2. 2 BACKGROUND
The use of scrolling display boards for advertisement is becoming common nowadays at various shops, shopping centers, railway and bus stations and other such places. It is becoming an efficient mode for communicating with the general public and providing them information. The problem with such displays is when frequent updating of the messages is required. It becomes inflexible, time consuming and a technician must go compared to that location of display board and plug the computer to it and then update it. it generally does not give the versatility to improve the message from any remote place. Another issue is with the keeping display boards, it can't be placed at any place due to its complex and delicate wiring.
2. 3
To overcome such problems, I designed a GSM based Wireless LED notice board. It is basically a display system that uses real time noticing, b sending messages through cellular phone in the form of SMS. In such system, there is absolutely no dependence on reprogramming the code to update or change the message that should be updated as the complete process is based on wireless technology. A multiplexing method is used to drive the LEDs. And the energy requirement for display module is also reduced.
2. 4 OBJECTIVES
I aimed to develop a moving sign board that can be controlled by the user by sending a SMS. An individual can change the scrolling/display message immediately unlike the old device which requires personal attention at the positioning by using a desk bound device like PC or laptop. My project will let user update it even from a remote distance. After the message is displayed and is also used, it gets deleted from the machine memory to allow new updates to be stored and making space for upcoming SMS. Also, I wanted to design a model which has reduced complexity and simplified hardware and wiring requirements.
2. 5
Wireless technology is an upcoming technology, for this reason reason I planned a project based on it. It implements the wireless communication between a mobile phone and a display board. It runs on the combined feature of microcontroller and wireless technology to construct a precise and effective communication system. An individual makes use of a simple GSM based mobile handset which can only help in sending messages for display purpose via SMS to various display boards. A GSM modem is used at the receiver end which detects and receives upcoming new messages. Proper coding is set in the microcontroller which gives AT commands to read the SMS that is received from the modem which is then stored in the microcontroller.
2. 6
The nature of my project in the beginning was research and survey based along with problem solving. I had developed to consider the safety issue and fast track transmission of the info. The duties I used to be necessary to perform are:
- I was required to divide the project in smaller parts and assign time-duration for every task.
- I was involved with intensive research and analysis predicated on the topic of interest for my project. I had developed to perform survey on various microcontrollers, peripheral devices for e. g. LCD, transmitter and receiver circuits, GSM and so many more based on the need of the project.
- I projected a schematic diagram by making use of ORCAD software.
- I designed the PCB layout.
- After getting the PCB layout I got required to make the hardware structure.
- Which was accompanied by writing the code for the working of the device.
- Lastly, it involved preparation of report and presentation for the entire project.
- It was my duty to keep my project guide updated with the progress of the project.
2. 7 PROFESSIONAL ENGINEERING ACTIVITY
To begin working on my project, I started studying matters appealing and related to my project. After processing and analyzing the info found based on my survey, I started designing the block diagram for my project. I used ORCAD software to create the schematic diagram. It had been a fresh software for me personally, so that it took amount of time in understanding its functions and tools. I structured my drawing in such a way that the project targets the transmission of textual data through air interface with the aid of GSM through asynchronous serial communication. When a unique pass key is entered, the data gets displayed on the LCD. Also, it'll receive and accept data from dedicated and registered user only by performing address matching.
2. 8
Various components which were used are described below:
- Power supply - I used a step-down transformer of 230V primary to 5V secondary voltage that would give a power supply of +5V. This circuit also provides a variable 12V supply to the motor drivers.
- GSM Modem - in the acquiring section, it contains a slot which holds the SIM card. The SIM stores the messages that are sent by an individual. It works on single supply voltage of 3. 4V - 4. 5V.
- Max232 level convertor - this is a dual driver or receiver which acts as an interface medium between the microcontroller and the modem.
- Microcontroller - I used the 89S52 microcontroller which is a 40-pin powerful controller which involves several features. It offers a particular feature of data signal and clock signal which is necessary for scrolling the messages.
