Rechargeable battery and stand-alone fast charger design

At present, electronic therapeutic devices that use two electrodes to symmetrically cover the treatment part of the human body are used. The pulsating voltage on the electrode acts on the resistance of the treatment part of the human body to generate a pulsating current that the human body can perceive at the treatment part, stimulate the nerves and muscles, make them contract and relax, and produce a motion effect to achieve the purpose of treatment. However, there are only a few types of pulsating voltages generated by this type of therapeutic device on the market. Since the frequency cycle of the pulsating current is fixed, if a certain treatment part is subjected to its pulsation for a long time, it will produce an anti-treatment effect, causing spontaneous tension, thereby reducing the treatment effect. In order to solve this problem, the random music signal emitted by the MP3 is introduced into the therapeutic device, so that the audio signal is modulated with the 2.4 kHz intermediate frequency treatment frequency to generate a variety of pulsating voltages and pulsating currents with constantly changing frequency cycles. They act as the music signal fluctuates, allowing patients to receive treatment while enjoying their favorite music, distracting their attention and relieving tension, thereby helping to improve the treatment effect.

A design of an electronic therapeutic instrument based on the embedded device AT89C5ISNDlC is proposed, and external D/A, mass storage, keyboard and display are expanded to realize basic MP3 functions; AT89C5lSNDlC is controlled to generate audio and 2.4 kHz intermediate frequency signals, and digital circuits are used to complete the frequency modulation of these two signals. After amplification, the pulsating therapeutic voltage is output by transformer isolation.

1 Working Principle

The hardware structure of the electronic therapeutic instrument system based on the embedded device 89C51SND1C is shown in Figure 1, which is divided into three parts: signal generation and control module, frequency modulation output module, and power supply module.

The signal generation and control module is composed of 89C51SND1C single-chip microcomputer, mass storage, keyboard, USB port, LCD display, D/A converter, audio amplifier and other parts. When the USB port of the therapeutic instrument is inserted into the USB interface of the computer, the USB disk function is executed after detection by the single-chip microcomputer, and the selected MP3 songs can be copied to the USB disk (therapeutic instrument). When the USB port of the therapeutic instrument is not inserted into the USB interface of the computer, the therapeutic instrument can be used as an MP3 broadcaster. The song, treatment time and volume are set through the function keys, and the therapeutic instrument is controlled through the start/stop key. During treatment, the single-chip microcomputer generates two inverted 2.4 kHz intermediate frequency signals FIF, FIF and an audio signal Faudio, and decodes the stored MP3 format songs into audio digital signals, which are then amplified by the D/A conversion amplifier and sent to headphones or speakers.

The FM output module is composed of FM, amplification, output dose adjustment, output transformer, electrode sheet and other parts. The two inverted intermediate frequency signals and one audio signal are FM-modulated. After the FM-modulated signals are amplified, the output pulse voltage is isolated by the output transformer and symmetrically covered to the treatment part of the human body through the electrode sheet. The human body will feel the current stimulation that changes with the music. Through the output dose adjustment, the requirements of the perceptible current that can be tolerated by different treatment parts of the human body and the different dryness and humidity of the skin can be met.

The power module can provide 15 V, 5 V, and 3.3 V system operating voltages. When the USB port of the therapeutic device is plugged into the USB port of the computer, the microcontroller executes the U disk function, and the computer USB port provides +5 V power. During treatment, the power supply of the therapeutic device is generated by 220 V AC power through transformation, rectification, voltage stabilization, and filtering.

2 Hardware System Design

2.1 MCU Introduction

The embedded device AT89C51SND1C integrates CPU, MP3 decoder, USB controller and other devices. AT89C51SND1C not only has the control function of 51 series microcontroller, but also can be expanded to MP3 and USB disk. It adopts PLCC package. Its internal structure block diagram is shown in Figure 2.

The P0, P1, and P3 ports of AT89C51SND1C are compatible with the 51 series microcontrollers, and an 8-bit P4 port and a 4-bit P5 port are added. The connection method of the clock circuit and reset circuit is the same as that of the 51 series microcontrollers.

