Friday, January 8, 2010
Chapter 1 - Exercise 4
So, Exercise 4 has quite a bit of reading... I'm actually going to go back through this once more and make sure I really understand all of this - there's a lot of math and equations, but fortunately it's fairly simple stuff - no Calculus or balancing of chemical equations.
I guess this is as good a time as any to remind my readers that I'm not going to always be going over the reading material or necessarily summarizing it - I'm more interested in documenting the experiment and hands-on stuff. That said, I'll probably still discuss the theory stuff here and there because there is some stuff that I either don't get (right away) or just need to write down to cement it in my head.
So, the first thing I'll share with you here is my taking apart of a potentiometer. Just grabbed a pair of needlenose and pulled up 4 metal tabs. Easy enough. And a closer look under the hood shows me how this thing kind of works... you can see the little "bump" in the metal wire under the rotating knob and how it rubs against the metal ring-thingy... (Sorry to get really complicated and throw a lot of techno-babble at you.)
So, after putting it back together, I rigged up the handful of connections described and starting on page 19. If you missed my earlier post, I was only able to grab a 5k potentiometer instead of the 2k mentioned in the book - this just means I can crank up way more resistance with mine.
After hooking it up to a yellow LED, I got a little bit of light... then rotating the potentiometer's knob clockwise, the LED got brighter. Very cool - less resistance means brighter LED.
I did test this with my multimeter at the two different areas mentioned on page 21 - and you can see in my pictures that my voltage is about 6.4v - add up the voltage measured at the LED and then at the potentiometer and I'm getting a fairly accurate reading. (The author tells you why there's some slight variations in readings... did you catch that?)
Next, I hooked in my multimeter to measure amperage. Even with the gator clips, it can be a bit tricky to connect a wire to a probe. And taking measurements at the two different spots, I got the same value. Not a surprise as that's exactly what I was expecting.
And finally, I took two 1k resistors and measured their resistance in series and parallel (page 25) - this isn't an actual experiment that's shown, but I highly encourage you to do it - see my photos for how I clipped the resistors together (in series and in parallel). As you can see from the two photos, resistance is exactly as expected (2k for series and 500ohms for parallel).
The rest of the pages for Exercise 4 focus on some math, but don't ignore it. We finally learn about wattage, how to read a data sheet (and understand why you can burn out one LED but maybe not another similar looking one), why our tongue didn't burn off back in Experiment 1, and, my favorite, how to do the math to figure out the proper resistor to put into an LED circuit.
I know I said I'd be covering Exercise 5 today, but you'll have to forgive me... a slight dusting of snow today caused schools to be canceled (crazy - we Southerners just don't know how to drive in snow/sleet/ice) and I wasn't able to get to the grocery store while watching my toddler son. Grocery store, you ask? Well, you either don't have the book or haven't peeked ahead to Exercise 5. No worries - I'll try to get Exercise 5 written up and posted by Sunday.