Internet Controlled Home-Automation via PLC

Abstract

Power line communication is used to transmit data over power lines which are primarily laid to deliver power from grid to household items. Inside a house power is distributed through a network of wires to all the appliances through several switch boards which are operated manually to control the power flowing to these devices. The concept of home automation is to smartly control these appliances using electromechanical or solid state switches through a microcontroller. Such controllers can be added to each manual switch panel board in the house and can be controlled from a centralized control unit i.e. the server computer. This server computer can be accessed over the internet to control the devices remotely. The centralized control unit communicates with the panel controllers over serial port by sending a device identification and command data. Computer can send commands such as turning the appliances on and off and can receive the data such as the status of a light or the reading of a temperature sensor from these controllers. Conventionally a separate wire has to run from computer to each panel controller to send the serial data from the computer. This increases the system cost and adds extra wiring hassle which is sometimes impossible to implement in finished homes. To avoid extra wiring we can communicate wirelessly between the controllers. The wireless controllers are also very expensive and increase the overall cost of the system. The best alternative solution is to transmit the data over the existing power line cables used to deliver the 220V 50Hz AC power to the appliances. This robust method requires a modem which can transmit and receive data over power lines. The modem has to modulate the serial signal and transmit it over power line through power line coupler along with the existing high voltage AC signal and receive the signal back from power line, separate it from the high voltage AC signal and then demodulate the signal. In this paper we present the design of a binary frequency shift keying (BFSK) modem which modulates the digital data and map it onto mark and space frequencies of 1.5 MHz and 1.1 MHz for the transmission of ones and zeros respectively. The FSK scheme converts the digital data to high frequency signal which can travel on the power lines along with the high power AC signal. This high frequency signal is superimposed on the high power AC signal through a precisely designed power line coupler. On the receiver side a passive band pass filter is used to extract the signal back from the power lines. The designed modem was able to send and receive serial data over single phase 220V power lines within a radius of 15 meters which is enough to cover the perimeter of a house. The modem was successfully used to demonstrate the home automation prototype system and was used to control the devices connected to a computer serial port via power line.