When using the device for the first time, you need to download the USB driver and user program separately. In the 64 KBROM of AT89C51SNDlC, the address FOOOH-FFFFH has been assimilated with 4K bytes of Boot Loader code. When leaving the factory, the BLJB position has been set to 1, so that the Boot Loader code is automatically executed after power-on, waiting to download the USB flash drive driver or user program target code from the USB interface. After the download is completed, the BIJJB position should be set to 0 in the download software, and the user program will be automatically executed after power-on again. If the user program still needs to be modified, the ISP pin can be set to a low level. Then, after power-on reset, it will automatically boot and execute the Boot Loader code, waiting to update the user program. To restart the user program, the ISP pin should be set to a high level.

2.2 Signal generation and control module

The circuit diagram of the signal generation and control module is shown in Figure 3. To realize the MP3 and U disk functions, the AT89C51SNDlC microcontroller needs to be connected to an external NAND-Flash mass storage. Here, the 16 MB K9F2808U0C is selected, and its data lines I/00~I/07 are connected to the P0 port, and the control line is connected to the P5 port. The MP3 audio decoding output signal, and the DOUT, DLCK, DSEL, and SCLK pins of the microcontroller are connected to the D/A converter CS4330, which is amplified and output to the headphones to listen to the songs played by the MP3. The LCD screen is connected to the P2 port of the microcontroller and cooperates with the keyboard to display the current working status of the therapeutic device. There are 4 buttons on the keyboard. The volume/song/timing function key is connected to the P1.0 pin, which cooperates with the next key connected to the P1.1 pin and the previ-OHS key connected to the P1.2 pin to realize the volume adjustment, song selection, treatment timing and other function settings; and the start/stop key is connected to the P1.3 pin.

The P3.3 pin of the AT89C5lSNDlC microcontroller is used to detect whether the USB flash drive or MP3 player is currently in use. If the USB lead of the therapeutic device is connected to the USB port of the computer, the P3.3 pin detects a high level and executes the USB flash drive program. At this time, the working power of the microcontroller comes from the USB interface; otherwise, the P3.3 pin detects a low level and executes the MP3 program. The intermediate frequency signals FIF, FIF and the audio signal Faudio are connected to the P4.4, P4.5 and DOUT pins of the AT89C5lSN-DlC microcontroller respectively.

2.3 FM output module

The circuit schematic diagram of the FM output module is shown in Figure 4. The audio signal Faudio is modulated with the intermediate frequency signal FIF and IF phase respectively to generate two modulation waveforms with opposite phases, which are then amplified by 9013, 8050, and D880Y and sent to the two input ends of the transformer. The voltage of the transformer middle tap can be adjusted by the dose adjustment circuit connected to the milliammeter. The 47 kΩ potentiometer is the dose adjustment potentiometer. If it is adjusted downward, the current indicated by the milliammeter becomes smaller, and vice versa. The transformer isolates the output voltage change synchronously with the input voltage. The output voltage contacts the human body through the electrode sheet and generates a sensed current in the human body. The sensed current of the human body is different depending on the different parts of the physical therapy and the dryness and wetness of the skin. During physical therapy, the potentiometer needs to be adjusted to make the physical therapist feel comfortable.

2.4 Power Module

The 3.3 V, 5 V, and 15 V working voltages required by the therapeutic device all come from the power module, and its principle is shown in Figure 5. The 3.3 V voltage can be provided to the embedded device AT89C51SNDlC; the 5 V voltage can be provided to the frequency modulation and amplification circuits; and the 15 V voltage can be provided to the output dose adjustment circuit. Among them, the 5 V voltage regulator uses 78L05, and the 3.3 V voltage regulator uses LDll17S33. When using the U disk function, the USB port of the therapeutic device is inserted into the USB port of the computer, and the 220 V AC power supply is not connected. The working voltage of the microcontroller is provided by the USB port.

3 System Software Design

In coordination with the hardware circuit function, the system software design process is shown in Figure 6; the keyboard interrupt service program process is shown in Figure 7.

4 Conclusion

The designed portable device battery monitoring system uses the programmable battery power monitoring chip BQ27210 and the external highly integrated processor C805lF304 to realize real-time monitoring of battery power, usable time, temperature, voltage and other information, and transmits and processes data through the I2C bus. It has the characteristics of high precision, small size and low cost, and has been applied to some handheld data acquisition devices.