[SOLVED] Need a GSM module but don't know which to choose

I am working on some sort of security system project. I need a GSM modem for the purpose of sending/receiving text messages.

I haven't used any GSM modem yet so i don't know which one should i pick. Surfing the web gives me some models like SIM900/SIM900A/SIM900D & SIM-MINI. But i don't know whats the difference in them & which one should be chosen.
I kinda like the structure and price of SIMI.MINI https://digipak.org/zencart/index.php?main_page=product_info&cPath=5&products_id=197


P.S : I am using PIC 16/18f MCU
Any advice will be appreciated.

I highly recommend SIM800L. It's a new chip, small size and modules are available for RIDICULOUS price.

You can get prototype modules for 7€ on ebay.
https://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=sim800l&_sop=15

It works very well for basic operations such as text messages. SIM900 is of course okay too, but it's bit more bulkier.
There's plenty of GSM modules,(M590, TC35, Simcom), but they all work with AT commands just as well. Just pick one that fits your requirements. If no specific requirements(size, power consumption, features), pick the one that is cheapest. They all work.

Thanks for your kind reply.

1) Correct me if i am wrong ; It uses TTL pins so if i buy a USB-TO-TTL converter, then i can also connect this module to my Laptop.

2) Is their any AT-Command Simulator so that (for now) i don't use physical modem & i can get my hands on AT-Commands and their respective response.

tajiknomi said:

1) Correct me if i am wrong ; It uses TTL pins so if i buy a USB-TO-TTL converter, then i can also connect this module to my Laptop.

Click to expand...

Yes , you can do it ..
but check if your "TTL" level on GSM board is 5V , not 3,3 V ?
else you must have 5V tolerant input on RX GSM or add a level converter device . (or resistor divider!)

2) Is their any AT-Command Simulator so that (for now) i don't use physical modem & i can get my hands
on AT-Commands and their respective response.

Click to expand...

you can use Terminal VBray + Macro .
set Macro to put AT command on each of 12 touch..
or similar program as serial terminal software REALTERM

**broken link removed** , i used to test a GSM2-click from MikroE

but you must before apply a correct sequence of power ON ..
i did it with a PIC program wich has a debug mode :
When in debug mode, the the PIC receive direct AT command from a terminal
and send this command to the GSM, and write the response back to terminal display.

on every GSM .. you must get a "OK" response when first transmit "AT" or "AT"<CR>
if not, no chance to dialogue with GSM.

paulfjujo said:

you can use Terminal VBray + Macro .
set Macro to put AT command on each of 12 touch..
or similar program as serial terminal software REALTERM

**broken link removed** , i used to test a GSM2-click from MikroE

but you must before apply a correct sequence of power ON ..
i did it with a PIC program wich has a debug mode :
When in debug mode, the the PIC receive direct AT command from a terminal
and send this command to the GSM, and write the response back to terminal display.

on every GSM .. you must get a "OK" response when first transmit "AT" or "AT"<CR>
if not, no chance to dialogue with GSM.

Click to expand...

I have used Realterm for serial communication but i really don't get the Software/utility which can Execute & respond me like Physical modem

hello,


if i get a right understanding, you want un GSM Simulator program ?
I don't know if this kind of software exist..

but you can use a litle PIC as a PIC12F1840 (DIP 8) to write a program
wich can simulate a GSM ..

handle the UART
receive the AT command
handle delais for feeback
Answer with appropriate message (stored in EEPROM or Flash)

tajiknomi said:

1) Correct me if i am wrong ; It uses TTL pins so if i buy a USB-TO-TTL converter, then i can also connect this module to my Laptop.

Click to expand...

SIM800L UART(serial) level is 2.8V. You can see all the information you need from SIM800L datasheet.

There are boards with on-board 5V->2.8V TTL conversion for 10€, for example here:
https://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=sim800l+5v&_sop=15

tajiknomi said:

2) Is their any AT-Command Simulator so that (for now) i don't use physical modem & i can get my hands on AT-Commands and their respective response.

Click to expand...

I don't think there is hardware simulator. You can see all the responses from the chip's AT command manual(just google it).

There is AT command tool though(that you have to use with the physical modem):
https://m2msupport.net/m2msupport/module-tester/

It is Java based, so you have to circumvent the security check to use it.
You can also do commands manually using Terminal, PuTTy, RealTerm etc.