Data Sheet

UCTRONICS Ultimate Starter Leaning Kit for Raspberry Pi #K0064
102 www.uctronics.com
8.17 Project 17: Photoresistor
8.17.1 Overview
In this lesson, we will learn how to measure the light intensity by photoresistor and make the
measurement result displayed in the screen.
8.17.2 Requirement
 Raspberry Pi ×1
 ADC0832 ×1
 Photoresistor ×1
 10KΩ Resistor ×1
 Breadboard ×1
 Several Jumper wires
8.17.3 Principle
1. What
’
s Photoresistor ?
Please refer to chapter 3.24 Light Sensor (Photoresistor)
2. Working Principle
A photoresistor is made of a high resistance semiconductor. In the dark, a photoresistor can
have a resistance as high as a few megohms (MΩ ), while in the light, a photoresistor can
have a resistance as low as a few hundred ohms. If incident light on a photoresistor exceeds
a certain frequency, photons absorbed by the semiconductor give bound electrons enough
energy to jump into the conduction band. The resulting free electrons (and their hole
partners) conduct electricity, thereby lowering resistance. The resistance range and sensitivity
of a photoresistor can substantially differ among dissimilar devices. Moreover, unique
photoresistors may react substantially differently to photons within certain wavelength
bands.
The schematic diagram of this experiment is shown below: