In this project, we will learn How to design a Password Protected BT136 Triac based Keypad Controlled Wireless Home Appliances System with AVR ATmega32 microcontroller using 433MHz RF Part-I. Here, we will use the 4X4 keypad as the input device to enter the password and to control the appliances i.e 2 bulbs and 2 fans. Also, we will display the status of each appliance in the 16X2 alphanumeric LCD. The password is a 4 digit number. In our case the password is “1234” which can be changed in the program. To gain access of the system, the user has to enter the correct password.
The ATmega32 microcontroller will read the 4X4 keypad. First the user will enter the 4 digit password each digit of which will be displayed in a 16X2 alphanumeric LCD as star(*). The microcontroller will compare the entered password with the set password. The system will ask to enter password till the correct password is entered by the user. After the correct password is entered, the microcontroller will read the appliance control signal from 4X4 keypad and it will process the control signal to know which key of the 4X4 keypad is pressed. After knowing which key of the 4X4 keypad is pressed, the ATmega32 microcontroller will send the required 4 bit signal to the HT12E encoder of RF transmitter circuit. The HT12E will encode the 8 bit address and 4 bit data given to it and then it will transmit the encoded signal serially to the RF module. The RF module will transmit the encoded data and address wirelessly. The microcontroller will also display the change in the status of the appliance in the 16X2 alphanumeric LCD.
At the receiver end, the RF receiver module will receive the encoded 4 bit data and 8 bit address. Then, it will transmit the encoded signal serially to the HT12D decoder which will decode the received signal to 8 bit address and 4 bit data. After decoding, the HT12D will compare the received 8 bit address with its local 8 bit address. If the received address and the local address are same, then the received 4 bit data is sent to its output pins else the received data is discarded. The 4 bit output of HT12D is sent to the BT136 Triac Driver to turn on and off appliances.
Here, we will use 2 keys of the Keypad to control one appliance. One key will be used to turn on and the other key will be used to turn off the appliance. So, for four appliances, we will use 8 keys of the keypad. Apart from these 8 keys, we will use 2 more keys to turn on and off all appliances at a time. Now, press different keys of the 4X4 keypad and control your appliances.