Multiuser Sms Based Wireless Electronic Notice Board

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Multiuser SMS Based Wireless Electronic Notice Board Abstract— This is the model for displaying notices in colleges on electronic notice board by sending messages in form of SMS through mobile; it is a wireless transmission system which has very less errors and maintenance. The hardware board contains microcontroller AT89c52 at the heart of the system. The microcontroller is interfaced with GSM Modem via MAX232 level convertor. It is used to convert RS232 voltage levels to TTL voltage levels and vice versa. The hardware also has a 64K EEPROM chip AT24C64. This EEPROM is used to store the timings and messages to be displayed. Hardware also contains a real time clock DS1307 to maintain track of time. A 16x2 Character LCD display is…show more content…
B. GSM Modem A GSM modem is a wireless modem that works with a GSM wireless network. A wireless modem behaves like a dial-up modem. The main difference between them is that a dial-up modem sends and receives data through a fixed telephone line while a wireless modem sends and receives data through radio waves. Like a GSM mobile phone, a GSM modem requires a SIM card from a wireless carrier in order to operate. Generally, computers use AT commands to control modems. Reading of message from the SIM card inserted into the modem is done by sending the appropriate AT command to the modem. In addition to the standard AT commands, GSM modems support an extended set of AT commands. These extended AT commands are defined in the GSM standards. Some common basic SMS related AT Commands are shown in table below: [pic] Fig.2. AT Commands C. Display Unit One of the most common devices attached to an 8051 is an LCD display. Here we have used 16x2- that means 2 rows and 16 characters. It is a Hitachi HD44780 compatible module, having 16 pins including 2 pins for backlight. To program the LCD module, first we have to initialize the LCD by sending some control words. RS should be low and E should be high when we send control. R/W pin 0 mean write data or control to LCD and R/W pin 1 means read data from the LCD. To send a data to LCD, make RS high, R/W low, place

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