Android and Arduino SMS Based Home Automation





Introduction: Android and Arduino SMS Based Home Automation

Recently, I received a relatively cheap Quad Band GSM/GPRS module to play with. It is a SIM800L module, and communicates with any micro via a serial port. It came complete with a panel mount antenna.

I decided to build a simple SMS Controller system which uses short message service (SMS) commands to control devices and indicate alarms.

Step 1: SMS Commands

AS with any communication system, specific commands need to be send to a remote device to tell it what to do. Likewise, the remote device needs to reply or react on these commands. This project consists of two parts, the SMS Controller, and an standard cellular phone.

The idea was to create a simple SMS Controller with four digital outputs. Depending on the received SMS, the unit must be able to control the individual outputs.

I also decided to include four digital inputs. This can be used to indicate alarms or other information.

Before starting the build, I decided to create specific commands for specific functions. This 'commands' will be sent using an SMS from a cellular phone.

SMS Controller Receive Commands:

o1:1 - turn output 1 On

o1:0 - turn output 1 Off

o1:p - pulse output 1 On, then turn Off

o2:1 - turn output 2 On

o2:0 - turn output 2 Off

o2:p - pulse output 2 On, then turn Off

o3:1 - turn output 3 On

o3:0 - turn output 3 Off

o3:p - pulse output 3 On, then turn Off

o4:1 - turn output 4 On

o4:0 - turn output 4 Off

o4:p - pulse output 4 On, then turn Off

???? - Request status of Inputs and Outputs

#### - Reset system

For feedback, the SMS Controller should respond to the received commands, and reply with an SMS. I decided that this reply SMS should include the status of all I/O pins.

SMS Controller Response Commands:

i1:x i2:x i3:x i4:x o1:x o2:x o3:x o4:x

where x is the I/O status, 1 for On, 0 for Off.

Step 2: Building the SMS Controller

Equipment required:

Any Arduino, or stand-alone ATMEGA328p on a breadboard

SIM800L GSM/GPRS Module with a sim card capable of sending and receiving SMS's

Step down DC/DC converter

NOTE !!!

The DC/DC converter is required to power the SIM800L module. This module operates between 3.7V and 5V, depending on the version you have. This module also requires a power supply that can deliver up to 2A when the module transmit data. It can not be powered directly from the Arduino Uno !!!

The circuit is quite simple. I have assembled and tested it on breadboard.

The power to the circuit is via the DC/DC converter, with the output voltage set to 4.5V. There are four LEDs to simulate the digital outputs, and four buttons for the digital inputs. The SIM800L is connected to the Rx/Tx pins of the ATMEGA328p.

A 5th LED is used to indicate when the system in busy sending an SMS.

Step 3: Programming the ATMEGA328p

Before programming, open the INO file, and edit the phone number. Replace xxxxxxxxxx with your own cellular phone number in line 46. Recompile, and upload the file.

Also, read the instructions on how to configure the Software Serial port in the INO file.


// ! ! ! NOTE ! ! !

// ================




// To use Software Serial, the user should also change the Software Serial BUFFER to 200.

// This must be edited in the following file:


// C:/Program Files/Arduino x.x.x/Hardware/Arduino/AVR/Libraries/SoftwareSerial/src/SoftWareSerial.h


// Change buffer as below:


// #ifndef _SS_MAX_RX_BUFF

// #define _SS_MAX_RX_BUFF 200

// RX buffer size

// #endif



Refer to this instructable to program the ATMEGA328p on the breadboard using an Arduino UNO.

Step 4: Using the SMS Controller

Using the SMS Controller

The SMS Controller will automatically send an SMS to your phone if any of the four inputs are triggered. The details of the trigger will be contained in the SMS text.

The SMS messages and commands can be edited to your needs in the INO file.

Testing the SMS Controller Outputs

From your cellular phone, send the following commands to your SIM800L simcard number:

o1:1, this will turn on output 1.

On your phone, you will receive the following SMS:

i1:0 i2:0 i3:0 i4:0 o1:1 o2:0 03:0 o4:0

01:0, this will turn off output 1.

On your phone, you will receive the following SMS:

i1:0 i2:0 i3:0 i4:0 o1:0 o2:0 03:0 o4:0

01:p, this will turn on output 1 for 1 second, then turn output 1 off again (pulsed).

