31-10-2012, 03:58 PM
Implementation of Wireless Communication using the PIC 16f877A Micro controller.
Implementation of Wireless.doc (Size: 3.63 MB / Downloads: 31)
ABSTRACT
In this project work the basic and essential concepts of radio communication were utilized to create a wireless communication channel between two Computers. One computer is placed at the transmitter section. In this section we can see the display of the parameter values. The second computer is placed at the receiving end, where the maintenance persons are monitoring the system. Here we can monitor the parameters condition continuously. A PIC micro-controller (16f877A) and MAX232, RS232 are used as interfacing units between the system and RF transmitter and also at the receiver section. The program code is written in Assembly language and the serial communication concept is used to transfer the data. This project can be used as an alternate to wireless communication.
INTRODUCTION
The project report describes on the design development and fabrication of one demo unit of the project work “Implementation of wireless communication between computers”.
Now a day, with the advancement technology, particularly in the field of Micro-controllers, all the activities in our daily living have become a part of Information Technology and we find micro-controllers in each and every application. Thus, trend is directing towards Microcontrollers Based Project works. However, in this project work, the transferring of data serially is monitored. Subsequently, after serial processing, these signals are encoded. This information is transmitted through RF transmitter. The received information (using suitable RF receiver) is again decoded into digital signal at the receiver end. Then the decisions are taken with the help of micro-controllers and associated software.
The micro-controller block is playing a major role in this project work. The Micro-controller chip is used in this project work is PIC 16f877A, and this is like heart of the project work. The PIC micro-controller is 40 pin IC.
Micro controllers are “embedded” inside some other device so that they can control the features or actions of the product. Another name for a micro-controller, therefore, is “Embedded Controller”. Micro controllers are dedicated to one task and run one specific program. The program is stored in ROM (read only memory) and generally does not change. Micro controllers are often low-price devices. A battery operated micro-controller might consume 50 mille watts. A micro-controller has a dedicated input device and often (but not always) has a small LED or LCD display for output.
EMBEDDED SYSTEMS:
A system is something that maintains its existence and functions as a whole through the interaction of its parts. E.g. Body, Mankind, Access Control, etc A system is a part of the world that a person or group of persons during some time interval and for some purpose choose to regard as a whole, consisting of interrelated components, each component characterized by properties that are selected as being relevant to the purpose.
• Embedded System is a combination of hardware and software used to achieve a single specific task.
• Embedded systems are computer systems that monitor, respond to, or control an external environment.
• Environment connected to systems through sensors, actuators and other I/O interfaces.
Implementation
To implement the wireless RS232 interface two different circuit boards will be designed. The two boards will consist of a transmitter and receiver. The transmitter will accept data from a RS232 (9-pin) of a PC port and transfer the information to RF signal. The receiver will capture the RF signal, transferring it back to a digital signal, and finally import it into the RS232 (9-pin) port of a PC. The purpose of the rest of this document is to specify the integration of this RF technology
DETAILS ABOUT MICROCONTROLLER
The micro-controller is a chip, which has a computer processor with all its support function, memory (both program storage and RAM), and I/O built in to the device. These built in functions minimize the need for external circuits and devices to design in the final applications.Most microcontrollers do not require a substantial amount of time to learn how to efficiently program them, although many of then which have quirks which you will have to understand before you attempt to develop your first application.
Along with micro-controllers getting faster, smaller and more power efficient they are also getting more and more features. Often, the first version of micro-controller will just have memory and digital I/O, but as the device family matures, more and more pat numbers with varying features will be available.
With all the 8052 manufactures products taken into the account, there are over two hundred different 8052 part numbers, each with different features and capabilities. For most applications, we will be able to find a device within the family that meets our specifications with a minimum of external devices, or an external but which will make attaching external devices easier, both in terms of wiring and programming.
