Hardware Design V1.01(091226)
Table Of Contents
- Contents
- Version history
- 1 Introduction
- 2 SIM900 Overview
- 3 Application Interface
- 3.1 SIM900 Pin Description
- 3.2 Operating Modes
- 3.3 Power Supply
- 3.4 Power Up and Power Down Scenarios
- 3.5 Power Saving
- 3.6 Summary of State Transitions (except SLEEP mode)
- 3.7 RTC Backup
- 3.8 Serial Interfaces
- 3.9 Audio Interfaces
- 3.10 SIM Card Interface
- 3.11 LCD Display Interface
- 3.12 Keypad Interface
- 3.13 ADC
- 3.14 Behaviors of the RI
- 3.15 Network Status Indication
- 3.16 General Purpose Input Output (GPIO)
- 3.17 External Reset
- 3.18 PWM
- 3.19 I2C Bus
- 4 Antenna Interface
- 5 Electrical, Reliability and Radio Characteristics
- 6 Mechanics
SIM900 Hardware Design
3.9 Audio Interfaces
Table 9: Pin define of the Audio interface
Pin Name Pin Number Function
MIC_P 19 Microphone1 input +
MIC_N 20 Microphone1 input -
SPK_P 21 Audio1 output+
AIN/AOUT
SPK_N 22 Audio1 output-
LINEIN_R 23 Right Channel input
LINE IN
LINEIN_L 24 Lift Channel input
The module provides one analog input channel, AIN, which may be used for microphone. The electret
microphone is recommended when the interface is used for microphone. The outputs connect to the receiver. The
receiver outputs only can directly drive 32Ω.
External line inputs are available to directly mix or multiplex externally generated analog signals such as
polyphonic tones from an external melody IC or music generated by an FM tuner IC or module.
You can use AT+CMIC to adjust the input gain level of microphone, use AT+SIDET to set the side-tone level. In
addition, you can also use AT+CLVL to adjust the output gain level. For more details, please refer to document
[1].
It is suggested that you adopt one of the following two matching circuits in order to improve audio performance.
The difference audio signals have to be layout according to difference signal layout rules. As show in following
figures (Note: all components package are 0603.) If you want to adopt an amplifier circuit for audio, we
recommend National Company’s LM4890. Of course you can select it according to your requirement.
3.9.1 Speaker Interface Configuration
Figure 23: Speaker interface configuration
SIM900_HD_V1.01 26.12.2009
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