What is an RF module?
RF radio freguency) module is a small electronic device, to transmit and receive datawirelessly using radio signals. In an embedded system, we often need tocommunicate between two devices wirelessly. We use RF communication onlybecause it doesn't require a line of sight. Several carrier frequencies are commonlyused in commercially available RF modules such as 433MHz, 915MHz and 2400MHZHere wel see about RF 433MHz transmitter and receiver.
RF 433 MHz transmitter and receiver with encoder and decoder:
RF 433MHz transmitter and receiver modules are embedded with HT12e and HT12drespectively.
RF 433 MHz Transmitter:
An RF transmitter module is a small PCB sub-assembly capable of transmitting aradio wave and modulating that wave to carry data. Transmitter modules are usuallyimplemented alongside a microcontroller which will provide data to the module whichcan be transmitted. RF transmitters are usually subject to regulatory requirementswhich dictate the maximum allowable transmitter power output, harmonics, and bandedge reguirements.
RF 433 MHz Receiver:
An RF receiver module receives the modulated RF signal, and demodulates it. Thereare two types of RF receiver modules: superheterodyne receivers and super-regenerative receivers. Super-regenerative nodules are usually low cost and lowpower designs using a series of amplifiers to extract modulated data from a carrierwave. Super-regenerative modules are generally imprecise as their frequency ofoperation varies considerably with temperature and power supply voltage.Superheterodyne receivers have a performance advantage over super-regenerative;they offer increased accuracy and stability over a large voltage and temperaturerange. This stability comes from a fixed crystal design which in the past tended tomean a comparatively more expensive product. However, advances in receiver chipdesign now mean that currently there is little price difference betweensuperheterodyne and super-regenerative receiver modules.
HT12e:
HT12E is a 2^12 series encoder IC, widely used in remote control and very commonamong Radio Frequency RF applications. This HT12E IC is capable of converting 12-bit Parallel data inputs into seria outputs, These bits are classified into 8 (A0-A7)address bits and 4(AD0-AD3) data bits. Using the address pins we can provide 8-bitsecurity code for secured data transmission between the encoder and the decoder.The encoder and decoder should use the same address and data format. HT12E iscapable of operating in a wide Voltage range from 2.4V to 12V and also consists of abuilt-in oscillator.
HT12d:
HT12D is a 2^12 series decoder IC for remote control applications, manufactured byHoltek. It is commonly used for radio frequency (RF) wireless applications. Byusing the paired HT12E encoder and HT12D decoder we can transmit 12 bits ofDarallel data serially. HT12D simply converts serial data to its input (may be receivedthrough RF receiver) to 12-bit parallel data. This 12 bit parallel data is divided into 8address bits and 4 data bits. Using 8 address bits we can provide 8-bit security codefor 4-bit data and can be used to address multiple receivers by using the sametransmitter.
Connections:
RF transmitter with HT12e:
RF transmitter module is embedded with HT12e IC
- VDD and VSS: Positive and negative power supply pins.
- 0SC1 and OSc2: Input and output pins of the internal oscillator present inside theIC.
- TE: This pin is used for enabling the transmission, a low signal in this pin willenable the transmission of data bits.
- A0-A7: These are the input address pins used for secured transmission of thisdata. These pins can be connected to V$S for low signal or left open for high state.
- AD0-AD3: These pins are feeding data into the Ic. These pins may be connectedto VSS for sending LOW since it is an active low pin
- DOUT: The output of the encoder can be obtained through this pin and can beconnected to the RF transmitter.
Experiment:
Working:The aim of this project is to implement a wireless transmitter and receiver using RFmodules. It uses radio signals to transmit the data. The working of the project is asfollows:
The transmitter and receiver sections are placed at a distance. In order to show theworking of wireless communication between transmitter and receiver, 4 LEDs atreceiver side are controlled by 4 buttons at transmitter section (all these LEDs and buttons are inbuilt on the modules).
The HT12E encoder Ic converts the 4-bit data from the 4 data pins that areconnected to buttons into serial data. This serial data is sent to the RF transmitter.The RF transmitter transmits this serial data using radio signals.
At the receiver side, the RF receiver receives the serial data. This serial data is sentto HT12D decoder Ic which converts into 4 bit parallel data. The 4 data pins of thedecoder are connected to LEDs, According to the buttons pushed, the LEDs can beturned ON or OFF.
Applications:
- As RF Modules don't require line of sight communication, the transmitter andreceiver can be isolated over a distance and data can be transmittedsuccessfully.
- The wireless transmitter and receiver can be used in car door and qaragedoor controlers.
- They can also be used in home automation systems.