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Password Protected Relay and SIM900 GSM/GPRS Modem based SMS Controlled Wireless Home Automation System with Auto and Status Reply using ATmega16
In this project, we will learn how to make a Password Protected Relay and SIM900 GSM/GPRS Modem based SMS Controlled Wireless Home Automation System with Auto and Status Reply using AVR ATmega16 Microcontroller. Here, we will control home appliances i.e 2 bulbs and 2 fans wirelessly using SIM900 GSM/GPRS modem and ATmega16 microcontroller. The home appliances are controlled by sending SMS to the SIM900 GSM/GPRS modem of the Home Automation System and the change in status of the home appliances are displayed in a 16X2 alphanumeric LCD and if the control SMS is executed successfully, then the Home Automation System sends a reply SMS bearing changed state of the home appliance as message through the SIM900 GSM/GPRS modem to notify the user that the last control SMS has been successfully executed. Also, the current status of all the home appliances can also be inquired at any instant of time by sending a predefined SMS to the SIM900 GSM/GPRS modem of the Home Automation System. But before the Home Automation System can be controlled or status can be inquired or auto reply SMS can be sent, a password needs to be sent by SMS to gain access of the rhome appliance control.
When the SIM900 GSM/GPRS modem power is turned on, the ATmega16 microcontroller reads the initial status data sent by the SIM900 GSM/GPRS modem through USART protocol. After reading the status data, the ATmega16 microcontroller processes the SIM900 GSM/GPRS modem status data and displays the status of the modem and SIM in the alphanumeric LCD. If SIM card is not present, then "Plz Insert SIM" is displayed, if SIM card is present and modem is ready, then "SIM900 is Ready" is displayed and for other conditions, "SIM900 Error" is displayed in the alphanumeric LCD.
Now, when the SIM900 GSM/GPRS modem is ready, the LCD displays "Send Password:" in it. The Home Automation System treats all SMS received as password SMS till the correct password SMS is not received. Once correct password SMS is received and password is authincated, all SMS received after password SMS are treated as control SMS. When the SIM900 GSM/GPRS modem receives any SMS, it sends new SMS notification to the ATmega16 microcontroller. But if the ATmega16 microcontroller receives some other notification(other then SMS like Call and others), then "Unknown Error" is displayed in the alphanumeric LCD. The ATmega16 microcontroller reads the new SMS notification. After reading the SMS notification, ATmega16 microcontroller checks whether password authentication is pending or over. If password authentication is pending, then "PasswordRecieved" is displayed in the LCD display. Then, the ATmega16 microcontroller reads the SMS and if it reads the SMS successfully, then it will compare the content of the SMS with the stored password else it will display"Empty location" when the read memory location is empty and "Error" when there is error in reading the SMS. When the password SMS is read successfully, the ATmega16 microcontroller compares the received password with the the stored password. If the received password and the set password are same, then "Correct Password" is displayed in the alphanumeric LCD else "Re-send Password" is displayed in the LCD. Apart from display in LCD, the status of the password comparision is sent as SMS(Correct Password or Wrong Password) to the mobile number from which the password SMS is received. The Home Automation System will request user to send password SMS till the correct password is sent. Once correct password is sent, the Home Automation System will request the user to send home appliance control SMS and the LCD displays "Send Ctrl SMS:" in 1st row and "All APPli. OFF " in the 2nd row(As all the appliances are in off state initially). The Home Automation System waits for the control SMS to turn On/Off the home appliances. The control SMS are predefined sets of strings(Message of SMS). The predefined set of strings(Message of SMS) to control the home appliances are shown below:-
| Control SMS | Home Appliance Status |
| A1 ON | Bulb 1 On |
| A1 OFF | Bulb 1 Off |
| A12ON | Bulb 2 On |
| A2 OFF | Bulb 2 Off |
| A3 ON | Fan 1 On |
| A3 OFF | Fan 1 Off |
| A4 ON | Fan 2 On |
| A4 OFF | Fan 2 Off |
| ALL ON | All Appliances On |
| ALL OFF | All Appliances Off |
| STATUS | All Appliances Status |
When the SIM900 GSM/GPRS modem receives any SMS after password authentication, it sends new SMS notification to the ATmega16 microcontroller. The ATmega16 microcontroller reads the new SMS notification and displays "New Ctrl SMS" in the alphanumeric LCD. But if the ATmega16 microcontroller receives some other notification(other then SMS like Call and others), then "Unknown Error" is displayed in the alphanumeric LCD. After receiving new SMS notification, the ATmega16 microcontroller will read the SMS from the SIM900 GSM/GPRS modem memory. If it reads the SMS successfully, then it will compare the content of the SMS with the predefined set of strings else it will display "Empty location" when the read memory location is empty and "Error" when there is error in reading the SMS. When the control SMS is read successfully, the ATmega16 microcontroller compares the message of the received control SMS with the predefined ones, if received control SMS matches with any of the predefined strings, then the microcontroller sends the required control signal to the Relay driver to turn On/Off the home appliance and it displays the new status of the home appliance in the alphanumeric LCD. And if the received control SMS matches with the string "STATUS", then the ATmega16 microcontroller reads the current state of all home appliances and sends the AT command to SIM900 GSM/GPRS modem to send status SMS bearing the current state of all home appliances as message to the mobile number from where the status query SMS is received. But if the received control SMS does not matches with any of the predefined SMS, then "Invalid SMS" is displayed in the alphanumeric LCD. For all control SMS received by the Home Automation System, the Home Automation System sends a reply SMS to the mobile number from where the control SMS is received through the SIM900 GSM/GPRS modem. The reply SMS contains changed state of the home appliance as message if the last SMS received is a valid control SMS and reply SMS contains "Invalid SMS" as message if last SMS received is an invalid SMS. The reply SMS is sent to notify the user about the status of the last SMS processed by the Home Automation System. The status of the SMS sending(like SMS Sending, SMS Sent) are also displayed in the alphanumeric LCD.
Now, send different SMS to the SIM900 GSM/GPRS modem of the Home Automation System and see the password comparision, change in state of home appliances, its status in the alphanumeric LCD and whether status and auto reply SMS are sent by the Home Automation System or not.
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Password Protected Relay and SIM900 GSM/GPRS Modem based SMS Controlled Wireless Home Automation System with Auto and Status Reply using ATmega16
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