Authorized Online Retailers:



In Lesson 2, we learned how to use browser send control signal to a remote Arduino device and turn On/Off an LED.  In this lesson, we’ll show how to read remote sensor data to your browser. We will use a photoresistor(light sensor) to read remote environment light value. This is very useful in farms, greenhouses to control  the light of plants.

2) Parts and Devices

Arduino UNO 1
Ethernet shield W5100 1
USB cable 1
Photoresistor sensor Module 1
Jumper wires several
Bread board 1

3) Circuit Graph

Connect your Photoresistor with Uno as following diagram

A couple of notes before you get started:

4)Software Installation

Download the sketch file from :

Unzip the download file and enter the folder W5100-lesson3, double click the w5100-lesson3.ino file, upload the sketch to your Arduino. Open your Serial Monitor, you can see your router will assign an IP address to your Arduino   as following:

In above example, is the IP address of my Arduino.
Now use another computer or your cell phone’s  browser to visit url :
In your photoresistor sensor is exposure under light. Your browser will show following result:

Arduino IoT Lesson 3

Real time Photoresistor value: 19, 99% of maximum sensor value

99% means the environment is very bright.

If you use hand to block the photoresistor from light, your will see following result

Arduino IoT Lesson 3

Real time Photoresistor value: 1020, 1% of maximum sensor value.

1% means the environment is very dark.