Circuit for detecting concentration of electrolyte in body fluid and signal processing device

Abstract

The invention discloses a detection circuit for electrolyte concentration in body fluid and a signal processing device, and belongs to the technical field of electrical electronics and sensors. Comprising a front-end analog circuit, a Bluetooth module, a microcontroller circuit, a power management circuit, an intelligent terminal monitoring APP, a battery and a leading-in end, the front-end analog circuit, the Bluetooth module, the microcontroller circuit and the power management circuit are sequentially connected, and the power management circuit is further connected with the front-end analog circuit and a conversion circuit. According to the device, the concentration detection of various trace ions in wearable sweat is realized, the device is wider in detection range, the detection range is 0-500mV, the detection precision is higher, the detection error is 1mV after the device is compared with a commercial electrochemical workstation, various potential signals are detected according to the change of a front-end electrochemical sensor, and the detection accuracy is higher. The method can be widely applied to detection of human body weak potential signals.

Description

Technical Field

[0001] The present invention relates to the field of electrical engineering, electronics and sensor technology, and in particular to a circuit for detecting electrolyte concentration in body fluid and a signal processing device. Background Art

[0002] The Internet of Things has changed traditional medical diagnosis with the concept of telemedicine and e-health care, and the monitoring technology of physical indicators such as electrocardiogram, electromyography and electroencephalogram has become increasingly mature. In recent years, the sensing technology for human epidermal fluids has developed rapidly. In particular, the detection of electrolyte (sodium ion, potassium ion, calcium ion, etc.) concentration in human body fluids (sweat and interstitial fluid, etc.) can realize the daily monitoring of chronic diseases such as kidney disease, and can also be used for physiological indication monitoring of special personnel such as athletes and firefighters. Wearable sensors that realize the detection of electrolytes in human epidermal fluids can accurately collect and analyze biochemical indicators, making the information of individuals, doctors and hospitals seamlessly connected, which is of great significance for the formation of a personal-centered precision health care model.

[0003] The key to achieving the detection of human sweat markers is to wirelessly transmit the physiological signals collected by wearable sensors to smart terminals or cloud models after processing and analysis, so as to provide real-time feedback on physiological status and model iteration. Wearable potentiometers have electronic circuits that control and measure current and voltage, which are necessary for electrical analysis and wireless signal transmission. Currently, there are related explorations of portable or wearable detection circuits and signal processing that can perform most electrochemical techniques, but the price is about several thousand dollars, and the cost issue hinders their widespread application. The components and circuit design of commercial potentiostats are proprietary, which is difficult for those who need to develop affordable potentiostats for research.

[0004] Existing research has explored the electrolyte concentration detection circuit and signal processing device in body fluids. National invention patent 202311581910.9 discloses a wearable sweat sensor assembled with modular circuits, microcontroller circuits, electrochemical modules and sweat-inducing modules, to extract sweat and detect components in a resting state. The microcontroller circuit includes a Bluetooth chip and a microcontroller chip connected to each other, and the microcontroller chip is connected to the connection circuit. The device cannot take into account the electrolyte detection of multiple body fluids. National invention patent 202210502090.9 discloses a multi-parameter wearable sweat collection circuit and device based on electrochemistry, which realizes real-time collection and processing of sweat multi-parameter ion data, effectively converts, merges and transmits the data, and improves the accuracy and stability of the output signal, but the device still cannot take into account the electrolyte detection of multiple body fluids. Dstat developed by foreign scholars Dryden et al. and the constant potentiostat / galvanostat for characterizing thin-film batteries developed by Dobbelaere et al. are used for electrochemical current detection. Usually these open source potentiometers are designed to be used with a computer via a wired connection to a USB port, and remote signal transmission and communication are not possible.

[0005] The difficulties in developing an electrolyte concentration detection circuit and signal processing device in body fluids lie in the following aspects. First, the electrolyte concentration content in epidermal body fluids such as human sweat and interstitial fluid varies over a large range and has a low concentration, requiring the detection circuit to have a large test range and high detection accuracy. Since the electrolyte concentration in human body fluids is affected by external factors such as body temperature, the collected signal noise is large, requiring the design of corresponding signal processing and circuits and special modules. Finally, the electrolyte concentration signal collected by the wearable sensor must be processed and analyzed and then wirelessly transmitted to the smart terminal or cloud model for further application and analysis. Remote data transmission is also a problem. Summary of the invention

[0006] The purpose of the present invention is to provide a circuit for detecting electrolyte concentration in body fluids and a signal processing device, which has a wider detection range, a detection range of 0-500mV, and a higher detection accuracy. According to the change of the front-end electrochemical sensor, a variety of potential signals can be detected, which can be widely used in the detection of weak potential signals of the human body.

