Chinese information or related introduction of GSM module SIM900A

Hello, 1. Module AT command responds, but can't make a phone call/send a message?

A: There is a corresponding at command, which means that the module is already working, and you can't make phone calls/send text messages. This may be because there is a communication problem between the SIM card and the module (that is, the SIM card is in poor contact). In this case, please send: AT+CPIN? , instruction, inquiry, if the return is not ready, it means that the communication between SIM card and module is not normal. This problem is generally caused by poor contact between SIM card holder and SIM card. Solution: First, turn off the power supply of the module, take out the SIM card, wipe the six metal contact pins of the SIM card holder with gauze, and tilt these contact pins a little by the way, then install the SIM card and turn it on. Then send: AT+CPIN? Command to see if it returns to the ready state. You must return to the ready state before performing other operations (phone/SMS /GPRS, etc.). ).

Second, the IP mapping settings are incorrect.

This is mainly when using the router, it needs to be set (the computer is directly connected to the ADSL cat, and this setting is not needed), because the IP assigned to the computer by the router is a local area network IP, not a public network IP, so it is necessary to set forwarding rules for the router to forward the data of the public network IP to the designated computer IP, that is, the DMZ host setting. For example, my computer IP address is:192.168.106, then on the router settings page, select the forwarding rule DMZ host and set the DMZ host IP address as:192.166.