- 64x8 LED dot matrix - it is formed by wiring multiple LEDs together in rows and columns. It really is done so that it minimizes the amount of pins that are required to drive them. Each character is displayed by scanning of either rows or columns.
- Shift register IC74LS154 - it is a high speed 8bit Serial-In Parallel-Out shift register. I have used shift register to minimize the number of I/O pins that would be used to operate a vehicle the column of LED matrix.
- Crystal 11. 0592MHz - such quality value crystal assists with reducing the flickering effect that is seen in the LEDs.
2. 9
After finalizing the components, I went ahead to hook up each component to the PCB. After laying out the PCB me and was shown to my project guide for just about any improvement possibility and also to get feedback onto it. After getting the final confirmation from my supervisor I linked the components and completed the full hardware structure. The next task was writing the code because of its functioning. I prepared a flow chart to follow a well-defined path while writing the code. I used keil Microvision software to write my code. It develops a HEX file which can be loaded into the microcontroller. I wrote my programming code in Embedded C language. I divided my employed in two parts, therefore the code was written in two parts.
2. 10
The display process starts by writing '0' on all rows. This may bring about blanking out of most LEDs at the beginning. The microcontroller uses ASCII code for each character that must be displayed. It uses this value to access the corresponding display pattern in a character look up table. The display will be delivered to the display shift register in serial manner. For but with value '1', the LED will be kept off and then for bit with value '0', the LED will be continued. This technique gets repeated for first type of the other five display matrix. And therefore, enabling the first pin. A similar process is repeated for every row till all the rows are displayed. In row scanning, appropriate logic levels are set and passed to the columns and each row is selected for about 1ms time. Thus, making a persistence of vision effect and the image is displayed as a still perceived image. The microcontroller uses and generated a HEX value for each character that should be displayed.
2. 11
The second part involves scrolling of the message. This effect is achieved by defining seven display buffers, each of size 32 bits and stores the bit information of 64x8 LED in the matrix. The scrolling process for displaying the message commences from to left. All the column values for all your rows are shifted to the left direction giving a suitable volume of shift step. This will move the character from to left. After successfully shifting of the type, the row values of next character are taken up. This is done after scrolling it for 5 time per character to accommodate many characters simultaneously. For each and every shift, the display buffer gets updated. Every character is shifted six times to totally load into the display buffer. Thus, the process continues until all the characters in the messages are loaded. After loading of every character, the message will continue steadily to scroll until a fresh message is received. The microcontroller automatically stops the display and extracts the new message from SIM card on the arrival of new message. After that it executes the above cycle for new display process which scrolls down the new message.
2. 12
On completion of the software and hardware part of my project, I performed a test operate on it to check the working of the project. On facing difficulties, I performed troubleshooting on the whole system and gave it a run again. Constant helped was received by my faculty members during any difficulty. Significant problem faced by me was in completing the programming code of the model. As my project's main heart was the program. I referred many software books and coding languages to comprehend the situation and solve it. Another issue was related to the acquiring the signal from the GSM module to the microcontroller. I thought the situation is at the GSM module, but on later analysis of the challenge, I came to know the problem was at the connection, the input pins for the microcontroller was mismatched and soldered in wrong place. To rectify the problem, I studied my circuit diagram again and soldered it to the right place.
2. 13 SUMMARY
To conclude, my project explains each development step I took for designing the GSM based notice board by integrating top features of all hardware components used. Each module is reasoned out and put carefully, thus making the machine to work best. The speed of the display can be managed through the program and the message is displayed as required. Keeping a good scope open for future use in a variety of industries such as food industry, in trains, in educational institute etc. The project gave me a good experience in my own field. I developed many technical skills, managerial skills, and problem solving skills. I believe I made a good use of my academic knowledge that I had developed gained within my bachelor's and applied it to my project. The project was successfully completed on time. I gave weekly report and presentation to the project guide.
