RF Module – Transmitter & Receiver What is RF Module? In general, the wireless systems designer has two overriding constraints: it must operate over a certain distance and transfer a certain amount of information within a data rate. The RF modules are very small in dimension and have a wide operating voltage range i.e. 3V to 12V. Basically the RF modules are 433 MHz RF transmitter and receiver modules. The transmitter draws no power when transmitting logic zero while fully suppressing the carrier frequency thus consume significantly low power in battery operation. When logic one is sent carrier is fully on to about 4.5mA with a 3volts power supply. The data is sent serially from the transmitter which is received by the tuned receiver. Transmitter and the receiver are duly interfaced to two microcontrollers for data transfer. Features of RF Module: Receiver frequency 433MHz Receiver typical frequency 105Dbm Receiver supply current 3.5mA Low power consumption Receiver operating voltage 5v Transmitter frequency range 433.92MHz Transmitter supply voltage 3v~6v Transmitter output power 4v~12v Main Factors Affecting RF Module’s Performance: As compared to the other radio-frequency devices, the performance of an RF module will depend on several factors like by increasing the transmitter’s power a large communication distance will be gathered. However, which will result in a high electrical power drain on the transmitter device, which causes a shorter operating life of the battery-powered devices. Also by using this device at higher transmitted power will create interference with other RF devices. 4 Applications: Wireless security systems Car alarm systems Remote controls Sensor reporting Automation systems 3 RF Modules 1. 433 MHz RF Transmitter and Receiver: In many projects, we use RF modules to transmitting and receive the data because it has a high volume of applications than IR. RF signals travel in the transmitter and receiver even when there is an obstruction. It operates at a specific frequency of 433MHz. RF transmitter receives serial data and transmits to the receiver through an antenna which is connected to the 4th pin of the transmitter. When logic 0 applied to transmitter then there is no power supply in the transmitter. When logic 1 is applied to transmitter then the transmitter is ON and there is a high power supply in the range of 4.5mA with 3V voltage supply. Video on 433 MHz RF Transmitter and Receiver: Features of RF Transmitter and Receiver: Receiver frequency: 433MHz Receiver typical sensitivity: 105Dbm Receiver current supply: 3.5mA Receiver operating voltage: 5V Low power consumption Transmitter frequency range: 433.92MHz Transmitter supply voltage: 3V~6V Transmitter output power: 4~12Dbm It has many applications in various areas like Remote lighting controls, long-range RFID, wireless alarm and security systems, etc. RF Transmitter Circuit: RF Transmitter Circuit RF Receiver Circuit: RF Receiver Circuit 2. XBee Module: What is the XBee Module? XBee modules are wireless communication modules that are built based on the Zigbee standard. It utilizes the IEEE 802.15.4 protocol. Zigbee standards are standards with a range between Bluetooth and WIFI. They are basically RF modules. Wireless technology can be challenging without the right combination of expertise and resources. The XBee is an arrangement of modular products that make deploying wireless technology easy and cost-effective. The module can communicate up to 100 feet indoors or 300 feet outdoors. It can be used as a serial replacement or you can put it into a command mode and configure it for a variety of broadcast and mesh networking options. The XBee modules provide wireless connectivity to devices. XBee and XBee-PRO RF modules are embedded solutions furnishing wireless end-point connectivity to systems. XBee modules are for extended-range applications and they are intended for high-throughput applications requiring low latency and predictable communication timing. And they are ideal for low power and low-cost applications. The very popular XBee module is 2.4GHz from Digi. These modules allow a very reliable and basic communication between microcontrollers, PCs, systems, and support point to point and multi-point networks. Features of XBee Module: Complete RF transceiver Onboard data encryption Automatic collision avoidance Low current consumption Wide operating voltage 1.8-3.6 Volts Operating frequency: 2.4-2.483 GHz Programmable output power and high sensitivity Data rate 1.2-500 kbps The transceiver module furnishes a complete RF subsystem that can be utilized to transmit and receive data at up to 500Kbps from any standard CMOS/TTL source. Extensive hardware support is provided for packet handling, information buffering, burst transmissions, and link quality implication. Automatic collision avoidance is additionally given with clear channel evaluation features. The modules are ideal for battery-powered applications. How XBee Module Works: From the below circuit, we used two trans-receiver 2.4GHz XBee modules for two computers. The interfacing from the XBee modules is done through level shifter IC MAX232 as shown in the figure. The modules are powered by onboard regulated 3.3V power supply meeting the voltage requirement of the device