[0007] To achieve the above-mentioned purpose, the present invention provides a circuit for detecting electrolyte concentration in body fluids and a signal processing device, comprising a front-end analog circuit, a Bluetooth module, a microcontroller circuit, a power management circuit, a battery and an introduction end. The front-end analog circuit, the Bluetooth module, the microcontroller circuit and the power management circuit are connected in sequence, and the power management circuit is also connected to the front-end analog circuit and the microcontroller circuit respectively. The introduction end includes two electrode connectors, which are respectively connected to WE and RE in an open circuit potential acquisition circuit. The front-end analog circuit includes an instrument amplifier module and a filter module, which are AD8606 and AD8608 respectively.

[0008] Preferably, the lead-in terminal WE in the instrument amplifier module is connected to the positive electrode of the operational amplifier A1, a resistor R1 is connected in series between the negative electrode of the operational amplifier A1 and its output terminal, and a resistor R3 is connected in series between the output terminal of the first operational amplifier and the negative electrode of the operational amplifier A3; similarly, the lead-in terminal RE is connected to the positive electrode of the operational amplifier A2, a resistor R2 is connected in series between the negative electrode of the operational amplifier A2 and its output terminal, and a resistor R4 is connected in series between the output terminal of the operational amplifier A2 and the positive electrode of the operational amplifier A3; at the same time, a resistor Rg is connected in series between the negative electrode of A1 and the negative electrode of A2, and this resistor is a gain resistor; a resistor R6 is connected in series between the positive electrode of A3 and the ground, and forms a subtraction amplifier circuit with R3, R4, and R5.

[0009] Preferably, the relationship between the input and output potentials in the instrument amplifier module is shown by the formula, wherein R1=R2, R3=R4, R5=R6, and R1=Rg, R5=R3 are artificially set.

[0010] Preferably, the filter module includes resistors R7 and R8 connected in series with the positive electrode of the operational amplifier A4, the output end of the operational amplifier A4 is connected to the negative electrode, the resistor R8 is connected in parallel with the output end of the operational amplifier A4 and two capacitors C1 and C2, the resistors R9 and R10 are connected in series with the operational amplifier A5, the output end of the operational amplifier A5 is connected to the negative electrode, the resistor R10 is connected in parallel with the output end of the operational amplifier A5 and two capacitors C3 and C4, and the resistor C3 is connected in series between the operational amplifier A4 and the ground.

[0011] Preferably, the microcontroller circuit includes STM32F103RET6, wherein the PD0 and PD1 pins of the MCU are externally connected to an 8MHz crystal oscillator to provide a reference frequency to the STM32 as a clock reference; the PA2 pin of the STM32 F103RET6 in the MCU module is connected to pin 1 of the operational amplifier chip AD8606 in the front-end circuit.

[0012] Preferably, the ADC sampling pre-division in the microcontroller circuit is set to 6, the ADC clock frequency is 12 MHz, and the ADC sampling time is 55.5 clock cycles.

[0013] Preferably, the MCU is also used to run the protocol stack program required for Bluetooth communication. After the MCU collects the voltage signal, it is transmitted to the Bluetooth module via USART and the data is broadcast.

[0014] Preferably, the Bluetooth module includes a receiving end RXD and a transmitting end TXD pin, PA9 is connected to the receiving end RXD pin of the Bluetooth module as a transmitting end, wherein PA10 is connected to the transmitting end TXD pin of the Bluetooth module as a receiving end.

[0015] Preferably, the power management circuit includes a boost converter and a buck converter. The boost converter is TPS613222ADBVR, which is used to convert the 3.3V standard voltage into a 5V voltage for providing operating voltage for AD8606 and AD8608 op amp chips; the buck converter is TPS76333DBVR, which is used to convert the 3.7V output voltage of the lithium battery into 3.3V for powering STM32 and the Bluetooth module.

[0016] Therefore, the present invention adopts a body fluid electrolyte concentration detection circuit and a signal processing device of the above structure, which has the following beneficial effects: The present invention has a wider detection range of 0-500mV, a higher detection accuracy, and can detect a variety of potential signals according to the change of the front-end electrochemical sensor, and can be widely used in the detection of weak potential signals of the human body. The present invention also has a Bluetooth module, which can realize wireless transmission of signals.

