Electronics Lab

My Lab Partner this week was Laura Ciporen.

With 4 AA batteries before the voltage regulator: 5.48, with regulator: 4.46
With 12V power supply, before regulator: 17.13, with regulator: 5.01
12V, regulator, 220ohms resistor, 1 LED: voltage across the resistor: 3.15, voltage across the LED: 1.79 (when switch is off, all V=0)

• 3LEDs in series: V across resistor: .12, across 1st LED:1.63, across 2nd LED: 1.63, across 3rd:1.62

• 3LEDs in series, no resistor: 1.68, 1.68, 1.67
• Amperage measurements, 2LEDs in series, 220ohm resistor 12v power, power regulator: second LED=4.83mA, 1st LED=4.81mA, resistor=4.84mA

• 3LEDs in parallel: resistor=3.2, all 3 LEDs=1.71

Goofy problem: we were using a push button switch and thought we were using a momentary switch. When we plugged the LED in, it lit up and we were confused but then pushed the switch and it went off so all is right with the world.

Notes to us: We discovered that to measure the resistance of a resistor (or other component) you have to remove it from the circuit (no power connected).
NOTE:When measuring the voltage across components, place the leads of the volt meter on the actual components, not into the board ( yields a more consistent reading).

• We tried adding a 4th LED in series but none lit up.

We think this is because the minimum voltage required to light the red LEDs (the ones we were using) is 1.6 according to Mims.

• Then we tried 3 green ones (min 2.2v) to test our hypothesis about the red ones and they did not light up.
  
• Two green ones did. Confirming our theory.

The starting point for the LEDs to light up varies for LED color: 1.54 for red, 1.74 for yellow & green

Questions:

• If we measure the voltage by putting the leads of the volt meter into the breadboard, what are we measuring?
  
• When we do this and turn off the switch, the voltage across the resistor jumps to 3.64. That makes no sense to us.
• When we were using the pot we were getting readings of 1.54 with the red LED. Then we switched to a yellow LED without touching the pot and got readings of 1.64. Why is that?
  -Different LEDs draw different amounts of current. So the Pot will draw have less Voltage to drop in it's resistor.