Design of portable intelligent electrotherapy instrument

1 Introduction

According to statistics from the World Health Organization, "about one-third of the patients who died worldwide died from improper medication." The main reason is that due to the influence of a variety of extremely complex factors, it is difficult for the human body to grasp the right choice of medicine and dosage when it is sick. Seeking new safe and effective treatment methods has become an important topic for contemporary medical workers. This new treatment method is a method of curing diseases without conventional oral or injection drugs. Electrotherapy is a treatment method that meets this requirement. It uses different types of currents and electromagnetic fields to treat diseases. Low-frequency electrotherapy is an extremely important means in physical therapy and rehabilitation, and its efficacy has been unanimously recognized. However, most low-frequency rehabilitation treatment instruments have not yet achieved computerization, programming, and prescription, especially the comprehensive instruments with strong functions, which are still at a low level and low level, mainly manifested in: single function, cumbersome operation; aging technology, large parameter errors; poor reliability, and low safety factor. These problems of low-frequency rehabilitation treatment equipment make it difficult to be promoted and used in people's daily lives. Therefore, designing a portable intelligent electrotherapy instrument has very important practical significance.

2 Therapeutic Principles

In medicine, pulse currents with a frequency below 1000Hz are called low-frequency currents, or low-frequency pulse currents. The method of using low-frequency pulse currents to treat diseases is called low-frequency electrotherapy. Therapeutic mechanism: Low-frequency current is a kind of physical energy. When it acts on the treatment site, it causes changes in electrons and ions in the body, mainly producing physical and chemical reactions at the nerve endings, thereby causing local physiological effects. This physiological effect can activate presynaptic inhibition of the spinal cord, block ascending conduction, activate the descending pain inhibition system, and cause an increase in endogenous non-peptides and other vascular peptides, thereby playing an analgesic, anti-inflammatory, and local blood circulation promoting role; the dynamic effect of low-frequency pulse current directly stimulates nerve cells to achieve the effect of exercising and restoring function [3]. The physiological and therapeutic effects of low-frequency current include: exciting neuromuscular tissue; promoting local blood circulation; anti-inflammatory; analgesic; promoting wound healing; promoting fracture healing, etc.

Based on the theoretical knowledge of low-frequency electrotherapy, combined with some physiological conditions of women after childbirth, functional electrotherapy is adopted, and according to some technical indicators of medical device design, a portable intelligent electrotherapy device with functions such as postpartum lactation, breast duct conduction, uterine involution, postpartum urination, and postpartum recovery is designed. The electrotherapy device should be prescribed to a certain extent, allowing users to dynamically intervene in the treatment plan and treatment waveform parameters. It is simple to operate, with a maximum output intensity of 33V, safe and reliable. This machine modulates the 833Hz low-frequency pulse current into the triangular wave and trapezoidal wave required for treatment, and then combines these waveforms to obtain the required 12 treatment waveforms.

3 Technical solution To achieve the above purpose, this design adopts the following design scheme: the circuit part uses Philips' P89LPC935 microcontroller as the control core, with keyboard scanning, treatment time and treatment intensity display, D/A conversion and two-way waveform signal amplification output and other functions. The

12 different treatment waveforms of the electrotherapy device are obtained by modulating the pulse with a frequency of 833Hz. The treatment time is set by the user before treatment, ranging from 0 to 40 minutes. During the treatment, the intensity of the treatment electrical signal is adjusted by the user according to his or her own reaction, ranging from 0 to 250 levels. The electrical stimulation signal of the electrotherapy device acts on the human body through two external accessories, which are special electrodes for treatment.

4 Hardware circuit and software design of portable intelligent electrotherapy device

4.1 Hardware circuit design

The circuit part of the instrument is mainly composed of power supply circuit, CPU, digital-to-analog conversion circuit, keyboard scanning and display drive circuit, signal amplification circuit and alarm circuit. Figure 1 is the schematic diagram of the portable intelligent electrotherapy device.

Figure 1 Schematic diagram of portable intelligent electrotherapy device

In view of the design principles of portable instrument simplicity, easy operation, optimized software, and reduced size, and taking into account the characteristics, technical indicators, technical difficulty, economic cost and other factors of the system, Philips' microcontroller chip P89LPC935 was selected as the control core. P89LPC935 contains two 8-bit, 4-way step-by-step approximation analog-to-digital conversion modules and dual DA conversion channels. It can directly output analog quantities by properly configuring its function registers. The
keyboard scanning and display drive circuit uses a multifunctional peripheral chip: CH451 that integrates digital tube display drive, keyboard scanning control and μP monitoring. CH451 has monitoring functions such as power-on reset and watchdog. It is connected to the microcontroller through a high-speed 4-wire serial interface. CH451 has 18 operation commands, and the microcontroller controls CH451 through operation commands. The microcontroller reads the treatment parameters set by the user through CH451, and the treatment intensity and treatment time are displayed by 7 digital tubes through CH451.

