With the popularity of family cars, people's time in the car has increased significantly, and in-car calls are inevitable. For driving safety, Bluetooth hands-free calling is a good solution, and the car Bluetooth system has been greatly developed. But taking into account user privacy requirements. Sometimes private calls are still needed. For some users who drive a lot but prefer headphones, Bluetooth headsets are not a perfect solution. Because most of the current Bluetooth mobile phones on the market cannot support two Bluetooth hands-free devices at the same time, that is, the mobile phone connects the Bluetooth headset and the Bluetooth device at the same time through the Bluetooth hands-free protocol.
Therefore, this special scenario for in-vehicle applications. The car wireless RF headset system is a good solution. The existing earphones can't interact with the sound, especially when listening to the sound while listening to the sound and using the earphone to answer the phone, which is more unfavorable for driving safety. During the call using the car Bluetooth hands-free phone, after the RF headset leaves the base, the voice of the call is transferred to the headset, and the speaker inside the car no longer sounds. When the call is over, you can use the steering wheel button or the car phone operator interface to hang up the phone. But before putting the headset back in the base. The vehicle's audio is also output from the headphones. When the user puts back the headset. Audio recovery is output from the original speakers.
The design and functional characteristics of the system will be discussed in detail.
1 RF technology
The in-vehicle wireless RF headphone system introduced in this paper uses radio frequency technology. Before introducing this solution, the radio frequency technology involved in the article will be explained.
Radio Frequency (RF), which represents the electromagnetic frequency that can be radiated into space, and the frequency range is between 300 kHz and 30 GHz. The essence of radio frequency is the radio frequency current, which is an abbreviation of high frequency alternating current electromagnetic wave. An alternating current that changes less than l000 times per second is called a low-frequency current, and a frequency of more than 10,000 times is called a high-frequency current, and a radio frequency is such a high-frequency current. As a new generation of short-range wireless data communication technology, RF technology has the advantages of small size, low power consumption, stable performance and strong anti-interference ability. And it is suitable for forming a small communication local area network, so it has been widely applied and researched in the industrial and civil fields.
In recent years. At the same time as the development of wireless communication technology, the production process and level of large-scale integrated circuits, digital technologies and circuit systems are becoming more and more mature. This allows most of the functions of the wireless communication system to be integrated into the interior of a small chip. Take the short-range wireless communication system as an example. Only need to use short-range wireless RF transceiver chip. Coupled with a microcontroller with control function and a small number of peripheral devices, a communication module with wireless transmission function can be constructed.
In this small system, devices such as capacitors, inductors, and crystal oscillators are integrated inside the chip, which has good versatility and strong anti-interference ability. Not susceptible to environmental changes. The RF transceiver chip can adopt various modulation methods based on the FSK modulation method. Generally working in the ISM common frequency band, no additional application for the communication channel is required, and the operation is simple and convenient.
Inside the communication module, there is already a data transmission protocol that is generally required to transmit data or an encryption protocol used to enhance confidentiality, and it is as simple and transparent as possible. All operating parameters such as transmit power and operating frequency can be set by software, which reduces the user's requirements for the principle of wireless communication and the working mechanism, making the application process easier. In general, the user can implement the basic wireless transmission function by operating the specific control register according to the command word.
This type of short-range wireless data communication system is small in size, low in power consumption, good in stability, strong in anti-interference ability, simple in development, easy to maintain, and can be embedded in various other devices. A wireless connection between devices is achieved. Complete different functional integrations.
Due to the variety and number of different types of wireless transceiver chips in different companies, the choice of wireless transceiver chips is crucial in the design. The right choices can reduce development difficulty, shorten development cycles, reduce costs, and bring products to market faster. The following factors should be considered when selecting a wireless transceiver chip: power consumption, transmission power, receiving sensitivity, number of peripheral components required for transceiver chips, and chip cost.
The solution uses the sturdy CC85XX device family, which provides a low-cost, single-chip solution for powerful, high-quality, short-range 2.4 GHz wireless digital audio streams. Two or more devices form a PurePath wireless audio network, and by taking care to ensure that the audio network can provide seamless and powerful audio streams in different environments, it can work with existing wireless technologies. Friendly coexistence in the crowded 2.4 GHz ISM band.
Simply connect the CC85XX to an external audio source or sink (eg audio codec, S/PDIF interface or Class D amplifier) ​​and several buttons, switches or LEDs for human interaction, which can be achieved without any software development. Most applications. The control of the external audio device is based on I2C or G10. Includes local or remote volume control. Advanced applications can be directly connected to the host processor or DSP with CC85XX and streaming audio, while also controlling all aspects of device and audio network operations.
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