[0017] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of a circuit for detecting electrolyte concentration in body fluid and a signal processing device of the present invention; Figure 2 It is a schematic circuit diagram of an instrument amplifier module of a body fluid electrolyte concentration detection circuit and a signal processing device of the present invention; Figure 3 It is a circuit diagram of a filter module of a circuit for detecting electrolyte concentration in body fluid and a signal processing device of the present invention; Figure 4 A schematic diagram of a microcontroller circuit of a body fluid electrolyte concentration detection circuit and a signal processing device of the present invention; Figure 5 A schematic diagram of a Bluetooth module of a circuit for detecting electrolyte concentration in body fluids and a signal processing device according to the present invention; Figure 6 The present invention is a schematic diagram of a power management circuit of a body fluid electrolyte concentration detection circuit and a signal processing device. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0020] Unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0021] Example The present invention provides a circuit for detecting electrolyte concentration in body fluid and a signal processing device, such as Figure 1 As shown. It includes: front-end analog circuit, Bluetooth module, microcontroller module and power management module; wherein the front-end analog circuit, microcontroller module, Bluetooth module, smart terminal monitoring APP and power management module are connected in sequence, and the power management module is also connected to the front-end analog circuit and microcontroller module respectively. The front-end analog circuit is used to collect voltage signals of different ions in sweat through electrochemical sensors and transmit the collected voltage signals to the microcontroller module; Bluetooth module, used for transmitting detection signals between the detection system and the smart terminal monitoring APP; Microcontroller module, used for converting analog signals into digital signals and processing the signals; Smart terminal monitoring APP, used to visualize the detection signals transmitted by the detection system; A power management module, used to supply power to the above-mentioned circuits; Preferably, the front-end analog circuit mainly uses an open circuit potential-time curve method to collect voltage signals generated by ions in sweat, and transmits the collected voltage signals to a microcontroller module; The front-end analog circuit includes an instrumentation amplifier module and a filter module, which mainly includes two operational amplifier chips, AD8606 and AD8608, and a series of resistors with different resistance values; First, due to the movement of ions, the electrochemical sensor generates a potential difference due to the different potentials of the two electrodes. The front-end acquisition module has two interfaces, WE and RE, to collect the potentials of different electrodes. The acquisition module consists of two parts. First, the potential value passes through the instrument amplifier circuit. The instrument amplifier consists of two in-phase amplifiers and a differential amplifier. Compared with ordinary operational amplifiers, it has the following characteristics: high common-mode rejection ratio, high input impedance, extremely low output impedance, low noise, precise gain setting and differential input structure.

[0022] The topology circuit diagram of the instrument amplifier is as follows: Figure 2 As shown, in the open circuit potential acquisition circuit, WE is an ISE (ion selective electrode) and RE (reference electrode) to form a two-electrode system, wherein the acquisition terminal WE is connected to the positive electrode of the operational amplifier A1, a resistor R1 is connected in series between the negative electrode of the operational amplifier A1 and its output terminal, and a resistor R3 is connected in series between the output terminal of the first operational amplifier and the negative electrode of the operational amplifier A3; similarly, the acquisition terminal RE is connected to the positive electrode of the operational amplifier A2, a resistor R2 is connected in series between the negative electrode of the operational amplifier A2 and its output terminal, and a resistor R4 is connected in series between the output terminal of the operational amplifier A2 and the positive electrode of the operational amplifier A3; at the same time, a resistor Rg is connected in series between the negative electrode of A1 and the negative electrode of A2, and this resistor is a gain resistor; a resistor R6 is connected in series between the positive electrode of A3 and the ground, and forms a subtraction amplifier circuit with R3, R4, and R5. Among them, operational amplifiers A1 and A2 are in-phase differential input mode. The in-phase input can greatly increase the input impedance of the circuit and reduce the circuit's attenuation of weak input signals; the differential input can make the circuit only amplify the differential mode signal and only follow the common mode input signal, so that the amplitude ratio of the differential mode signal sent to the subsequent stage to the common mode signal (i.e., the common mode rejection ratio CMRR) is improved.

[0023] Better, the relationship between the input and output potentials is shown by the formula, where R1=R2, R3=R4, R5=R6, and R1=Rg, R5=R3 are artificially set.

[0024] Since the voltage noise generated by the electrochemical sensor is in the high frequency band, a low-pass filter is selected. The topology of the filter circuit is as follows: Figure 3 As shown, after the output voltage VOUT1 of the front instrument amplifier is connected, the filter module circuit is connected. The circuit is a SK fourth-order low-pass filter composed of two operational amplifiers and a series of resistors and capacitors with different resistance values. Resistors R7 and R8 are connected in series with the positive electrode of the operational amplifier A4, and the output end of the operational amplifier A4 is connected to the negative electrode. Resistor R8 is connected in parallel with two capacitors at the output end of the operational amplifier A4. At the same time, a resistor C3 is connected in series between the operational amplifier A4 and the ground, forming a 2nd-order SK low-pass filter as a whole. The entire filter circuit is composed of two 2nd-order SK low-pass filters in series.

