PhotoresistorwithAtmel-SanJoseStateUniversity.docVIP

Photoresistor, Transistor, and LED’s Learning Objectives: By the end of this laboratory experiment, the experimenter should be able to: Explain how a photoresistor works Describe the voltage-current relationship for an LED Describe how to capture analog voltage samples with an ADC using the Arduino library Build a circuit that includes an LED, photoresistor, and transistor and interface the circuit to a microcontroller to create a light controlled switch Write a program for the Arduino to control and modify the functionality of a light controlled switch Develop a light-tracking device with Arduino, a servo and photoresistor. Components: Qty. Item 2 10 k? resistor 1 Solderless Breadboard 1 470 ? resistor 1 Photoresistor 1 220 to 270 ? resistor 1 red or green LED 1 Arduino Microcontroller Board and USB Cable 1 hobby servo with attached photoresistor board Introduction: A photoresistor is simply a resistor whose resistance depends on the amount of light that falls upon it. Photoresistors are used to make light-sensitive devices, and are often made from cadmium sulfide (CdS). The resistance of a CdS photoresistor varies inversely to the amount of light incident upon it. In other words, its resistance will be higher at low light levels (in the dark) and lower at high light levels. Two advantage of photoresistors is that they respond to wavelengths of light similar to those of the human eye, and they are very easy to interface to. A disadvantage is that they are a relatively slow-to-respond light sensor compared to other light-detecting devices. A light emitting diode (LED) behaves like an ordinary diode except that when it is forward biased, it emits light. An LED’s forward voltage drop is higher than that of a standard diodes. Typical LEDs (the two-wire leaded “jelly bean” type) require 5 to 15mA to reach full brightness, but are not designed to handle more than about 20 mA of current. You will therefore always need to provide a resistor in series with an LED to li