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Questions Related to Audio

What are the reasons why modules fail to perform voice communication?
1) If AT+CPIN is used, check if the module recognizes the SIM card.
2) Check if the SIM card is working.
3) Check the working frequency band and working mode if you use AT + CBAND? and AT + CFUN?.
4) Check the RF signal quality with AT+CSQ.
5) Check if the RF antenna is properly connected.
6) It must be ended with ";". For example: ATDxxxxxx;
How do I perform an audio test (Loopback) to SIM900 modules in the production line?

Use the command: AT + AUTEST

For details, connect the SIMCom FAE team.

AT + AUTEST= <state><type>

Defined value:


0 - forbidden



0-normal audio channel

1-Aux audio channel

How do I switch audio channels?
Use AT+CHFA=1 (to switch to the auxiliary channel) and AT+CHFA=0 (to switch to the main channel)
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