Intro to Physical Computing - Lab 1

Part 1: Measuring Voltage

The first goal of this lab, was to get power to the breadboard, wire it properly for power, and measure the resulting voltage. So here is the wired board: This board was connected to the 5V and GND pins on the Arduino, in the Red and Blue lanes, respectively. And the measured voltage that resulted: My meter is auto-ranging, so I didn't have to set anything special to get it to output at the proper order of magnitude. I also wired the board so that the opposite side could receive power. Part 2: The Basic LED Circuit Then I built my Basic LED circuit. Without the resistor in place, the LED soon gets too bright, then burns out. With a 220 Ohm resistor in place, the LED glows at a reasonable brightness, and can last a long time. I also put a momentary pushbutton switch into the circuit to control it. The voltage I measured across the LED when the pushbutton switch was engaged was 2.097v. Across the 220Ohm resistor, the voltage was 2.508v. Seen here in both ON and OFF positions! I used the following chart to find out which resistor was 220 ohms. (Source 3) And the wikipedia page on LED's is incredibly helpful as to which end is which: (source 2) Part 3: Components In Series Here I connected two LED's, one after another, in series. The voltage across each, was 2.403v across red, and 2.475v across yellow (not pictured, done for measurements). Together they added to 4.878, which is really close to 4.91, but as the lab said, there's always some loss. For curiosity's sake, I used my voltmeter to test the resistance of each diode. Miraculously, each was around 220 Ohms! Each LED has a 220 Ohm resistor in the circuit (in this case another LED) keeping it from burning too brightly. Part 4: Components in Parallel, Measuring Amperage Then I connected 3 LEDs in Parallel The amperage across each in this configuration was 0.67mA. Each of these were brighter (and hotter!) than they should be, so I thought I'd look up the formula on parallel resistance to see what the correlation here was. (Source 4) Apparently, in series, resistance stacks like so: Rtotal = R1 + R2 + R3 + R4(...) . But in parallel resistance stacks like so: Rtotal = 1/(1/R1 + 1/R2 + 1/R3 + 1/R4...) So the total resistance (before/after the LED) for any of those LEDs was 1/(1/220 + 1/220) OR only 110 Ohms. The Total resistance for the circuit by that formula was 73 Ohms. Part 5: Generating a Variable Voltage with a Potentiometer The voltage across when the potentiometer was approximately in the center position was 2.803v, across the resistor was 132mV, and across the LED was 1.842v. Sources: 1. http://itp.nyu.edu/physcomp/Labs/Electronics 2. http://en.wikipedia.org/wiki/LED 3. http://n1ofz.connares.org/resources/resistor_code.gif 4. http://www.outlawnet.com/~oclass/electricity/formulas.htm#parallel