Home Appliances Control Systems Using Phones and RF Remotes

Ever thought how it would be to control your home appliances just with a call from your landline or using a remote or from your smartphone? Great, isn’t it?

Well, this is possible. Instead of wasting your time and energy in manually switching on and off the load every time, you can ease your work just by dialing the required number on your landline phone and accordingly control the particular appliance. You can also just simply use a remote to control the home appliances. Even you can just press a button on your smartphone and control the home appliances

1. Controlling home appliances using a landline

The basic principle involves Dual Tone Multiple Frequency. It involves the generation of a sine wave with high frequencies and low frequencies, for each number pressed on the keypad of the phone. In other words, each decimal number or digit is represented by the linear addition of frequencies. The frequencies in the column side are the high frequencies whereas the frequencies in the row side are the low frequencies.

Thus for each digit pressed, a sine wave signal with dual-frequency is generated. This signal is decoded to get the corresponding BCD equivalent using a DTMF decoder. This BCD signal is again decoded using a Demultiplexer and the obtained signal is inverted and then latched to drive the corresponding relay.

A working example to show the controlling of homemade appliances using DTMF

The system can be developed using the following components:

• A landline Telephone.
• A DTMF decoder
• A Demultiplexer
• Two inverters
• Number of Latch Flip Flops corresponding to each relay(for each load)

Working of the system

The whole system works on the fact that dialing the number 0 connects the telephone line to the appliance mode. When 0 is dialed, the corresponding signal is decoded by the DTMF decoder into the corresponding BCD code. This BCD code is further demultiplexed to obtain high level voltage at the corresponding output of the Demultiplexer. The signal from this output is further inverted and applied to the corresponding Flip Flop. The high signal output from the Flip Flop accordingly energizes a relay. This relay consists of two change over contacts. As the first CO is connected to NO contact, current flows through a resistor, which disconnects the telephone line from the main connection.

A second timer is used to generate a 3KHz tone to give an indication of the telephone working in the appliance model.

For every number pressed on the telephone (other than 0), the procedure is the same. i.e. the decoder generates a corresponding BCD output for the number, which is given to the Demultiplexer. The Demultiplexer generates a low logic signal at the corresponding output (decimal number equivalent to the BCD number) and this low logic signal is further inverted to be latched using the D Flip Flop. The relay connected to the corresponding Flip Flop gets energized and thus drives the connected load to the on condition.

2. Controlling home appliances using RF remote

The basic principle involves transmitting the appropriate signals by pressing the required push button and then receiving these signals to operate the load accordingly. The communication technique used here is RF or radio frequency communication.

Working of the system

The whole system is divided into two parts

• The transmitter unit – The input commands from the pushbuttons are given to the Microcontroller which accordingly converts the commands into binary data and this data is encoded and transmitted via the RF module.
• The receiver unit- The commands are received and decoded and given to the microcontroller to accordingly control the switching of the loads.

 The system involves controlling 4 loads. At the transmitter side, there are four pushbuttons corresponding to each load. When one of the pushbuttons is pressed, the microcontroller on receiving a high pulse from the button converts this number to binary data. This parallel binary data is then given to the encoder. The encoder converts this parallel data to serial form. This serial encoded data is now modulated and transmitted using the RF module.

At the receiving end, the RF module demodulates the received signal and feeds it to the decoder. The decoder decodes this signal to get the original binary data. The microcontroller is programmed to convert this binary data to the decimal number. The optoisolator connected to the corresponding load receives a low logic signal from the microcontroller and triggers the TRIAC. The TRIAC now allows the AC supply to the load and the load gets switched on.

3. Controlling home appliances using a smartphone

A smartphone with a touch screen panel can be used to control the switching of loads. The smartphone is used to communicate with a Bluetooth device and accordingly, the control unit on receiving the commands can control the switching of loads.

The whole system consists of two parts- the transmitter and the receiver. The transmitter is a smartphone with Android software. Bluetooth based application software can be free loaded on the phone with characters that can communicate with a Bluetooth device.

Here the application is a touchscreen-based graphical user interface where buttons are designed to control the switching on and off of each load as well as all loads together.

At the receiver, the Bluetooth device is interfaced to the microcontroller such that the data received by the device is sent to the microcontroller. Based on the data received, the microcontroller accordingly supplies a signal to the relay driver, and the corresponding relay is switched on to switch on the load in turn.

Here using the app on the smartphone, we can switch on any particular load, switch it off or switch on or off all the loads together.