For many micro controllers, programmers can be built very cheaply, or even built in to the final application circuit eliminating the need for a separate circuit. Also simplifying this requirement is the availability of micro-controllers with SRAM and EEPROM for control store, which will allow program development without having to remove the micro controller from the application circuit.
MAX232 Connector
The MAX232 connector will be used to transfer data from the MAX232 (16-pin) port of a PC to the input line converter. The connector will be a 90-degree flat mount design that will allow the pins of a serial connection to be transferred to data lines in a PC board. A typical model would be 182-09F-ND Right Angle D-Sub connector made by Norcomp.
Power Supply
The AC main Block is the power supply which is of single phase 230V ac. This should be given to step down transformer to reduce the 230V ac voltage to low voltage. i.e., to 6V or 12V ac this value depends on the transformer inner winding. The output of the transformer is given to the rectifier circuit. This rectifier converts ac voltage to dc voltage. But the voltage may consist of ripples or harmonics.
To avoid these ripples the output of the rectifier is connected to filter. The filter thus removes the harmonics. This is the exact dc voltage of the given specification. But the controller operates at 5V dc and the relays and driver operates at 12V dc voltage. So we need a regulator to reduce the voltage. 7805 regulator produces 5V dc and 7812 regulator produces 12V dc. Both are positive voltages.
Encoder-Buffer
The Encoder-Buffer is to be designed to condition the signal for the transmitter by adding error detection and encoding. i.e. how 0’s and 1’s will be declared. One proposal for is to use Manchester encoding. Manchester encoding uses logic of a high to low as 0 and low to high as a 1. That implies that every bit period is divided into two and insures that the transaction from high to low or low to high is in the middle of each period. By creating this phenomenon we allow the transmitter to synchronize with the receiver at every bit. With this we will be able to maximize reliability and implement techniques to assist in error detection.
Amplitude Shift Keying
ASK- in the context of digital communications is a modulation process, which imparts to a sinusoid two or more discrete amplitude levels. These are related to the number of levels adopted by the digital message. For a binary message sequence there are two levels, one of which is typically zero. Thus the modulated waveform consists of bursts of a sinusoid binary ASK signal (lower), together with the binary sequence which initiated it (upper). Neither signal has been band limited. There are sharp discontinuities shown at the transition points. These result in the signal having an unnecessarily wide bandwidth. Band limiting is generally introduced before transmission, in which case these discontinuities would be ‘round off’. The band limiting may be applied to the digital message, or the modulated signal itself. The data rate is often made a sub-multiple of the carrier frequency. One of the disadvantages of ASK, compared with FSK and PSK, for example, is that it has not got a constant envelope. This makes its processing (e.g., power amplification) more difficult, since linearity becomes an important factor. However, it does make for ease of demodulation with an envelope detector.
CIRCUIT DESCRIPTION
POWER SUPPLY:
Power supply unit consists of Step down transformer, Rectifier, Input filter, Regulator unit, Output filter.
The Step down Transformer is used to step down the main supply voltage from 230V AC to lower value. This 230 AC voltage cannot be used directly, thus it is stepped down. The Transformer consists of primary and secondary coils. To reduce or step down the voltage, the transformer is designed to contain less number of turns in its secondary core. The output from the secondary coil is also AC waveform. Thus the conversion from AC to DC is essential. This conversion is achieved by using the Rectifier Circuit/Unit.
The Rectifier circuit is used to convert the AC voltage into its corresponding DC voltage. There are Half-Wave, Full-Wave and bridge Rectifiers available for this specific function. The most important and simple device used in Rectifier circuit is the diode. The simple function of the diode is to conduct when forward biased and not to conduct in reverse bias.
The Forward Bias is achieved by connecting the diode’s positive with positive of the battery and negative with battery’s negative. The efficient circuit used is the Full wave Bridge rectifier circuit. The output voltage of the rectifier is in rippled form, the ripples from the obtained DC voltage are removed using other circuits available. The circuit used for removing the ripples is called Filter circuit.