Problem: The SIM900A network indicator light flashes slowly and flashes quickly.
　 Cause 1: The power supply to the module is not working! The power is not enough, even if the voltage is met, the current is not enough.
Solution: This kind of power supply can be realized by the voltage regulator module we gave, but it should be noted that the input of the voltage regulator module should be 9V 1A or more of the DC power supply, and the 4V obtained by adjusting the output of the voltage regulator module (recommended 4V, of course As long as the voltage range is met, the SIM900A module can be operated. If the input to the voltage regulator module is 5V or other DC power supply less than 9V, most of the SIM900A modules will not work properly.
　 Cause 2: The phone card may not be supported.
Solution: Can I use AT+CPIN? To detect if the phone card has been read. If there is an ERROR message indicating that the card may not be read, you can try another card. If you return READY, it means that you have read the card. At this time, it is most likely that you have not registered to the network. You can wait for a while and observe the status of the network light, or use AT+COPS? Instructions to detect whether it is registered to the network, if you return to China Mobile or China Unicom (English), it means that you have registered to the network.
Cause 3: The SIM card slot is loose, or the pins of the six SIM card holders are shorted.
Solution: You can use the soldering iron to iron the 6 pins of the SIM card holder, and let the loose pins connect, so that the short is disconnected.
Cause 4: The mobile phone card you are using has poor anti-interference ability and the antenna interferes with the SIM card.
Solution: Can I remove the GSM antenna and use AT+CPIN? To detect if the phone card has been read. If you return READY, it means you have read the card, then plug in the antenna, then use AT+CPIN? To detect if the phone card has been read. If you return ERROR, it means the antenna interferes with the card reading! The antenna can be kept as far as possible from the SIM card, or an SMA-to-SMA cable can be used to keep the GSM antenna away from the SIM card.
Frequently Asked Questions 2The brightness of the power light is not uniform, it will be brighter, and it will be darker. Call the calling card in the module, and the phone will hang up with a single or a few rings.
Solution: This kind of power supply can be realized by the voltage regulator module we gave, but it should be noted that the input of the voltage regulator module should be 9V 1A or more DC power, and the 4V obtained by adjusting the output of the voltage regulator module (recommended 4V, of course As long as the voltage range is met, the SIM900A module can be operated. If the input to the voltage regulator module is 5V or other DC power supply less than 9V, most of the SIM900A modules will not work properly. It is also possible to connect a diode in series with a 5V 2A power supply to make the voltage conform to the range of 3.5-4.5! If you are buying a SIM900A V4 voice version, you can directly connect the 5V 2A power supply to the corresponding pin!
FAQ 3Use the computer to debug the command, the serial port assistant does not return a value, or does not have the correct return value!
Solution: First check if the wiring is correct. The wiring part can refer to the module's typical interface documentation. The command sent is incorrect. Refer to the AT command or tutorial. The first instruction is not all capitalized! There is no carriage return after the instruction (the serial port assistant only needs to check the sending of a new line to add the carriage return after the command). Refer to the tutorial! The hardware or driver of the module that connects the module to the computer!
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