Development of brain wave therapeutic instrument based on single chip microcomputer

　　The rapid development of society and science and technology has brought us a high-quality life, but in the complex and tense social changes, people are also under increasing pressure, and many physical and mental problems such as insomnia, depression, mania, and emotional instability are becoming increasingly serious. Therefore, it is of great practical significance to develop an effective psychotherapy instrument. Studies have found that at certain frequencies, especially in the α and θ range, stimulating the human brain with rhythmic flashes can reduce the anxiety symptoms of the test subjects; at the same time, scientists have investigated the auditory drive of brain waves, that is, using sounds of special frequencies (such as rhythmic ticking, tones or vortex sound vibrations) to stimulate the brain, and then using EEG (electroencephalogram) equipment to monitor the brain. The results show that the brain does respond to rhythmic auditory stimulation at the same frequency as the sound by increasing brain activity. Studies have found that under the dual induction of sound and light, the two hemispheres of the brain enter a more combined or synchronized state (brain sync), that is, the brain wave synchronization state, and induce the human brain to produce brain waves of α, β, θ, and δ frequencies, which are crucially related to the mental state of the person. The relationship between brain waves and human mental state is shown in Table 1.

　　According to this principle, the dual guiding effects of sound and light can be used to induce the human brain to produce rhythmic waves of four frequencies: α, β, θ, and δ, thereby enabling a person's emotions to be quickly and effectively released, as well as positively improved.

　　l System design and implementation

　　As shown in Figure 1, the system periphery includes: digital-to-analog converter, multi-channel analog switch, electrodes, photoelectric glasses, stereo headphones, buttons, LED display, indicator light display, etc.

　　Brainwave therapy system structure diagram

　　This design uses AT89C52 as the core chip. The single-chip microcomputer P0 port outputs digital signals. After passing through the digital-to-analog conversion circuit composed of DAC0832, we get the sinusoidal amplitude modulated wave signal required for treatment. After the signal passes through the analog switch CD4053, two signals with a certain time difference are generated. After the two signals are processed by the preamplifier circuit composed of LM324 and the audio power amplifier circuit composed of TDA2030, the output signal can enable the listener to hear these special frequency therapeutic waves through stereo headphones. Furthermore, external music (such as CD, MP3, etc.) can be input from the front of the audio power amplifier. While playing some natural music during treatment, it can better relieve tension and achieve good treatment effects. In addition, the two signals pass through the detection circuit composed of LM324, and then the LM3915 drives the strip LED light-emitting tube to emit light, and the display number of the strip LED light-emitting tube is used to intuitively display the intensity of the sound signal.

　　In addition, the signal output by the P0 port of the microcontroller also passes through the digital-to-analog conversion core circuit to obtain a series of pulse signals with a preset frequency. The pulse intensity can also be displayed by the LED strip light-emitting tube.

　　The preset optical frequency signal generated by the microcontroller ports RXD and TXD is output from the photoelectric glasses through the optical signal driving circuit, and its output status is displayed by the LED indicator.

　　2 System Hardware Implementation

　　2.1 Detection Circuit Design

　　LM324 is a four-op-amp integrated circuit that uses a 14-pin dual in-line plastic package. There are four operational amplifiers inside, with a phase compensation circuit, low power consumption, and a wide operating voltage range. It can work with a positive power supply of 3~30V, or a positive and negative dual power supply of ±1.5V~±15V. This circuit is used to measure the intensity value of signals in different frequency bands, and as a bandpass filter, it can select signals in different frequency bands. The number of light-emitting diodes on the display indicates the size of the signal amplitude. The circuit design is shown in Figure 2. Since the therapeutic wave is a high-frequency sinusoidal amplitude modulated wave, we can detect the envelope of the therapeutic wave using the bandpass filter circuit composed of LM324.

　　2.2 Sound and light intensity display circuit design

　　LM3914 is a monolithic integrated circuit used to detect analog signal level and drive 10-bit LED for linear analog display. It can easily realize voltage indication, scale expansion, zero indication, visual alarm, timing generation and other purposes. The processed sound and light signal is input from pin 5. The number of LEDs displayed corresponds to the input voltage, so that the intensity of sound and light is intuitively displayed by the number of LEDs lit. The connection of the display circuit is shown in Figure 3.[page]

2.3 Optical signal driving circuit design

　　The optical signal of the system is output by the serial port RXD and TXD of the single chip microcomputer. The optical signal consists of a series of narrow pulses with special duty cycle and adjustable frequency. Through this driving circuit, the load capacity of the system can be improved to meet the requirements of multi-channel output. This circuit constitutes a two-stage emitter follower circuit, Au=1. By adjusting the resistor R2, the intensity of the output signal can be adjusted.

　　2.4 Power Circuit Design

　　This treatment system mainly needs to provide ±12V DC voltage for the op amp circuit, +5V voltage for the single-chip control circuit, and a 5V reference voltage for the digital-to-analog conversion chip. Therefore, the entire system requires ±5V and ±12V DC voltages. The power supply circuit is designed as follows. The mains power passes through the integrated voltage module to obtain the required DC voltage to power the sound, light and pulse control circuits. As shown in Figure 5:

　　3 System Software Design

　　The system software requires to be edited in C51 language or assembly language. The system software functions mainly include: sound and light control and electrotherapy pulse control process. The process of the sound and light control part includes initializing the microcontroller first, then selecting the program, and then executing the preset functions, including volume increase and decrease function, audio increase and decrease function, monitoring function, noise/audio function, and run/hold function. The flow chart of the sound and light control part of the system is shown in Figure 6. The flow chart of the electrotherapy pulse part includes: initializing the microcontroller and setting the pulse function.

　　4 Results and discussion

　　Experiments have shown that this therapeutic device can obtain therapeutic signals of different frequencies. Clinical tests are still needed to determine the effectiveness of the treatment, and continuous improvements will be made based on feedback. The existing functions of the therapeutic device can basically meet most practical work needs. At the same time, the application of the device will be more flexible by upgrading the software and adding user-defined stimulation schemes to the electrical stimulation control and light stimulation parts.

References:

[1]. AT89C52 datasheet http://www.dzsc.com/datasheet/AT89C52_1064535.html.
[2]. LM324 datasheet http://www.dzsc.com/datasheet/LM324_1054816.html.
[3]. TDA2030 datasheet http://www.dzsc.com/datasheet/TDA2030_1059048.html.
[4]. LM3915 datasheet http://www.dzsc.com/datasheet/LM3915_1060974.html.
[5]. LM3914 datasheet http://www. dzsc.com/datasheet/LM3914_1060973.html.