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Lab 2: Electronics

May 22, 2009

Same night as Lab 1, so the Kitchen’s still a mess.  I got out the LEDs and switches:

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I think I figured I’d done all the voltage measuring last go-round, so I’d plunge right into the fun stuff.  LED’s.

I mentioned before that for all my shopping I’d forgotten the most basic item.  Wire.  I didn’t feel like cannibalizing anymore battery connectors, and the braided wire is a pain to work with.  I broke a bunch of headers apart into single posts and used them to mount alligator clips.  Once reduced to a single pin, the black plastic slides up and down on the header like a bead, so there’s not much more to it anymore than a simple staple, but it does the trick.  Keep in mind in the following photos that I respected the red and white for power leads, and black for ground.

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For some reason I couldn’t get it to work.  I checked the voltage between every component, and all seemed fine, except at the switch, so I concluded it was defective, and basically treated the alligator clip as a switch:

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Later I realized that there was nothing wrong with the switch.  I just didn’t get it.  It’s always off, unless depressed–it’s not a toggle.  

The LED, too, brings its own mysteries.  I knew it has a direction, like a funnel, and that the long and short legs are polarized, but wasn’t sure which was which.  Physical Computing notes that the “shorter leg is the cathode (-), and the longer leg is the anode (+).”  From this one might infer that the long leg goes at the “front” of the circuit, like a battery, but this is not the case.  In a diode, the current flows from the negative pole: http://en.wikipedia.org/wiki/Cathode.  This certainly begs more study.

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Components in Series:

This one is fun but pretty straightforward.  Two LEDs in the series in place of one.  Note that the resistor is by-passed by feeding the two LEDs off the bus so that they get sufficient voltage (2.66V and 2.38V respectively on a 5.05v circuit).

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Here it is with 3 LEDs, clearly not enough voltage (1.71V, 1.62V and 1.71v respectively in a 5.05v circuit):

 

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Components in Parallel; Measuring Amperage:

I plunged right into this one and got a good lesson in the difference between parallel and serial circuits.  Note the absence of a resistor.  Its there on the breadboard, but not in the circuit.  This is how the lab photo and schematic depict it, but they don’t depict the aroma of the burning LED.  Everyone of those LEDs was cooking along a4.57v, not divvying up the voltage.IMG_0395

I inserted the resistor back into the circuit and things calmed down to 1.9V.  The LEDs were drawing 14 mA apiece, 45 mA without the resistor:

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I tried one more sadistic experiment, disconnecting all the alligator leads and checking the amperage between the positive and negative bus posts.  I got a constantly descending amperage on the busboard with a distinct burning smell of a very hot voltage regulator.  Assuming voltage to be more or less constant at 5V, and amperage decreasing, it makes sense that resistance was increasing and being dissipated by heat.  For the time being anyway: put another way, if the regulator is heating up and about to catch on fire, it makes sense that its resistance might be changing–in this case going up–and therefore the amperage going down.

 

And for a finale, the potentiometer:

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Goodnight.

 

 

 

 

 

 

 

 

 

 

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2 Comments
  1. Shawn permalink

    Did you get a nice feeling with the pot in there? I love the feeling of total control over electricity that pots give me..

    • mfleisig permalink

      Very nice, but not as nice as getting an LED to go blink blink! Next post is for you, amigo.

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