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Important note:
Note about using batteries or home-based power supplies:

Also, consider using discarded AC/DC adapters. Just cut-off the end connector and wire with banana plugs or alternatives.

Lab work modification:

1- All Parts and Steps: If you cannot measure a current, it is fine. If it involves the current with a LED, and a current change is required, just show pictures, or state your observation of the LED variation in brightness as evidence of the current change.

2- For Part B-Step 4: Question 2: it is OK to do modification as shown below:

    -2.a    If you have high efficiency LED that is very bright with low current (few mA), you can use the load series resistance in the range of kOhm, not 100's Ohm. Example, for the blue and yellow ones below, each has a 10-kOhm and 1-kOhm resistor, respectively, because they would blind the webcam with higher current (although not the cell phone cam below). At home, you can use whichever value so that a LED brightness is acceptable to your eye, usually in the range from few mA - 20 mA (or even more if for the typical red and green LED). It also depends on the camera you use to take picture and paste in the report. The exact resistor value is not important, especially if you cannot measure the current anyway; just report the resistance value you use.

    -2.b    If you know how to use a potentiometer (go to Lab 2, Part B for a description how to use it), instead of pulling the series resistor out and replacing it with different resistors of increasing resistance, you can just tune the pot from 0 to 10 kOhm, which should be in series with another resistor as shown in the right-hand-side schematic (1 kOhm in the picture). Just demonstrate that the LED is dimmer if you increase the potentiometer resistance.

3- For Part C-Step 3: You can build a circuit that combines both serial and parallel LEDs as shown below and will be accepted as both circuits (IOW, one is counted as two). If you build two separate circuits with more than 5 LEDs in each, you will get extra credits. (however, 10 V will be enough only for 5 LEDs in series. For parallel, of course, one can have practically as many LEDs as one can afford as the AD2 can give ~700 mA).



 

More serial & parallel: 15 V can drive at most 6 serial LEDs of mixed color with a little margin, and barely with 7. See below

Yellow and green are barely visible.

Without the red and white on the left, the pink and orange (right most) are actually bright, but not obvious with strong camera flash. Below are without flash. The right most LEDs are actually orange to the eye, not reddish.

Attenuated with another neutral density filter, the right most are orange, not red.

21.5 Volt can drive 9 mixed color LEDs with high brightness. It can do 10 with lower band gap LEDs (red, orange)

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