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Figure 29: RI behaviour of URC or receive SMS
However, if the module is used as caller, the RI will remain high. Please refer to the following figure.
Figure 30: RI behaviour as a caller
4.7. Audio Interfaces
SIM800H&SIM800L provides two analog inputs (MIC1P/1N; MIC2P/2N), which could be used for electret
microphone. The module also provides two analog outputs (SPK1P/1N; SPK2P/2N).
Table 13: Audio interface definition
Pin name
Pin number
Function
MIC1P
52
Main Audio
input positive
MIC1N
12
Main Audio input negative
SPK1P
53
Main
Audio output positive
Main
SPK1N
13
Main
Audio output negative
MIC2P
9
Secondary Audio input positive
MIC2N
10
Secondary Audio input negative
SPK2P
51
Secondary Audio output positive
Secondary
SPK2N
11
Secondary Audio output negative
SPK1P/1N output can directly drive 32Ω receiver, SIM800H&SIM800L internal has class-AB audio amplifier,
the following table is class-AB performance:
SIM800H&SIM800L_Hardware Design_V2.02 35
2015-07-27
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Table 14: Performance of audio amplifier
Conditions
Class-AB AMP
4.2V 8Ω THD+N=1%
0.87W
3.4V 8Ω THD+N=1%
0.53W
4.2V 8Ω THD+N=10%
1.08W
3.4V 8Ω THD+N=10%
0.65W
SPK2P/2N output can directly drive 8Ω speaker.
AT command “AT+CMIC” is used to adjust the input gain level of microphone. AT command “AT+SIDET”
is used to set the side-tone level. In addition, AT command “AT+CLVL” is used to adjust the output gain level.
For more details, please
refer to document [1].
In order to improve audio performance, the following reference circuits are recommended. The audio signals
have to be layout according to differential signal layout rules as shown in following figures.
