Gpio; Audio Interfaces - SimCom SIM900 Reference Design Manual

SIM900 Reference Design Guide Notes
VBAT
510R
NETLIGH
4.7K
BC847
T
47K
Figure 8: NETLIGHT indicator

2.3.2 GPIO

SIM900 serves 12 GPIO which can be controlled by the customer. As a GPI, the status can be read
by the AT command and as a GPO, it also can be controlled by the AT command. The customer
can use this GPIO to achieve some simple control. For more detail, please refer to Document[1].

2.4 Audio interfaces

SIM900 provides a pair of differential analogy audio channel, MICP & MICN can be connected to
an electret condenser microphone directly and SPKP & SPKN can drive a 32 Ohm speaker. The
maximum output power is 96mW. If the speaker is 8 Ohm, you should add an audio amplifier
between the module output and the speaker. We recommend National Semiconductor's LM4890.
Also, the microphone input channel can be configured to a single ended mode. In this mode, the
MICN can be left open. The negative terminal of the microphone can be connected to GND in the
customer's board.
For adjustment, you can use AT+CMIC to set the input gain level of microphone, AT+CLVL to
change the volume of the speaker. For details, please refer to [2].
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SIM900_AN_Reference Design Guide_V1.01 01.27.2010