Ever since its evolution, Global System for Mobiles(GSM) is the most reliable communication protocol.Applications of GSM are numerous one such application is Notice Board Display. In remote areas to convey emergency information Notice Board plays vital role.Basic Prototype of Notice Board display
GSM: SIM 900 is the most commonly used GSM module.
Serial module has two levels i) RS-232 can be directly used to communicate with PC.
ii) TTL most of the Microcontrollers operate at this level.
specialty of this module is either you can go for Asynchronous communication protocol like(UART)
or Synchronous communication protocol(I2C).
It can be powered form 5V DC adapter which should supply at least 1.5 to 2 A of current.
Precisely it works at 3.3 to 4.7 volts. Most of the Micro-controller boards have on board Vcc (5V) pin but it may not provide (1.5 A) current. To drive GSM module using on board Vcc a Capacitor of large value(0.1 Farad) is required which should be connected in parallel to load(GSM) module.
If supply voltage is less than 3.3v Module gives "Under-Voltage warning" If supply voltage is greater than 4.7 V Module gives "Over-Voltage warning".
To drive GSM module using on board supply (5V) following circuit can be used.
CC-mode is preferred as It has good Current gain. capacitor provides relevant storage (current source) that can be sufficient to drive GSM module.
Before programming,GSM can be configured directly using Serial(DB9) cable (RS-232)or by using USB-TTL converter(TTL). Hyper-Terminal or any software like Cool-Term can be used to communicate with module.Connect Tx of GSM to Tx of (DB9 or USB-TTL) similarly Rx of GSM to Rx of(DB9 or USB-TTL).
Alternative way to Drive GSM module using DC Adapter which should give sufficient power to drive GSM in Full Function mode. I bought this adapter for 100 Rs from Koti.
Initially to communicate with GSM module you can go for any USB-to-TTL/CMOS converter which requires USB class B cable, I used this,
Pin out this xbee (USB-CMOS ) converter from Tx end.
1. VCC 2. TX 3. Rx ....... 10. Gnd
connect Tx of GSM to Tx of xbee
Rx of GSM to Rx of xbee
GND of GSM to GND of xbee
Use Coolterm on PC to check whether GSM module is responding properly or not
xbee through USB class B cable when connected to PC it should show virtual com on screen you can Identify in following way
Right click on computer, click on properties then click on Device Manager then expand Ports(COM & LPT) there you can see one virtual com because of Xbee(USB-CMOS) converter Make note of that COM number and use same port to communicate with GSM module in my case it is COM 15
Open Coolterm click on options and select settings as shown use baud rate of 2400 so that communication will be at low speed so that chance of data loss will be less.
on coolterm you should get following message
other wise type AT+CFUN=1 IT should respond with OK
then type AT+CMGF=1 it should respond with ok that indicates message format is text
Then type AT+CMGL="REC UNREAD" it should respond with OK
then send message to that sim from other source i have gone for way2sms GSM should respond in following way
It gives message location based on the location received type AT+CMGR=24 then you can retrieve that message
In that way GSM module can be configured to retrieve message
Same commands should be sent through UART program and display response on LCD module
GSM Program using LPC1343 download (with WDT)
download (with out wdt)
Successfully Implemented.
