Design and implementation of wireless headset based on nRF24E1

0 Introduction

At present, with the popularity of the Internet and personal computers, people usually use wired headsets for voice chat. Due to the limitations of wired headsets, people have to sit in front of the computer to chat.

If it takes a long time, it will cause the computer to radiate to the human body, thus affecting people's health; in terms of home television, people usually use the built-in speakers of the TV to listen to the sound from the TV, which sometimes affects the work and rest of other family members.

Based on these problems, this paper designs and implements a wireless headset based on nRF24E1. This design has the advantages of strong anti-interference ability, good confidentiality, good sound quality, and low cost. Its indoor transmission distance is about 30 meters, thereby reducing the radiation of the computer to the human body and does not affect the rest and work of other family members.

The wireless headset uses the most advanced wireless transceiver chip nRF24E1, which can realize wireless voice communication in the world's public ISM frequency band 2. 4G ~ 2. 5GHZ.

1 Introduction to nRF24E1

The nRF24E1 chip is a wireless transceiver module with a 2.4GHz wireless transceiver nRF2401 and an enhanced 8051 core launched by Nordic integrated circuit company NORD IC. The channel operation time of this chip is less than 200us, the data rate is 1Mbps, and no external SAW filter is required. It is currently the world's first low-cost RF system-level chip that is universal and universal. It is embedded with a microprocessor compatible with 8051 and a 10-bit 9-input analog/digital converter, which can work stably at a voltage between 1.9V and 3.6V; it also has a voltage regulator and a VDD voltage monitor. The wireless transceiver part has the same function as nRF2401, which is started by the internal parallel port and the internal SPI. Each signal to be sent can be programmed as an interrupt for the processor, or transmitted to the microprocessor through the GPIO port. The nRF24E1 chip can realize wireless communication in the world's public ISM (Industrial, Scientific and Medical) frequency band of 2.4 ~ 2.5GHz. The transceiver part includes a frequency divider, an amplifier, a regulator and two transceiver units. The output energy, frequency band and other RF parameters can be easily programmed and adjusted through the RF register. In the sending mode, the current consumption is only 10.5mA; in the receiving mode, the current consumption is only 18mA, so the power consumption is quite low.

2 Hardware structure design of wireless headset

The wireless headset is mainly composed of a plug part and a headset part. The plug part is mainly composed of two plugs and nRF24E1. The two plugs are a microphone plug and a headphone plug, which are respectively plugged into the microphone jack and the headphone jack of the computer or the headphone jack of the home TV; the headset part is mainly composed of a microphone, a headphone and nRF24E1. Its hardware structure block diagram is shown in Figure 1. The wireless headset realizes two-way voice communication through the wireless voice transceiver chip nRF24E1.

The wireless headset can send the voice of a person to the computer through the microphone; it can also send the sound of the computer or TV to the headset of the wireless headset. Whether it is sending the voice to the computer or TV, or sending the voice to the headset, the working principle of one-way voice transmission is the same. Figure 1 Hardware structure block diagram of wireless headset nRF24E1 chip has a 9-channel 10-bit ADC (Analog to Digital Converter), and its sampling frequency is 24 bytes or 3ms of audio sampling signal per RF (Radio Frequency) data packet. The sending and receiving process of wireless headset sending human voice to computer or TV is shown in Figure 2: The circuit diagram of the sending end is shown in Figure 3. There needs to be a pre-filter amplifier circuit between the microphone and the ADC module of nRF2401. It filters and amplifies the analog audio signal picked up by the microphone. The amplified analog audio signal is sent to the ADC. Figure 2 One-way voice transmission and reception process Figure 3 Voice transmission circuit diagram At the receiving end, when the RF front-end nRF2401 receives a valid data packet and the microcontroller receives an RF reception interrupt, the valid data portion of the received data packet can be separated out by the FIFO of the RF front-end; then, the separated valid data portion is stored in the receiving buffer (RxBuf) in the 8051; the voice signal in the receiving buffer is output in the form of a PWM signal; the PWM output is driven by an 8-bit PWM engine, and the microcontroller does not need to share the processing task; finally, the voice signal is sent out via the PWM signal.

The circuit diagram of the receiving end is shown in Figure 4. The nRF24E1 chip provides a PWM output port. The PWM output signal of nRF24E1 can obtain the required audio analog signal through a first-level amplification. [page] Figure 4 Voice receiving circuit diagram At the transmitting end, the ADC performs A/D conversion on the analog audio signal sent by the microphone; the collected digital audio signal is stored in the sending buffer (TxBu f) opened in the microcontroller 8051 before it is insufficient for an RF data packet; after the sampling data is full, the 8051 stores the next data packet while transferring the full data packet to the RF front end nRF2401, and the data packet is transmitted through nRF2401. 3 System software design The function of the wireless headset is to realize two-way communication of voice. The workflow of its two parts: the plug part and the headset part is basically the same. Its workflow is as follows: 1. Power on the system and turn on the system; 2. Initialize. Initialize the timer time2, PWM output port, ADC converter, RADIO, SPI interface and wireless transceiver module nRF2401 of 8051; 3. Determine whether to send a voice signal, if yes, send it, and then go to step 4; 4. If no voice is sent, determine whether to receive a voice signal. If yes, receive it, and then go to step 3; 5. If no voice is received, repeat step 3. The corresponding flow chart is shown in Figure 5: Figure 5 Workflow chart of the plug part and the headset part. Initialization is mainly to initialize the timer time2, PWM, ADC, RADIO, SPI, and nRF2401. Among them, the timer time2 is mainly used to generate a timer interrupt trigger. In this system, time2 generates an interrupt every 125us, so that the system can digitally sample the analog audio signal output by the microphone, and its sampling frequency is 8KH z. The initialization of time2 is mainly to make time2 work normally, and overflow every 125us, thereby generating an interrupt; the nRF24E1 chip provides a PWM output port, and the output of PWM is a series of digital signals. Add a low-pass filter to the output end of PWM, and then perform a first-level amplification to obtain the required analog audio signal, and then send the obtained analog audio signal to the earphone. The PWM initialization is mainly to enable the P0.7 port to have the PWM output function, and determine that the output is 8bit, and initialize the PWMDUTY register at the same time; ADC is mainly used to perform analog-to-digital conversion on the analog voice signal sent by the microphone. The initialization of ADC is mainly to determine the 8bit quantization, and at the same time determine that the analog voice signal sent by the microphone is connected to the Channel 1 of the 9 channels; the initialization of RADIO is mainly to make nRF2401 power on and start working; the initialization of SPI is mainly to connect it with nRF2401, so as to realize the communication between the single-chip computer 8051 and nRF2401; the initialization of nRF2401 is mainly to set the operating frequency of the wireless transceiver module nRF2401, the constant frequency of the crystal oscillator, the output power of nRF2401, the address of channel 1, the data size of the data sent and received using channel 1, and the address of channel 2 and the data size of the data sent and received using channel 2. 4 Conclusion This design is a wireless headset based on the wireless voice transceiver chip nRF24E1. It is mainly used in home TVs and home computers. Of course, other additional functions can also be realized. Without the plug part, multiple headset parts can form a small wireless communication network, which can realize short-distance wireless voice communication for multiple people. Compared with other similar products, this design has the advantages of simple structure, strong anti-interference ability, good confidentiality, low power consumption and low cost. Therefore, this design has good market prospects and development prospects. References: [1]. nRF24E1 datasheet http://www.dzsc.com/datasheet/nRF24E1_1085635.html. [2]. nRF2401 datasheet http://www.dzsc.com/datasheet/nRF2401_521030.html.