On your phone, you will receive the following SMS:

i1:0 i2:0 i3:0 i4:0 o1:0 o2:0 03:0 o4:0

Testing the SMS Controller Inputs

On the SMS Controller, press button 1 briefly

On your phone, you will automatically receive the following SMS:

i1:1 i2:0 i3:0 i4:0 o1:0 o2:0 03:0 o4:0

On the SMS Controller, press button 2 briefly

On your phone, you will automatically receive the following SMS:

i1:1 i2:1 i3:0 i4:0 o1:0 o2:0 03:0 o4:0

On the SMS Controller, press button 3 briefly

On your phone, you will automatically receive the following SMS:

i1:1 i2:1i3:1 i4:0 o1:0 o2:0 03:0 o4:0

As can be seen on the received SMS, the outputs changes according to the commands received. However, the inputs does not change back from a 1 to a 0 after the buttons were pressed. Because I wanted to be able to see any changes on the inputs, I decided to seal in the input status until a reset command is send to the SMS Controller.

Reset Alarms

To reset the input status, send the following command:

####, this will reset the input status.

On your phone, you will receive the following SMS:

i1:0 i2:0 i3:0 i4:0 o1:0 o2:0 03:0 o4:0

Status Updates

You can also request the status at any time by sending the following command:

????, this will request a status update of the I/Os.

On your phone, you will receive the following SMS:

i1:x i2:x i3:x i4:x o1:x o2:x 03:x o4:x

where x indicates the status, 1 for on, 0 for off.

Step 5: Android Application

Using MIT App Inventor 2 (, I created a simple user interface for my Android cellular phone. This app allows you to customise the description of each I/O. It also allows for entry of the telephone number.

The four buttons are used to control the Outputs, while the check boxes indicate the input status.

To edit the app, create a MIT App Inventor 2 account, and import the AIA file.

To install the app on your phone, copy the APK file to your phone, and install it. You will have to enable the installation of apps from "Unknown Sources" under your phone's security settings.

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31 Discussions


6 months ago


I made it with Arduino Nano, tested it, all OK. But after inserting another SIM card, LED that indicates bussy is always ON, and Arduino can not read SMS.

SIM card is new, by same provider as first one. Please if you have some Ideas to solve this. Thank you.

2 replies

The most likely cause for the new sim card not working, is that it doeas not have airtime available to send an SMS.
At boot-up of the unit, the unit will send a SMS to the master user.
You can disable this in line 2119.



// SendSMS(Master_Nr,RxString);

This will disable the boot-up SMS.

Hope this will help.



Thank you Eric.
I solved this thanks to Your Advice and I changed delay time after NetworkTime sync, to leave more time to register on network.
The next thing that happens is that the device after a while loses the Network, signal here is weak. Stable only 2g.
After connecting back on the Network, it receives not the Messages, and sends not reply. Is OK to reset only SIM800L, or complete Unit ?




1 year ago

Hi Finaly this think is working, my arduino was problem,

Thank you very much Eric, This Project is GREAT.

I will add soon readings of temperature and moisture.

1 reply

Hi again

Great news....

You actually made me build the circuit again to test the software. I was just busy when I noticed your comment. Thanks for your feedback.




1 year ago

Hi Eric,

Did you send and receive any sms using GSM_Android_V200.ino and SIM800L ?

I still think that code is not completed.



1 year ago

Hi Eric,

there are 3 "ino" files? what is the procedure to install to arduino uno and connected sim800l without ATMEGA328p


1 reply


I have removed the incorrect ino files. There is now just one file for downloading.

Just upload the sketch to you Arduino Uno as normal.




1 year ago

Hii eric....
Can you code run in sim 808 GPS GPRS GSM BLUETOOTH MODULE ?


1 reply


I am not sure. I only have the SIM800 module.

The commands used for the interface is standard "AT" commands, which is sent serial to the SIM800 module. As most "AT" commands are standard, I am sure that is should work.


can u please tel me how did u create this app?

1 reply

Hi SelvamS5

I used software called MIT App Inventor to create the Android App. You can find it here:

This is an on-line programming tool, and free of charge.

Hope this will help.

Regard, Eric.

how to make it reply on your phone on what is the status of the AC appliances that is connected,

for example it will say POWER ON when i texted to turn it on.

great thanks, i try build my own

Good job Eric and thanks for the AIA file.

I will try to edit it for my own use.


1 year ago

Hi Eric,
Can I use this project SIM900 GSM / GPS module?

2 replies

I think the code will work with the SIM900. The code does not make use of any "special" AT commands, so give it a try.

Ok I disabled this line : //c4 = char(; and now it can be compiled. and I don't know why!!!

hello Eric,

is it possible to use HC-05 bluetooth module instead of GSM? if it's possible what are the changes on the blocks of ai2?