04-10-2012, 05:12 PM
SMS Based Wireless Electronic Notice Board using Embedded System
SMS Based Wireless.docx (Size: 2.31 MB / Downloads: 826)
ABSTRACT:
Notice Board is primary thing in any institution / organization or public utility places like bus stations, railway stations and parks. But sticking various notices day-to-day is a difficult process. A separate person is required to take care of this notices display. This project deals about an advanced hi-tech wireless notice board. The project is built around the 8051 micro controller. This micro controller provides all the functionality of the display and wireless control. It also takes care of creating different display effects for given text. Display is obtained on LED Matrix Display Array on a printed circuit board. A GSM Mobile Can is used to enter the required text or notice. The scrolling speed of the text also can be changed according to user requirement.
After entering the text the SMS is sent to the no which is connected to the LED display. At any time the user can add or remove or alter the text according to his requirement. At the receiving end the GSM modem which is connected to the Max 232 receives the message and is connected to the 8051 microcontroller. The message is displayed on the LCD Display. This project uses regulated 5V, 500mA power supply. 7805 three terminal voltage regulator is used for voltage regulation. Bridge type full wave rectifier is used to rectify the ac output of secondary of 230/12V step down transformer.
INTRODUCTION
Notice Board is primary thing in any institution / organization or public utility places like bus stations, railway stations and parks. But sticking various notices day-to-day is a difficult process. A separate person is required to take care of this notices display. This project deals about an advanced hi-tech wireless notice board.
An embedded system is a combination of software and hardware to perform a dedicated task. Some of the main devices used in embedded products are Microprocessors and Microcontrollers, Microprocessors are commonly referred to as general purpose processors as they simply accept the inputs, process it and give the output. In contrast, a microcontroller not only accepts the data as inputs but also manipulates it, interfaces the data with various devices, controls the data and thus finally gives the result. As everyone in this competitive world prefers to make the things easy and simple to handle, this project sets an example to some extent.
This project is built around the 8051 micro controller. Micro controller provides all the functionality of the display and wireless control. It also takes care of creating different display effects for given text. Display is obtained on LCD Display on a printed circuit board. A GSM Mobile Can is used to enter the required text or notice. The scrolling speed of the text also can be changed according to user requirement.
After entering the text the SMS is sent to the no which is connected to the LCD display. At any time the user can add or remove or alter the text according to his requirement. At the receiving end the GSM modem which is connected to the Max 232 receives the message and is connected to the 8051 microcontroller.
EXPLANATION OF POWER SUPPLY
The input to the circuit is applied from the regulated power supply. The a.c. input i.e., 230V from the mains supply is step down by the transformer to 12V and is fed to a rectifier. The output obtained from the rectifier is a pulsating d.c voltage. So in order to get a pure d.c voltage, the output voltage from the rectifier is fed to a filter to remove any a.c components present even after rectification. Now, this voltage is given to a voltage regulator to obtain a pure constant dc voltage.
TRANSFORMER:
Usually, DC voltages are required to operate various electronic equipment and these voltages are 5V, 9V or 12V. But these voltages cannot be obtained directly. Thus the a.c input available at the mains supply i.e., 230V is to be brought down to the required voltage level. This is done by a transformer. Thus, a step down transformer is employed to decrease the voltage to a required level.
RECTIFIER:
The output from the transformer is fed to the rectifier. It converts A.C. into pulsating D.C. The rectifier may be a half wave or a full wave rectifier. In this project, a bridge rectifier is used because of its merits like good stability and full wave rectification.
FILTER:
Capacitive filter is used in this project. It removes the ripples from the output of rectifier and smoothens the D.C. Output received from this filter is constant until the mains voltage and load is maintained constant. However, if either of the two is varied, D.C. voltage received at this point changes. Therefore a regulator is applied at the output stage.
VOLTAGE REGULATOR:
As the name itself implies, it regulates the input applied to it. A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage level. In this project, power supply of 5V and 12V are required. In order to obtain these voltage levels, 7805 and 7812 voltage regulators are to be used. The first number 78 represents positive supply and the numbers 05, 12 represent the required output voltage levels.
RS232 CABLE:
To allow compatibility among data communication equipment, an interfacing standard called RS232 is used. Since the standard was set long before the advent of the TTL logic family, its input and output voltage levels are not TTL compatible. For this reason, to connect any RS232 to a microcontroller system, voltage converters such as MAX232 are used to convert the TTL logic levels to the RS232 voltage levels and vice versa.
8051 Memory Organization
Before going deep into the memory architecture of 8051, lets talk a little bit about two variations available for the same. They are Princeton architecture and Harvard architecture. Princeton architecture treats address memory and data memory as a single unit (does not distinguish between two) where as Harvard architecture treats program memory and data memory as separate entities. Thus Harvard architecture demands address, data and control bus for accessing them separately where as Princeton architecture does not demand any such separate bus.
SPECIAL FUNCTION REGISTER:
“Special Function Registers” known with an acronym SFR. There are 21 Special function registers (SFR) in 8051 micro controller and this includes Register A, Register B, Processor Status Word (PSW), PCON etc etc. There are 21 unique locations for these 21 special function registers and each of these register is of 1 byte size. Some of these special function registers are bit addressable (which means you can access 8 individual bits inside a single byte), while some others are only byte addressable. Let’s take a look at them in detail.
Register A/Accumulator:
The most important of all special function registers, that’s the first comment about Accumulator which is also known as ACC or A. The Accumulator (sometimes referred to as Register A also) holds the result of most of arithmetic and logic operations. ACC is usually accessed by direct addressing and its physical address is E0H. Accumulator is both byte and bit addressable. You can understand this from the figure shown below. To access the first bit (i.e bit 0) or to access accumulator as a single byte (all 8 bits at once), you may use the same physical address E0H. Now if you want to access the second bit (i.e bit 1), you may use E1H and for third bit E2H and so on.
Stack Pointer:
Known popularly with an acronym SP, stack pointer represents a pointer to the the system stack. Stack pointer is an 8 bit register, the direct address of SP is 81H and it is only byte addressable, which means you cant access individual bits of stack pointer. The content of the stack pointer points to the last stored location of system stack. To store something new in system stack, the SP must be incremented by 1 first and then execute the “store” command. Usually after a system reset SP is initialized as 07H and data can be stored to stack from 08H onwards. This is usually a default case and programmer can alter values of SP to suit his needs.
Power Management Register (PCON)
Power management using a microcontroller is something you see every day in mobile phones. Haven’t you noticed and got wondered by a mobile phone automatically going into stand by mode when not used for a couple of seconds or minutes ? This is achieved by power management feature of the controller used inside that phone.
As the name indicates, this register is used for efficient power management of 8051 micro controller. Commonly referred to as PCON register, this is a dedicated SFR for power management alone. From the figure below you can observe that there are 2 modes for this register :- Idle mode and Power down mode.