Development of Wireless Control Electrical System Using GSM Technology


GSM Based Home Automation System


It is basically known that any electrical appliance is controlled with a switch that regulates the electricity to electrical devices. As a reason of the latest technological advances, automation and wireless control of devices has becoming more popular.

This project puts forth the equipment which enables users to control their home appliances using their cellular phone. It shows the construction and working of the device to wirelessly control the home appliances based on GSM networking and 8051 microcontroller.

Initially an authenticated signal is sent from the user’s cellular phone via Global System for Mobile Communication (GSM) network to the phone which is fixed to the equipment. This signal or code consists of the information about the function or action to be taken place i.e. what appliance should be turned off or turned on.

The receiver phone receives the DTMF signal or a SMS message that is send from the user’s phone and then sends it to the DTMF decoder or the GSM modem which in turn sends the output digital signal to the microcontroller.

Then the microcontroller, based on the received signal, controls the different relays connected through ULN2003 (Darlington transistor) and triggers the required appliance.

Key words: GSM communication, Wireless Control, SMS, DTMF


As a reason of drastic developments in the field of wireless communications these days, the applications of this technology can be used in various sectors for making daily tasks comfortable and easy.

One such application can be used for control of electrical appliances which results in effective and efficient use of electrical power reducing the loss. This area has yet to be explored in major parts of the world. So we would like to take this opportunity to put forward a cost effective method for the wireless switching of the electrical appliances.


 The main aim of the design provided in this project is to develop a device to have wireless control of home electrical appliances. The device can be made sure to be available at a low cost so that everyone can afford it. This is basically a device built for home appliances control system that can provide remote access to house hold electrical appliances at low cost and in efficient way.

The electrical devices connected in the home, office or any place, consume electrical power, and there is an absolute necessity of saving of power as per present day situations. So it is necessary to control electrical devices more effectively and efficiently at anytime from anywhere. So this project is built for the sole purpose of efficient control of electrical appliances.

This project is basically built on the process of wireless communication through the GSM network. GSM plays a very important role in the present day life of a person. Each and every person now-a-days has a cell phone with him, and GSM network makes the people across the world to communicate with each other.

So as technology is increasing so vastly now-a-days, everything in the world is being automated and wireless for the comfort of man. So here we are building a device based on the GSM network to control the electrical appliances through a cellular phone.

Here we are going to design a cell phone based remote control of electrical appliances. This system is designed for controlling arbitrary devices according to the necessity. It includes a cell phone which is connected to the designed system.

Basically for the system to work a phone call is made to the designated number or a message is being sent containing a password. As the caller press the specific password, it results in turning ON/OFF of the particular device. The switching of devices is achieved by relays.



The block diagram of our project is shown below in the fig3.1.0. It is an outline description of how we have implemented our project and the various steps involved in it.

From the block diagram given below, the first mobile station is used as a transmitting section from which the user sends a code that contains commands and instructions to the second mobile station which is based on a specific area where our control system is located, through GSM network.

The received code can be in either DTMF format which is send to the DTMF decoder connected via headset jack of the phone or through an SMS. 

The DTMF decoder converts it into digital signal and sends it to the microcontroller interfaced to it. Then the microcontroller processes the code and carries out the specific operations. The ULN2003 is used to drive the relay circuits which switches the different appliances connected to the interface.

After connecting the circuit properly and assuming all the connections are right the following steps are to be followed:

  • The remote user send authenticated signal including commands to the receiver phone.
  • Through the GSM network the signal is received by the receiver phone on the device.
  • Then that DTMF signal is passed to the DTMF decoder to convert it to the digital signal, and it sends them to microcontroller.
  • Microcontroller issues commands to the appliances and the devices connected will switch ON/OFF.

And  if we are using GSM module, that is SMS mode, the signal send in the form of SMS is send to the GSM module and then to microcontroller through serial communication and then microcontroller command the relays to switch the devices.

                                                      BLOCK DIAGRAM

Block Diagram


Table 1   Equipment Required Equipment Device Quantity
1 8051 microcontroller IC AT89S52 1
2 DTMF decoder MT8870 1
3 Crystal Oscillator 3.579545 MHz 1
4 Crystal Oscillator 11.0592 MHz 1
5 Relays SPDT 3
6 Transistor ( Switching ) ULN2003 1
7 LED’s 4
8 Voltage Regulators NJM7805 2
9 Transformer 1
10 Bridge Rectifier 1
11 Capacitors As Req
12 Resistors As Req
13  GSM module SIM300 1

In addition to these a cellular phone is required which has to be connected to the device to receive the code from the user’s phone. The resistors and capacitors are to be selected according to the ratings of these equipment selected and also for the efficient performance of  the device.

The software required for the programming of the 8051 microcontroller is Keil µ Vision, in which we program the microcontroller to do the required work as desired, and finally all the basic things like the breadboard, input pins, sockets, soldering gun etc.


Program Description

In programming some string are defined for comparing.


String TV_ON=”TV ON”;

String TV_OFF=”TV OFF”;

String LIGHT1_ON=”light 1 ON”;

String LIGHT1_OFF=”light 1 OFF”;

String LIGHT2_ON=”light 2 ON”;

String LIGHT2_OFF=”light 2 OFF”;

Working & Components Used


Working of this project is very simple. when we sends any message to system’s GSM module, this message is store in an array namely STR and then program extracts the mobile number and main message from it by using some programming methods.

Mobile number is store in a string namely string number and main message which is kept in * and # is store in a string namely string name.

After this process by using string matching function we match name string with defined strings and if match occurs, related function is performed and GSM sends back a related notification message to sender’s number, besides this LCD also displays the notification message but in my own project there is no lCD display.


If in number string stored value after extracting is “0806xxxxx”

And in TV ON string is match with name string then TV will turn ON and GSM sends back a notification message like TV ON.

And likewise for another appliances

Video on how the system Work

For more information Contact Us

Alex Raji


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