Fifth day, Wednesday (11/07/2012)

Assalamualaikum and peace everyone who still follow my blog. I’m gladly still health and can continue my work, so thankfully to my god that give me healthy body. From my last task in previous day, my supervisor has ordered to understand about AT command in GSM Modem. So today they have given GSM Modem to me to try it out. 3 people are in charges and they are Rahmah, Syuhada and included with myself. The tasks are sending SMS and receive SMS. For the future task, we need to combined with programmable PIC to send the information to the owner by SMS and owner can control the circuit by send SMS back and the PIC will execute what been ordered by owner.

Before we go through more, there a theory that must to know it. Global System for Mobile Communications (GSM) is a technology for second generation (2G) digital cellular networks which is a replacement for first generation (1G) analog cellular. It described a digital, circuit switched network optimized for full duplex voice telephony. The modem is a device that modulates an analog carrier signal to encode digital information and also demodulates such a carrier signal to decode the transmitted information. Modem is attached to computers for ‘dial-up’ to connect with other computer systems.

GSM modem is a specialized type of modem that operates over subscription based wireless network which is similar to a mobile phone. It accepts a SIM card and basically acts like a mobile phone for the computer. Similar to modem operations except that it sends and receives data through radio waves rather than a telephone line.

Sending SMS

1.      Insert the valid SIM card into the SIM slot.

2.      Connect the GSM Modem to the supplied AC-DC adapter and also to the serial port of the PC.

3.      Select the correct COM Port in Hyper Terminal and set up the parameters as follows.

4.      Power on the GSM Modem and wait for it to initialize. While waiting, we can use the following command to make sure we can communicate with the GSM Modem.

AT <ENTER>

 

The GSM Modem should respond with “OK”.

5.      Once it’s ready, the following response will be received from the modem.

Call Ready

 

6.      Now we can start sending the AT command to the GSM Modem. Start by configure the modem to use Text Mode instead of PDU mode for the SMS. This mode allows us to send SMS using AT commands without the need to encode the binary PDU field of the SMS. Use the following command to put the modem in text mode and it should respond with “OK”.

AT+CMGF=1<ENTER>

7.      After that, we can send the SMS message with the following command:-

AT+CMGF=”0135219644” <ENTER>

        Replace the above phone number with your own number. The modem will respond with:-

>

        We can now type the message and send the message using the <CTRL+Z> key.

>TEST <CTRL+Z>

After few seconds, the modem will respond with the message ID of the message, indicating that the message has been sent correctly.

+CMGS: 49

  

AT COMMANDS TO SEND A SMS

TEXT THAT RECEIVE FROM MOBILE PHONE

Receiving SMS

1.      Set up the GSM Modem following step 1 – 6 in the previous section.

2.      Once the GSM Modem is ready, we can use a mobile phone to send a SMS to the modem.

3.      The following response received from the modem indicates a new SMS is received.

 +CMTI:"SM",1

The last character indicates the memory index number, we use this index to read or delete this message. In this case, the index number is 1.

4.      To list out all the available SMS in the SIM card, we can use the following command: 

 AT+CMGL="ALL"<ENTER>
              And the modem will respond with a list of SMS messages in the SIM card. 

                                     LIST SMS MESSAGE IN SIM CARD

 PROBLEM STATEMENT

 During the experiment we got a few problem such as:

1. After select the correct COM Port in Hyper Terminal and set up the parameters, then we need to power on GSM modem. This activity should be repeated when to send or receive SMS. If we just let the modem power on, we can't get CALL READY. So, my opinion it harasses jobs to do.
2. First experiment in sending SMS, we got an error occur like below: 

 it show that +CMS ERROR : 515. From the action has been taken, we try another laptop to test the GSM modem and try to change the SIM card. Finally, after a few laptop been test, we got to send SMS. After we analyze the problem, we need to push the  <CTRL+Z> key many time so they will appear +CMGS: 49

  

  From what we done today, we know the function of GSM Modem in sending and receive SMS. we also know to use the AT command for this operation.