Wireless Notice Board

Well I just loved the idea of a wireless notice board which will display the notice whenever some SMS is sent to it. That way you can intimate the concerned people about the notice or information even if you are not physically present at the location. This can be used in colleges wherein two notice boards can be installed per department. One will be used by the principal and the other may be by the head of dept. or the teachers.

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Step 1: SIM 300/900 module

Introduction

SIM 300 is a GSM modem with a simple serial interface. SIM 300 modem can accept any GSM network operator SIM card and act just like a mobile phone with its own unique phone number. With this module one can send/receive sms, connect to internet via GPRS and receive calls. The modem can either be connected to PC serial port directly or to any microcontroller. When purchasing purchase the entire board. As it comes with RS232 to TTL converter and ethernet port. Also do check the module by calling a few times when in the shop.

You can purchase this module online. Some of the sites are listed below: 

There are two LEDs on the board. One is power LED and the other is the network LED. When you insert your SIM card into the slot and power ON the device the power LED will be turned ON. After few seconds the network LED will start blinking after an interval of 3 seconds. If this happens it means signal is proper but if it is blinking faster it means that there is no network. If your mobile phone has network then this module should have network at the same location(provided the antenna is connected.) Make a call and it should ring. Do it a couple of times before purchasing from a store.

AT commands

These are the Haye’s command set also called AT commands. AT stands for attention. These commands are used to control the modem. Using these commands the modem can be operated. There are different commands for sending/reading sms etc. For further information about the history you can read the Wikipedia article.

The AT command set can be downloaded here.

The table in the image lists few of the commands. The most basic command is AT and the response is OK. If you get OK then it means that everything is working fine.

Now to test out the commands or for direct interfacing with the PC or laptop you can use USB to RS232 adapter. You will need to install prolific drivers. These will be included in a small CD that accompanies the adapter or you can download here.

Once you do that there will be a COM port available now. Some of the basic commands are explained in the following video.

Step 2: Components and Connections

1. Micro-controller board with at least two hardware UARTs(not mandatory but will be beneficial.)
2. SIM 300 module or equivalent(with the charger etc.)
3. Some display e.g. LCD, dot matrix, graphical LCD etc.

The connection diagram is the image 1 and the launchpad pins are given in the image 2. Note that the code is written in Energia which can be used with Arduino boards as well.

Step 3: Code Explanation

The main objective is to extract the message from the received message. Now you can use some special character for this but I’ve decided to use the concepts of html tags. So my tag is . Whatever is written in these tags will be displayed. String object provides beautiful string manipulation functions. So we will not reinvent the wheel but use it in our application so to speak. Let’s look at the code that will extract the message from the received data.

char buffer[250];Serial.readBytes(buffer, 250);
String message = buffer;
String command = "<s>";
String commandEnd ="</s>";
int indexOfMessage = message.indexOf(command);
int indexOfMessageEnd = message.indexOf(commandEnd);
if(indexOfMessage>0 && indexOfMessageEnd>0){
String actualMessage = message.substring(indexOfMessage+3,indexOfMessageEnd);
Serial.print("Message             :");
Serial.println(message);
Serial.print("Command             :");
Serial.println(command);
Serial.print("CommandEnd          :");
Serial.println(commandEnd);
Serial.print("Actual Message      :");
Serial.println(actualMessage);
actualMessage.toCharArray(actualMessageArray,250);

We are making two strings command and commandEnd. These will store our tags. Next we need to find the index of these tags. For this we use indexOf() and this will return –1 if the string is not present. So we need to send the message only if both the indices are not –1. Next is just one toCharArray(), this is for the LCD function. Also the serial printing is just for our reference. You may remove those lines. The scrolling part is taken from arduino cook book. Here is the link. Thank you for reading this. If you liked this post do share it with others!! For more projects and tutorials visit my blog.

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Step 4: Entire Code

#include <LiquidCrystal.h>;
LiquidCrystal lcd(42,44,49,50,70, 69);
 
const int numRows = 2;
const int numCols = 16;
char actualMessageArray[250];
 
void setup()
{
      // put your setup code here, to run once:
      Serial.begin(9600);
      Serial7.begin(9600);
      Serial7.println("AT");
      while(Serial.available()>0)
      {
        Serial.print((char)Serial.read());
      }
      delay(1000);
      Serial7.println("AT+CMGF=1");
      while(Serial.available()>0)
      {
        Serial.print((char)Serial.read());
      }
      delay(1000);
      Serial7.println("AT+CNMI=2,2,0,0");
      delay(100);
      while(Serial.available()>0)
      {
        Serial.print((char)Serial.read());
      }
      delay(1000);
      lcd.begin(numCols, numRows);
      lcd.setCursor(0,0);
}
 
void loop()
{
  // put your main code here, to run repeatedly:
 if(Serial.available()>0)
 {
      char buffer[250];
      Serial.readBytes(buffer, 250);
      String message = buffer;
      String command = "<s>";
      String commandEnd = "</s>";
      int indexOfMessage = message.indexOf(command);
      int indexOfMessageEnd = message.indexOf(commandEnd);
      if(indexOfMessage>0 && indexOfMessageEnd>0){
      String actualMessage = message.substring(indexOfMessage+3,indexOfMessageEnd);
      Serial.print("message          :");
      Serial.println(message);
      Serial.print("command          :");
      Serial.println(command);
      Serial.print("commandEnd       :");
      Serial.println(commandEnd);
      Serial.print("actualMessage    :");
      Serial.println(actualMessage);
      actualMessage.toCharArray(actualMessageArray,250);
     }
 }
  marquee(actualMessageArray);
  delay(1000);
  lcd.clear();
}
void marquee( char *text)
{
    int length = strlen(text); // the number of characters in the text
    if(length < numCols)
    lcd.print(text);
    else
    {
        int pos;
        for( pos = 0; pos <= numCols; pos++)
        lcd.print(text[pos]);
        delay(1000); // allow time to read the first line before scrolling
        pos=1;
        while(pos <= length - numCols)
        {
        lcd.setCursor(0,0);
        for( int i=0; i < numCols; i++)
        lcd.print(text[pos+i]);
        delay(300);
        pos = pos + 1;
        }
    }
}

Step 5: Serial Monitor Output

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