, but although I took lots of photos to record the multimeter readings, I can’t remember which reading was from which part of the circuit or taken at which step. Sigh. I should have just written them down.

Setting the LEDs in parallel was also pretty easy, but measuring the amperage across them was simply not happening. I tried it every which way, but I couldn’t get the circuit closed with the multimeter as part of it. After trying several interpretations of the written instructions and circuit diagram, I gave up and moved on to the pot part.

Breadboard with potentiometer and LED

Again, no problem wiring it. The voltage readings were 1.78 at about halfway and 2.89 at full blast.

This lab took me about four hours, sadly.

* The reason for the latter, in my defense, is that the breadboard in my kit has ground on the outside rows, while the breadboard in all the photos within the instructions has power on the outside. I always forget to check the color of the row, matching only the position. And sometimes I’m just not paying attention.

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