I do have some doubts about the communication of the SIM900 GSM module with the PC. By default the GSM module has the RS232 connection to interface with PC.

This has Tx and RX as shown source:link

But my PC has only USB connection . So do I really need a USB to RS232 connector for interacting with PC , something like

USB to RS232


CAN I COMMUNICATE the SIM900 module from the PC using the TTL by using a USB to TTL converter and connected to the Rx/Tx pin of the GSM module using something like this?

enter image description here


RS232 is a different voltage level, as well as inverted from the logic-level ("TTL") UART signals. You need the RS232-to-USB adapter you showed in the second photo.

I'm retracting this comment as I didn't notice the pads on the bottom edge of the board. However, without a schematic for the board, I cannot be sure what those are connected to.

If we assume these are directly connected to the TTL-level UART pins of the module, there is still a problem. These will also be connected to the RS232 level converter (which I assume is on the bottom of the board since I don't see it). The module's RX pin will be actively driven by the level converter and it will not work to directly connect your UART to that pin (and, in fact, may damage it). You'll need to find a jumper to disconnect the converter chip or desolder it.

You need to contact your Ebay seller to see if he con provide this information.

  • \$\begingroup\$ So even if I use the Tx/Rx of the USB to TLL converter to the Rx/Tx of the GSM , will it not work ? \$\endgroup\$ – rahulmr Mar 24 '15 at 11:01

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