SIM900 or SIM900 beginner questions

Going to the development of this GSM module and I have a few questions

1. SIM900/SIM900a
There are other differences between SIM900 and SIM900 than a lack of support bands 850 and 1900 MHz?
I'm from EU so I do not use 850MHz, the taking but there are other reasons to choose SIM900?

2. Firmware
I do not understand the logic of numbering firmware, how do I know which is the latest?
For examples: **broken link removed** fw for SIM900A
1137B13SIM900A64_ST_DL.rar but latest is write at 1137B03SIM900A64_ST_ENHANCE.cla
B03<B13 ????

3. Logic translation
It is required for use with 3.3V logic voltage levels for transmission RX, TX and RI?

4. Sample project
Recommend sample projects, ideally with MCU STM32Fxxx

5.Treatment with audio port
I would like SPK and MIC I / O used as a Line IN and Line Out for connection of audio I / O, seeking a sample solution with the protection and amplifier / buffer

6. Communication with the MCU
How to solve the communication with the MCU?
So far, it seems to me that it is sufficient to
RX / TX in USART,
REST for reset SIM900
RI for wakeup MCU if SIM900 recieve SMS or caal.
Add you recommend one of the other signal?

2. Firmware
I do not understand the logic of numbering firmware, how do I know which is the latest?
For examples: Her fw for SIM900A
1137B13SIM900A64_ST_DL.rar but latest is write at 1137B03SIM900A64_ST_ENHANCE.cla
B03<B13 ????

Click to expand...

Consult with your seller regarding firmware details.

3. Logic translation
It is required for use with 3.3V logic voltage levels for transmission RX, TX and RI?

Click to expand...

If you use uC, you can connect TX, RX pin of uC to RX, TX of SIM900 or any GSM Module. If you connect GSM Module from PC, you have to use serial converter (like MAX232 uC is higher voltage you have to use

4. Sample project
Recommend sample projects, ideally with MCU STM32Fxxx

Click to expand...

You have to tell what type of uC you are going to use and which language you knew, etc. Than only anyone can help. You can google "GSM Module and Microcontroller", etc. You can see many projects even on this edaboard forum (some of my own projects)

5.Treatment with audio port
I would like SPK and MIC I / O used as a Line IN and Line Out for connection of audio I / O, seeking a sample solution with the protection and amplifier / buffer

Click to expand...

Consult the respective datasheet. There is sample circuit for SPK and MIC also. Simple circuit.

6. Communication with the MCU
How to solve the communication with the MCU?
So far, it seems to me that it is sufficient to
RX / TX in USART,
REST for reset SIM900
RI for wakeup MCU if SIM900 recieve SMS or caal.

Click to expand...

Correct. I already mentioned in my 1st point. Just connect (shorting) GSM Module's RTS & CTS pins. Connect RX and TX pin of GSM Module to TX and RX pin of uC. Thats it.

thanks for the reply.

3. Logic translation

Click to expand...

With MCU
SIM900 use logic stretch with VDD_Ext 2,7V and MCU have logic 3.3V
For example RXD on SIM900 is pul up over resistor from VDD_EXT.
I never finished reading that can connect to RXD SIM900 with TX pin of the MCU (3,3V Logic)?

Consult with your seller regarding firmware details.

Click to expand...

My suplier speaking only chines :laugh:

SIM900 use logic stretch with VDD_Ext 2,7V and MCU have logic 3.3V
For example RXD on SIM900 is pul up over resistor from VDD_EXT.
I never finished reading that can connect to RXD SIM900 with TX pin of the MCU (3,3V Logic)?

Click to expand...

yes. you are right. abs max voltage is 3.1v on all digital pins. But I have connected 3.3v uC directly and works fine till date last 3 years back.

Hi Astrid,

1. SIM900/SIM900a
There are other differences between SIM900 and SIM900 than a lack of support bands 850 and 1900 MHz?
I'm from EU so I do not use 850MHz, the taking but there are other reasons to choose SIM900?

Click to expand...

The SIM900A is also band locked for Asian Countries ONLY

3. Logic translation
It is required for use with 3.3V logic voltage levels for transmission RX, TX and RI?

Click to expand...

The logic level High for the serial pins 2.8 volts (VDD_EXT), the RX pin input maximum is 3 volts. I would suggest a resistor divider for the RX input if your MCU is powered from 3.3 volts.


Cheers.

Batang said:

Hi Astrid,
The SIM900A is also band locked for Asian Countries ONLY

Click to expand...

Are you sure?
I know that there

but it is probably only a matter of some firmwares. SIM900A is dualband 900 amd 1800 MHz and EU use this frequency,
SIM900 add support for 850 and 1900 MHz and this band is not used in EU. 850/1900 is used in South America (Bolivis, Peru, Brazili, El Salvador etc.)