The signal amplification circuit amplifies the waveform output by the microcontroller to the required treatment intensity, and its core component is the pulse transformer. While the waveform is increased in amplitude by the transformer, the transformer can also isolate the patient from the mains, thereby playing a role in safety protection. The amplified treatment waveform can directly act on the human body through professional treatment electrodes.

The function of the alarm circuit is that when the treatment time set by the user ends, the buzzer sounds, and the user can turn off the instrument and end the treatment.

Its working process is: after the user turns on the power, sets the treatment time, presses the function key as needed to determine the treatment project, and the microcontroller P89LPC935 as the control core scans the user's set information through the keyboard display interface chip CH451. P1.7, P0.1, P1.6 and external interrupt 0 of P89LPC935 are respectively connected to the DIN, DCLK, LOAD, and DOUT pins of CH451 as information transmission lines between the microcontroller and the keyboard display interface chip. The microcontroller calls the corresponding treatment waveform function according to the key value of the scanned function key. The function of the treatment waveform function is to modulate the pulse with a frequency of 833Hz into a triangular wave or a trapezoidal wave whose amplitude and period change with the intensity set by the user. The waveform is output through the DAC0 port of the microcontroller. The treatment waveform acts on the human body through the dedicated treatment electrode after passing through the subsequent amplification circuit. When the start button is pressed, the displayed treatment time decreases second by second. When the treatment time set by the user ends, the P0.0 of the microcontroller outputs a high level, and the alarm circuit sends an alarm signal to notify the user that the treatment has ended, and the user can turn off the power.

4.2 Software Design

Waveform modulation principle:

Modulated waveform

Modulation waveform

Figure 2 Waveform modulation principle

Parameter description:

During the treatment process, the voltage output is jumping, 130mV is a level, so every time a new step appears, the voltage will jump to multiples of 130mV.

scope is the amplitude variable, this value is equal to the intensity of the treatment device during treatment (unit: mV);
up is the number of fundamental waves of the same amplitude contained in each step in the rising stage; high is the number of fundamental waves when the amplitude reaches the maximum value and remains unchanged;
down is the number of 130mv voltage levels between adjacent step voltages in the falling stage (unit: pieces); low is the length of the amplitude of 0 (unit: ms).
By setting these 4 parameters, 16 basic waveforms can be obtained. By combining these 16 basic waveforms in a certain order, 12 therapeutic waveforms with specific functions can be obtained. The main program flow is shown in Figure 3.

Figure 3 Main program flow

5 Main technical indicators of portable intelligent electrotherapy device

(1) Pulse frequency 833Hz, tolerance ±10%.
Pulse width 0.4ms, tolerance ±10%.
The output amplitude is adjusted continuously and evenly, each increment is 130mV, and the change rate is less than 3%.
Single pulse power The maximum output amplitude is greater than 7μC.
Single pulse energy The maximum output energy does not exceed 300mJ
(2) Treatment waveform width: Determined by the input treatment intensity: the greater the intensity, the greater the pulse group width; the smaller the intensity, the smaller the pulse group width.
(3) Amplitude modulation: using trapezoidal wave and triangle wave, the rise time and fall time are also related to the input intensity.
(4) 12 function keys, you can select the corresponding treatment prescription according to the treatment project. 12 treatment plans: fundamental wave 1, fundamental wave 2, fundamental wave 3, fundamental wave 4, treatment project I, treatment project II, postpartum lactation, low milk secretion, milk duct obstruction, uterine involution, postpartum urination promotion, postpartum recovery.
(5) Amplitude range: The amplitude range of the original waveform is 0-2.56V, and the amplitude range after amplification by the amplifier circuit is 0-33V.
(6) Treatment time: 0-40min; Treatment intensity: 0-250 levels.

6 Conclusion

The author's innovation: The electrotherapy device overcomes the defects of traditional electrotherapy equipment and realizes intelligence to a certain extent. It adopts single-chip microcomputer control, has strong reliability and high safety factor, and the treatment function is prescription-based and has strong functionality. The therapeutic device has low power consumption, small size, light weight, and wide application. It is not only suitable for medical institutions at all levels, but also can be widely used in families for treatment and health care.