Car bluetooth phone technology

Research and Implementation of Car Bluetooth Telephone Technology

The car bluetooth phone is specially designed for driving safety and comfort. Users only need to have a mobile phone with bluetooth function to connect with the car bluetooth, so as to make calls through the car equipment. Users do not need to touch the mobile phone to control the mobile phone, use voice commands to control, operate the vehicle terminal or even the steering wheel to answer or make calls, and make calls through the car audio or Bluetooth wireless headset, which can ensure a good call effect. Car bluetooth phones are generally used in front-mounted car entertainment terminals and rear-mounted car devices, and it is an applicable technology. This paper mainly introduces the realization principle of the Bluetooth phone function of the vehicle-mounted device based on the Android system.

1. Bluetooth architecture of Android system

Android system Bluetooth includes application layer, framework layer and local library, HAL layer and Kernel kernel driver code. The BlueZ protocol is mainly implemented in the local library and kernel code, and the local library and kernel communicate through the HAL layer interface. The framework layer mainly implements the management of the Bluetooth application protocol Profile, and interacts with the local library through the JNI interface. The framework layer includes local Bluetooth device adaptation, local Bluetooth information and management, remote device attributes, RFCOMM-based Bluetooth device server and client socket management, various Bluetooth profile services, etc. The modules that manage Bluetooth phone functions include SettingsApp, Phone, and Bluetooth. It is mainly the Android system of the vehicle-mounted smart device that supports the Bluetooth HFP protocol (Hands-freeProfile). HFP can realize the phone control function based on the Bluetooth connection, and provide a unified standard for the Bluetooth phone function.

2. Realization of Bluetooth phone in Android system

2.1 Bluetooth HFP protocol

The HFP protocol defines two roles: the audio gateway (AG) and the hands-free component (HF): the AG device is used as the audio input/output gateway, that is, the mobile phone terminal; the HF device is used as the remote audio input and output mechanism of the audio gateway, that is, the vehicle device end. The HFP protocol provides a number of telephone-related remote control functions for HF devices. First, establish RFCOMM connections, and exchange AT commands between the two devices through the RFCOMM protocol channel. The AT command set is based on ITUTV. 250 and GSM07.07. The HF end sends AT commands to read the AG end status and control the AG end phone functions. At the same time, the AG side indicates the status of the terminal through the AT command (+CIEV:).

2.2 Realization of Android system HF protocol

The AG side of the Android system HFP protocol receives and parses the call-related AT commands and processes the calls to the phone system interface. AT commands include:

"AT+D" dialing operation; "AT+A" answering operation; "AT+CHUP" hanging up operation; "AT+CLCC" call status query; "AT+VTS" dual-tone multi-frequency tone sending; "Call hold operation; "AT+VGS" speaker volume adjustment; "AT+VGM" microphone volume adjustment; "+CIND" mobile phone status indication, etc.

It meets all the phone control functions of the HF end. Therefore, the Android system mobile phone supports the AG-side Bluetooth headset and Bluetooth phone functions, and the HF-side vehicle equipment should also have equivalent functions. The vehicle device side needs to increase the interface interaction and logic processing of the Bluetooth phone, and support the processing flow of the HF side of the HFP protocol.

The framework layer (Framework) above Android 5.0 adds hands-free service client management and improves the HFP protocol process processing, so the vehicle-mounted equipment using Android 5.0 and above systems can provide complete Bluetooth phone functions on the basis of the existing framework. The specific implementation process is shown in Figure 1.

BluetoothClientService adds phone control-related interfaces, including dial0, acceptCall(), holdCall0, terminateCall(), holdcau0, getCurrentCalls0, etc., providing functions such as dialing, answering, hanging up, holding, and call status query. HeadsetClientStateMachine, as a bridge between the framework layer and protocol processing, mainly completes the logic processing and state jump of HFP in the framework layer, including the following two aspects: (1) Receive phone instructions from the local protocol layer module, and notify the application through system broadcast The program rings or updates the call status display. (2) Manage the status of the protocol (connected or disconnected), call this interface, and send the control of the application to the protocol module. In the Bluetooth protocol layer, Bta-hf-client-cmd is responsible for the assembly and transmission of AT commands, and Bta_hfclient is responsible for the reception, analysis and reporting of AT commands. The Bluetooth phone APP is mainly responsible for UI interaction and interface logic processing, and provides users with convenient functions, including dial pad, synchronous address book and call records, search contacts, call reminders, buttons on the call interface, etc. If a phone function button is added to the steering wheel, the button event of the steering wheel is sent to the vehicle-mounted device through the vehicle wiring harness, and functions such as calling, answering, and hanging up can be triggered, so that the driver can control the mobile phone without leaving the steering wheel. .

Summarize

At present, Bluetooth devices are widely used, and the Bluetooth protocol is relatively mature. It is a form of vehicle interconnection to transfer the functions of mobile phones to vehicle-mounted devices through Bluetooth connections. The purpose is to facilitate driving and improve user experience. With the development of hardware and software technology, more electronic products based on Bluetooth connection solutions will be applied to vehicle, medical and health fields, providing users with more convenience.

The above is the research and implementation method of the car Bluetooth phone technology introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have Bluetooth product design and development needs, you can trust us. We have rich experience in custom development of smart electronic products. We can evaluate the development cycle and IC price as soon as possible, and can also calculate the PCBA quotation. We are a number of chip agents at home and abroad: Songhan, Yingguang, Jieli, Ankai, Quanzhi, realtek, with MCU, voice IC, BLE Bluetooth IC, dual-mode Bluetooth module, wifi module. We have hardware design and software development capabilities. Covering circuit design, PCB design, single-chip microcomputer development, software custom development, APP custom development, WeChat official account development, voice recognition technology, Bluetooth development, wifi technology, etc. It can also undertake the research and development of smart electronic products, the design of household appliances, the development of beauty equipment, the development of Internet of Things applications, the design of smart home solutions, the development of TWS earphones, the development of Bluetooth earphone speakers, the development of children's toys, and the research and development of electronic education products.