Design of Android audio accessories based on Freescale MCU and Audio Codec

Author: Freescale company Zhiyang Zhang, Javen Jiang, Weiping Liu, Oliver Chen

summary

The Android audio accessory is a new function in the Android Open Accessory (AOA) protocol 2.0. It outputs audio from Android devices to the accessory through the standard USB Audio Class Interface, and plays the audio through the accessory sound card; Interface devices to control Android devices, such as simple control of media playback. This article describes in detail the design scheme of Android audio accessories based on Freescale MCU and Audio CODEC.

Introduction to Freescale Android Audio Accessories

This Android audio accessory solution uses Freescale KineTIs K (Cortex-M4) series MCU MK70FN1M0VMJ12 as the main control chip, and Freescale's SGTL5000 audio codec outputs audio. MCU and Android devices receive raw audio data via USB and output to SGTL5000 audio codec via I2S. The following are the main features of Freescale Android audio accessories:

· Android device to accessories using 44.1KHz sampling rate, dual channel, 16-bit raw PCM audio input

· HID to achieve music device music track switching and pause control

Adjust the output volume of SGTL5000 through I2C

· Adopt SGTL5000 low power consumption high performance stereo output

· Xtrinsic Low-Power Touch-Sensing interface control input

1 Android audio accessory hardware introduction

1.1 Overall hardware structure

Hardware block diagram

Figure 1 Android audio accessory hardware block diagram

Figure 1 Android audio accessory hardware block diagram

Android audio accessory basic composition

Android audio accessory basic composition

1.2 Design of hardware function modules

Freescale KineTIs MCU MK70FN1M0VMJ12

Freescale KineTIs K series is a low-power, high-performance microcontroller based on ARM Cortex-M4. This solution uses the MK70FN1M0VMJ12 in this series for Android audio accessory design, with 1MB Flash and 128KB RAM capacity, and also has a USB 2.0 interface. Android audio accessories use the following MCU functions:

· MCU working rate 120 MHz

· Using USB Full Speed ​​as audio input

· Communicate audio signal with SGTL5000 CODEC through I2S audio interface

· Transmit control signal through I2C and CODEC communication

· Use Xtrinsic Low-Power Touch-Sensing Interface as media control input

Figure 2 Schematic diagram of Kinetis MCU

Figure 2 Schematic diagram of KineTIs MCU

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