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Cole Hoffer - Lab 1

Page history last edited by xinyi xie 9 years, 9 months ago

2. Controlling the Brightness of LEDs

a. What resistance do you need to limit current to 30 mA (if using red LED) or 25 mA (if using yellow or green)? Be sure to state which color LED you are using. This resistance refers to the total resistance in series with the LED.

Using a green LED (25mA)

Forward Voltage Drop = 2.2V

Voltage = 5V - 2.2V = 2.8V

V = IR

R = V/I

R = 2.8 / .025

R = 112 Ohms

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b. Is the resistance from question (a) a maximum or minimum resistance? That is, in which direction if you change the resistance (higher or lower) would the LED likely fail.

It is the minimum resistance. The resistance and current are inversely proportional, meaning if one increases, the other will decrease. Lowering the resistance any more would cause the current to increase above 25mA, causing the LED to fail.

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c. What is the resistance range of the potentiometer?

0 - 10 kOhms +-5%

or .5 kOhms

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3. Basic LED Circuit with Switch

a. Does it matter what order the components of your circuit are arranged between power and ground? Why or why not?

No, all components of the circuit are in series, thus meaning all components will achieve their desired task regardless of their order. If one component is not working properly, the entire circuit will not work because it is in series and the LED will not light. Resistors affect the entire circuit, meaning their placement in the order is not important and the button simply acts as connecting/disconnection in the circuit.

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