The communication technology had its debut with wired communication. The wired communication is still popular and used wide-spread for telephony and internet. Though it was soon realized that wired communication has its own limitations. Its installation incurs high cost and the installation becomes more complicated as the system grows. Moreover wired communication was never a suitable medium for many consumer electronics, industrial and military applications. Then, the discovery of electromagnetic waves and their application in communication came as a great advancement for the mankind.
The world was first introduced to wireless communication when Guglielmo Marconi developed first wireless telegraph system in 1896. The technology progressed in early 1900s with the introduction of commercial radiotelephony and by 1960s first communication satellites were in space. Another decade saw the introduction of cellular systems and mobile communication sought to became a norm by late 1980s in the developed countries. Till this time, use of radio communication for mobile telephony, television broadcasting and satellite and radio based communication for military applications had gained full momentum.
From 1990s onwards wireless communication found a different dimension apart from its use in telecommunication, military and space applications. This was the use of low-band radio frequency communication for data transfer to smaller distances. The telecommunication sector utilized this by introducing the technologies like Bluetooth for transferring data from one device to another over few meters and Wi-Fi for routing internet wireless in a home or office environment. The consumer electronics sector also utilized these standard wireless communication technologies and additionally utilized other low band radio frequency technologies for equipping their appliances with remote control and wireless data transfer.
The performance of any wireless system is judged based on two parameters - distance it can transfer data and the rate (data rate) at which it can transmit and receive data. The wireless systems use a wide range of frequencies from 30 KHz to 300 GHz. The higher the frequency higher is the distance of operation. For small distance communication, low band frequencies of few KHz or MHz are used.
The following project is also a demonstration of low-band radio frequency communication using a 434MHz RF module. These kinds of radio communication modules have distinct advantages over other remote control technologies like the infrared. These modules do not need a line of sight for operation and they can be used over a wide array of operating voltages ranging from 3V to 12V.
How Radio Frequency Communication Works
Like any communication system, RF systems also have a transmitter end which transmits electromagnetic waves with data encoded in them and a receiver end which receives these waves and retrieve data from them.
Several carrier frequencies are commonly used in commercially-available RF modules, including those in the industrial, scientific and medical (ISM) radio bands such as 433.92 MHz, 915 MHz, and 2400 MHz the selection of 434MHz among these frequencies is because of national and international regulations governing the use of radio frequency for communication. Short Range Devices can also use frequencies such as 315 MHz and 868 MHz available for unlicensed use.
At the transmitter end, the electromagnetic waves need to be modulated for encoding data in them. Here modulation means that one of the characteristic of the wave like amplitude, frequency or sequence is changed according to the digital data that has to be transferred. There are a myriad of modulation techniques like ASK, OOK, FSK, Direct sequence spread spectrum, Frequency hopping spread spectrum and GFSK which are used by radio communication systems for representing data. The selection of the modulation technique depends on the application and requirements. The modulation technique used in this 434 MHz RF module is ASK (Amplitude Shift Keying) which is the most commonly used modulation technique in low band radio communications.
At the receiver end, a reverse process called demodulation using the same demodulation technique (ASK in this case) is carried out and the data is extracted from the carrier wave.
One important aspect of working with RF modules is the identification of transmitter and receiver with respect to each other. This is called pairing. It is done by matching an identification key set at both ends. The data is serially transmitted and received. Thus data from a microcontroller or processor may need to be serialized using an encoder and at the receiver end it may need to be decoded using a decoder for parallel data transfer. The encoder and decoder ICs used in this module are HT12E and HT12D respectively.
|RF Transmitter and receiver module ( 434 MHz)||1|
|HT12E/HT12D Encoder IC||1|
|Resistor - 10KΩ (Quarter watt)||8|
|Resister-1MΩ (Quarter watt)||1|
|Connecting Wires|| |