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Relay is a useful electronics switch which can be controlled by low voltage signal. Relay is often used by computer to control high voltage circuit.

In this lesson, we will show you how to  to turn on/off Relay and Buzzer from a remote browser through internet  .

We  will  use  Osoyoo Mega-IoT Shield  to connect Relay, LED and MEGA2560 MCU board.  Arduino MEGA2560 board can work as a web server. Remote browser can access this web server and control the Relay connected to D13 pin of MEGA2560.

OSOYOO MEGA2560 Board x 1
OSOYOO MEGA-IoT extension board x 1
USB Cable x 1
Relay module x 1
Buzzer module x 1
PnP cable x 1
male to female Jumper x 3
male to male Jumper x 1

First, please plug OSOYOO MEGA-IoT Extension Board into MEGA2560 board:

Then connect as below (Jumper Cap should connect ESP8266 RX with A8, TX with A9):

Relay – OSOYOO MEGA-IoT Extension Board:
Relay Module – D6
COM – 5V (Jumper)

Buzzer Module – OSOYOO MEGA-IoT Extension Board
VCC – 5V (Jumper)
GND – GND (Jumper)

Relay – Buzzer Module
No – SIG (Jumper)

Notice: Shut off your battery or Unplug your power adapter when upload sketch code to Arduino.

Step 1 Install latest Arduino IDE (If you have Arduino IDE version after 1.1.16, please skip this step)
Download Arduino IDE from?, then install the software.

Step 2 WifiEsp Library Installation (if you have installed WifiESP library, please skip this step)

OSOYOO MEGA-IoT extension TX/RX pin to Arduino A9/A8 pin by default. So in Arduino sketch code, we need use Software Serial Port to communicate with ESP8266 (set A9 as TX and A8 as RX in softwareserial object).

To use this wifi shield in Arduino IDE, we need download?WiFiEsp-master library from following link:

Open Arduino Sketch – Include Library- Add .Zip library to load above zip files into Arduino IDE.

Step 3 After installing above library, please download the main code from following link, unzip it, you will see a folder called “smarthome-lesson15”:

Step 4 After above operations are completed, connect OSOYOO MEGA2560 Board to PC with USB cable.

Step 5 Arduino IDE:Choose corresponding board type and port type for you project.

Step 6 Arduino IDE:  Click file – Open, then choose code “smarthome-lesson15.ino” in the folder, load up the  sketch onto your Arduino.

Note: In the  sketch, find   following lines:

char ssid[] = "******"; // your network SSID (name)
char pass[] = "******"; // your network password

please replace the ****** with your correct wifi SSID and password, otherwise your project can not connect to Internet.


After loading the sketch to Arduino , open the serial monitor in the upper-right corner of Arduino IDE, you will see following result:

From the serial monitor ,  you can see the IP address of your MEGA2560 board in the read circle (in above picture, use your browser to visit the website http://mega2560-ip-address (in above case,, you will see following result:

click the two links as showed in above picture, you will turn on/off the Relay module which is connected to your MEGA2560 through the IoT Shield. If Relay is turned on, you will hear buzzer alarm, if relay is off, buzzer will also be turned off.