Controlling Appliances Wirelessly Using RF Technology
Roberto Magalhães
REQUIREMENTS:
1. Encoder/Decoder (HT12E/HT12D)
2. RX/TX Module (433 MHz)
3. SPDT Switches (4)
4. Relays (4) {to handle 220 AC voltage}
5. 7805 voltage regulator IC
6. L293d {for 12V relay operation}
Nowadays everyone needs a device that can control devices wirelessly. This allows us to operate them at our fingertips in specific locations with ease.
This time I created a prototype of a device that controls 4 devices/household appliances separately using RF (Radio Frequency) technology. The device comprises two sections: transmitting (remote) part and receiving part.
The transmitting part works as a remote device to send corresponding data to the receiving section. It also consists of 4 SPDT switches (single pole double throw), an Encoder IC (HT12E) and a TX module (433 MHz). These 4 switches are connected to the 4 data pins of the encoder IC to generate 4-bit data to be transmitted. The switches provide high (+5V) or low (0V) signal levels.
On the receiver part, this 4-bit data is received wirelessly by the decoder IC via RX module and then the corresponding output is provided on the data pins of the decoder. The 4 relays are connected to these 4 data outputs that only react to the high state (+5V), that is, for (+5V) it will remain on and for (0V) it will turn off. This technique also helps to operate devices that operate with a voltage of 220 AC.
Figure 1:
Image of 433 MHz RF transmitter and receiver modules
Figure 2: Prototypes of 433 MHz RF transmitter and receiver modules based on HT12E and HT12D ICs
ABOUT Encoder/Decoder:
Encoders and decoders are used when we need to send our data serially. The pair of encoders and decoders I used are HT12E/HT12D respectively. These are 18-pin ICs.
These encoders/decoders require 12 bits for communication, of which 8 are address pins and the remaining four are data pins. For a pair of these encoders/decoders to work together, their addresses must match, only then will the data be decoded on the decoder part.
The figure below represents how the wave is generated for communication to occur:
Now here the first 8 (1-8) pulses correspond to the address pins and the 9-12 pulses are the data pins.
Since there are only 4 bits for data communication, this makes it a 4-bit data encoder/decoder IC.
These encoders/decoders also require a clock pulse on pins 15 and 16, which can be provided by simply connecting these two pins through a specified resistance. I used 1M Ohm for the encoder part while the decoder works with 33K Ohm (these values are specified in its datasheet).
To learn more about these ICs visit the links below:
(CODER):
(DECODER):
ABOUT RF module:
These modules are really simple to deal with. They only require a VCC (+5V), GND (0V) and DATA connection. Some of them also need ANTENNA (ANT) connection. The module I used works at 433 MHz frequency to transmit data wirelessly.
Now the question arises is how to interface Rx/Tx with our Decoder/Encoder part. It's very simple; Simply connect the encoder's data output pin with the Tx data pin and the Rx data pin with the decoder's data pin.