by 3.3V regulator being fed after getting the 5V from the regulator. In order to draw the attention of the recipient computer for the message received from the sender computer, an audio beeping system is interfaced from the MAX232 Transmitter pin duly inverted two times by a pair of transistors Q1 and Q2 (BC547) to a 555 monostable multi-vibrator through its triggering pin2. Thus while any message is received at the transmitter pin of the MAX232 it also reaches the base of the Q1 resulting triggering of 555 monostable multi-vibrator timer to output from pin3 a buzzer sound. Hence it draws the attention of the recipient computer to respond to the message. R6, RV1, C10 form the time constant of the monostable timer 555 for the duration of the buzzer sound every time a keyboard key is pressed by the sender. It also has a provision to change the time constant by varying the RV1 to suit the recipient’s convenience. 3. 3-Pin RF Module: How 3-pin RF Module Works in sending the secrete information? We can connect the 3-pin RF modules directly to the controller; there is no need of any encoder and decoder. The working of the 3-pin RF transmitter and receiver modules is as follows in sending/transforming the secrete information. Working of RF Transmitter Module: From the circuit, the power supply +5V is connected to the 40 pins of the microcontroller, and the ground is connected to the 20th pin. Here, we got two switches that are duly connected to the microcontroller with pulled up to 5V and these two switches form the input command to the microcontroller. We also got an LCD display for displaying the data to be transmitted. We also have an arrangement for a computer keyboard to be connected for positive and negative parts from the clock and data pin which is connected as an input to the microcontroller from the output of keyboard and that data is ultimately displayed in the LCD. We also have one RF transmitter. It has a VCC supply, GND. The data pin goes to the microcontroller. The program is so written that by appropriate operation of this working we first make the keyboard active. Once the keyboard is made active by pressing the buttons then the keyboard entry can take place which is displays in LCD. If it has to be sent against codes varying from 0 to 9 this will be displayed in LCD. Here every press is advancing as per the code from 0 to 9 and ultimately when we press one of the push-button for sending it will go to a microcontroller and then to the RF transmitter module over a 433 MHz frequency transmitted from the antenna. Working of RF Receiver Module: At the receiver end, we have similar connections for power supply as microcontroller needs +5V. Similarly to the transmitter, hear also we are using two pushbuttons with 10k pull up resistors through 5V supply for RF Module. We are using pin 3.0 to connect the data pin of the RF module and 1 and 2 pins of the RF module are used for GND and VCC. We also have two buttons for the selection of code and for receiving the data. Once the data is received by the receiver module that data is demodulated and goes to the receiver pin 10 of the microcontroller as per the program. It then displays the message on the LCD display. Features: Receiver frequency 433MHz Receiver typical frequency 105Dbm Receiver supply current 3.5mA Low power consumption Receiver operating voltage 5v Transmitter frequency range 433.92MHz Transmitter supply voltage 3v~6v Transmitter output power 4v~12v 2 Applications involving RF Module 1. Remote operated Robotic Vehicle Working: The robot is a moving vehicle remotely controlled by one transmitting unit and a receiving unit for its moment. In this, we used an HT12E encoder which converts 4-bit data to serial output. As explained above this is then fed to the RF module for transmitting the same to be received by the receiver. The RF module the output is fed to HT12D the serial decoder IC, the output of which is fed to microcontroller pin 1 to 4. The transmitting end microcontroller is connected to a set of pushbutton switches to its port 3 of 20 pin microcontroller AT89C2051. Thus while a particular button is pressed the program is executed to deliver corresponding 4-bit data which are then transmitted serially at port 1 as explained above. The data so received at the receiver end of port 1 of the Microcontroller. Laser light is driven by transistor Q1 from the output of microcontroller pin 15, while the robotic vehicle is maneuvered to the location by operating the left, right, forward and backward button, etc. after it reaches the site the laser mounted on it takes position to throw the beam by operating specific action button. 2. Robotics without Microcontroller Circuit Diagram: Pin14 of encoder HT12E is given a low logic signal as data signals work on negative logic. The encoder converts the parallel signals to serial format and transfers them through the RF transmitter at a rate of 1 to 10kbps. The signals are decoded back to parallel signals by the decoder IC HT12D after being received by the receiver. The signals after being inverted are then applied to the motor driver IC, to drive the motor. By varying the logics applied to pins 2, 7, 10, and 15, the motor directions can be changed. 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