SIM900A, CP2102 and PuTTY



Connection Diagram:


There are separate RX and TX ports for 5V and 3.3V devices. Use middle RX and TX ports on 6 pin header which are for 5V device. RX from SIM900A goes to TX of USB to TTL adapter and vice versa. After connecting SIM900A Mini according to diagram perform the following steps.

  • Open up PuTTY
  • Choose Serial
  • Choose Serial line e.g. COM1 (Refer Control Panel>All Control Panel Items>System>Device Manager>Ports)
  • Speed or Baud Rate should be 9600
  • Click open wait few seconds


Now We have connected SIM900A module to our PC. Let’s test of module by using AT commands. Here is list of few commands to testing purpose.

Commands Description
AT Check connection between module and serial monitor
AT+CPIN? Check sim card status
AT+CSQ Check signal quality
AT+CGMI Check the module maker
AT+CGMM Check the module model type
AT+CGSN Check the module IMEI
AT+CMGR Read message, for exmple, AT+CMGR=1 to read message at position 1



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