1. INTRODUCTION TO WIRELESS PC COMMUNICATION
In many situations a communication link between two devices becomes essential. This communication can be wired or wireless. If two devices are close to each other a wired link is preferred. However in many situations two devices are reasonably far apart. In that case a wireless link is preferred. One of the popular wireless communication technologies is RF communication that is being used in our project.
The HT12E and HT12D chips have been used to maintain a wireless link between the two computers. The PC on the transmitter side first transmits the data serially to the microcontroller with the help of voltage converter (MAX232) at an adjusted baud rate. This data is then transmitted to the microcontroller on the receiver side with the help of the wireless link maintained by the RF module. This received data is then sent to the receiver PC serially.
The RS-232 cable (DB-9 connector in this case) is used to coordinate the serial communication between the computer and the microcontroller. The RS232 standard is not TTL compatible, but the 8051 has two pins, that are used specifically for transferring (P3.1) and receiving data (P3.0) serially which are TTL compatible; therefore it requires a line driver such as the MAX232 chip to convert RS232 voltage levels to TTL levels, and vice versa.
Once the microcontroller has serially received data from PC, the RF module comes into operation. For RF communication the HT12E IC installed at the transmitter side sends 12 bit data (8-bit address and 4-bit data) to the HT12D IC at the receiver side. If the 8-bit address at both the IC’s matches then 4-bit data is transmitted successfully to the microcontroller at the receiver side. Next the data is sent to the PC from the microcontroller via serial communication in a similar manner as in the case of the transmitter.
2. LITERATURE SURVEY
‘The 8051 Microcontroller and Embedded Systems’ by Muhammad Ali Mazidi, Janice Gillispie and Rolin D. McKinlay, 2nd edition was referred for the interfacing of 8051 microcontroller with the computer that required line drivers such as MAX 232 chip to convert RS232 voltage levels to TTL levels and vice versa. The RS232 standard is not TTL compatible; therefore, it requires a line driver such as the MAX 232 chip. The RS232 standard is an interfacing standard that was set by the Electronics Industries Association (EIA). The RS232 cable used in our project is the DB-9 connector.
‘The 8051 Microcontroller’ by Kenneth J. Ayala, 3rd edition was referred to study the basic concepts of serial communication and the advantages of serial communication over parallel communication.
The link http://extremeelectronics.co.in/avr-tutorials/rf-communication-between-microcontrollers-part-ii/ was referred for a detailed description of RF communication between microcontrollers with the help of HT12D and HT12E ICs. The 2^12 decoders are a series of CMOS LSIs for remote control system applications. They are paired with Holtek 2^12 series of encoders. For proper operation, a pair of encoder/decoder with the same number of addresses and data format should be chosen.
The main objective of this project is to display the data transmitted by one PC on another PC and hence establish a wireless link between two PC’s. RF communication is one of the popular wireless communication technologies. The RF transmitter and receiver section consists of HT12E and HT12D IC’s respectively. Here for both the IC’s the first 8 pins contribute to an 8-bit address. The data is transmitted only if the address at pins A0-A7 of HT12E (transmitter) matches with the address at pins A0-A7 of HT12D (receiver). The logic levels present at the Holtek HT-12E encoder pins D0-D3 will be transferred to the receiver i.e. at pins D0-D3 of HT12D. The circuit will transmit continuously if the pin #14 (TE) of HT12E is left connected to ground. The Holtek...
References:  Li-Jun Lai (2009),"radio remote control of appliances", paper, Institute of Electrical Engineering, National Yunlin University of Science and Technology, Touliu, Yunlin 640, Taiwan.
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