Lesson 12 – Photo Resistor


  1. Before you start working with any of the tutorials in this series please make sure you have completed the following tasks –
    1. Downloaded and installed the Arduino IDE.
    2. Are able to connect to the Arduino IDE from your computer
    3. Have been successful in uploading a simple (e.g. Blink LED’s) example programs (that comes with the Arduino IDE) onto your Arduino UNO board
  2. If you haven’t installed the Arduino IDE please head back to the first tutorial and make sure you’ve gone through each of the steps involved.
  3. Once you’ve sorted all of the above you are ready to move onto the next tutorial.


After completing all the previous experiments, you may acquire some basic understanding and knowledge about Arduino application. We have introduced digital input and output, analog input and PWM. Now, let’s begin the learning of sensors applications.  Photo resistor (Photovaristor) is a resistor whose resistance varies from the different incident light strength. It’s made based on the photoelectric effect of semiconductor. If the incident light is intense, its resistance reduces; if the incident light is weak, the resistance increases. Photovaristor is commonly applied in the measurement of light, light control and photovoltaic conversion (convert the change of light into the change of electricity).

Photo resistor is also widely applied to various light control circuit, such as light control and adjustment, optical switches, etc.We will start with a relatively simple experiment regarding to photovaristor application.  Photovaristor is an element that will change its resistance as light strength changes. So need to read the analog values. You can refer to the PWM experiment, replacing the potentiometer with photovaristor. When there is change in light strength, it will cause corresponding change on the LED.

Hardware Required – Here’s the hardware you will need for the tutorials :

  1. Arduino Board x1
  2. Photo resistor *1
  3. Red M5 LED *1
  4. 10KΩresistor *1
  5. 220Ωresistor *1
  6. Breadboard *1
  7. Breadboard jumper wire *5

You will find fritzing diagrams below outlining circuit connections for both the Arduino Uno and the Arduino Mega 2560.

Here’s what your project should look like once it’s finished.

Let’s have a look at the code for the tutorial.

int potpin=0;// initialize analog pin 0, connected with photovaristor
int ledpin=11;// initialize digital pin 11, output regulating the brightness of LED
int val=0;// initialize variable va
void setup()
pinMode(ledpin,OUTPUT);// set digital pin 11 as “output”
Serial.begin(9600);// set baud rate at “9600”
void loop()
val=analogRead(potpin);// read the analog value of the sensor and assign it to val
Serial.println(val);// display the value of val
analogWrite(ledpin,val/4);// turn on the LED and set up brightness(maximum output value 255)
delay(10);// wait for 0.01

After downloading the program, you can change the light strength around the photovaristor and see corresponding brightness change of the LED.  Photovaristors has various applications in our everyday life. You can make other interesting interactive projects based on this one.


This development track requires an investment a bit of hardware. See below for details –

  1. Arduino IDE –
    1. You will need to download and install the Arduino development IDE.
    2. The approach to installation, configuration, setup of the Arduino IDE is covered in our tutorials.
  2. Arduino Uno, Sensors, etc. –
    1. You will need to purchase the Super Learning Kit for Arduino from OzToyLib.
    2. The Arduino Advent kit has all the sensors you need to perform the tutorials covered in this development track.
    3. If you do not have an Arduino Uno or Arduino Mega 2560 you might want to head over to Arduino boards and pick one up now.

The Super Learning Kit for the Arduino kit has all the sensors you need to perform the tutorials covered in this development track.

About the Super Learning Kit for Arduino

The Super Learning Starter Kit for Arduino comes packed with ~35+ different electronic bits (Sensors, LEDs, switches, LCD, servo, etc.) and can be purchased with either the Keyestudio UNO R3 or the Keyestudio Mega 2560 board. The Keyestudio Arduino boards can be used to interface with the different electronic bits i.e. sensors, LED’s, switches, servos, etc. included in the starter kit. The starter kit for the Keyestudio Uno R3 offers a great opportunity to explore the world of electronics using the Arduino Development Platform. Interact with the real world through the various sensors, create innovative projects, learn how to program the micro:bit to read data from the sensors and perform certain actions. The starter kit for the Arduino is a great way to dive into the awesome world of electronics and get started with your own STEM (Science, Technology, Engineering, Math) learning journey.

The Arduino advanced study kit walks you through the basics of using the Arduino in a hands-on way. You’ll learn the fundamentals of electronics and working on the Arduino through building several creative projects. The kit includes a selection of the most common and useful electronic components with a book of 32 projects. Starting the basics of electronics, to more complex projects, the kit will get you interacting with the physical world using sensor and actuators. Along with the kit you get access to detailed tutorials and wiring diagrams.

You can purchase the Super Learning Kit for Arduino from OzToyLib.

About the Arduino UNO

The Arduino UNO is the most used and documented board of the whole Arduino family and very easy to setup, play with. The Arduino UNO is a microcontroller board based on the ATmega328 . The Arduino UNO has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz ceramic resonator, a USB connection, a power jack, an ICSP header, and a reset button. Here’s a listing of the some of the features of the Arduino UNO –

  1. Microcontroller: ATmega328
  2. Operating Voltage: 5V
  3. Input Voltage (recommended): 7-12V
  4. Input Voltage (limits): 6-20V
  5. Digital I/O Pins: 14 (of which 6 provide PWM output)
  6. Analog Input Pins: 6
  7. DC Current per I/O Pin: 40 mA
  8. DC Current for 3.3V Pin: 50 mA
  9. Flash Memory: 32 KB of which 0.5 KB used by bootloader
  10. SRAM: 2 KB (ATmega328)
  11. EEPROM: 1 KB (ATmega328)
  12. Clock Speed: 16 MHz

Arduino is an open-source, prototyping platform and its simplicity makes it ideal for hobbyists to use as well as professionals. The Arduino UNO contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started. The Arduino UNO differs from all preceding boards in that it does not use the FTDI USB-to-serial driver chip. Instead, it features the Atmega8U2 microcontroller chip programmed as a USB-to-serial converter. “Uno” means one in Italian and is named to mark the upcoming release of Arduino 1.0. The Arduino Uno and version 1.0 will be the reference versions of Arduno, moving forward. The Uno is the latest in a series of USB Arduino boards, and the reference model for the Arduino platform.

You can read more about the Arduino here – www.arduino.cc.