[0025] like Figure 4As shown in the figure, the microcontroller module is mainly responsible for data acquisition, processing, transmission and power supply to the Bluetooth module. The module is mainly based on STM32F103RET6. The chip has three 12-bit ADCs and one DAC module, so there is no need for an external A / D conversion circuit. In addition, the PD0 and PD1 pins of the MCU are connected to an 8MHz crystal oscillator to provide a reference frequency to the STM32 as a clock reference to ensure the stability of the microcontroller operating frequency; in addition, a reset switch and five filter capacitors are also connected. After the front-end acquisition module performs differential and filtering processing on the voltage of the electrochemical sensor, the pin 1 of the op amp chip AD8606 is connected to the PA2 pin of the STM32F103RET6 in the MCU module, which is the definition pin of the No. 1 ADC.

[0026] In this embodiment, the relationship between the collected electrical signal and the concentration of the ion to be measured conforms to the Nernst equation, and the concentration of each ion in sweat can be accurately detected at the same time. During signal acquisition, the microcontroller module MCU obtains the data collected by the ADC through DMA. Since the peripherals can directly exchange data with the memory, the step of transferring through the CPU is omitted, so the data transmission speed is faster and more efficient. After using DMA, the CPU no longer needs to process a large number of I / O operations, so it can focus on performing other tasks, improving the overall performance of the system. The detection system has high requirements for real-time performance, so the use of DMA is more suitable for the application scenario.

[0027] More preferably, the main frequency of the signal generated by the electrochemical sensor is below 50kHz. According to the Nyquist theorem, in order to ensure signal quality, the ADC sampling frequency should be at least twice the highest frequency of the signal. In the ADC sampling setting, the pre-scaling is set to 6, so the ADC clock frequency is 12MHz, and the ADC sampling time is 55.5 clock cycles. According to the formula TCONV (conversion time) = sampling time (set sampling cycle) + 12.5 cycles, and sampling frequency = clock frequency / conversion time, the ADC sampling frequency is calculated to be 176kHz, which meets the Nyquist theorem.

[0028] The MCU is also used to run the protocol stack program required for Bluetooth communication. After the MCU collects the voltage signal, it is transmitted to the Bluetooth module through USART and the data is broadcast.

[0029] like Figure 5As shown, in order to reduce the power consumption of the overall circuit and reduce the size of the circuit, the Bluetooth transmission circuit uses the CH9140 Bluetooth serial port module. The Bluetooth module is a low-power Bluetooth module that supports BLE4.2. The asynchronous serial port baud rate is 115200bps. It is compatible with existing serial port software and tools, and does not require secondary development. The module is mainly used for data transmission between the detection system and the mobile terminal system, and transmits the data to the host computer in real time, which is convenient for users to detect the detection object in real time. The chip is mainly used as a slave to send and receive data. When the ion concentration is detected, the working mode of the Bluetooth module is notification, where the UUID of the communication is 0xFFF1, and the serial port receives data and sends it to the host through this channel. The host needs to turn on the notification, and the data will be packaged in MTU size. The excess will be sent by the chip in packets. Among them, the PA9 pin of the MCU is used as the data sending pin, and PA10 is used as the data receiving pin. PA9 is connected to the receiving end RXD pin of the Bluetooth module as the sending end, and PA10 is connected to the sending end TXD pin of the Bluetooth module as the receiving end.

[0030] like Figure 6 As shown in the figure, the power management module includes a boost converter and a buck converter. The external lithium battery has a specification of 3.7V and 650mAh, which can support the device to run continuously for more than 20 hours during the data collection process. The buck converter uses the chip TPS76333DBVR from TI (Texas Instruments), which can convert the 3.7V output voltage of the lithium battery into 3.3V for powering the STM32 and Bluetooth module. The boost converter uses the chip TPS613222ADBVR from TI (Texas Instruments), which can convert the 3.3V standard voltage into 5V voltage to provide operating voltage for the AD8606 and AD8608 op amp chips.

[0031] Therefore, the present invention adopts the above-mentioned electrolyte concentration detection circuit and signal processing device in body fluids to realize the concentration detection of various trace ions in wearable sweat. The detection range of the device is wider, and its detection range is 0-500mV, and the detection accuracy is higher. After comparison with a commercial electrochemical workstation, its detection error is 1mV. According to the change of the front-end electrochemical sensor, a variety of potential signals can be detected, which can be widely used in the detection of weak potential signals of the human body.

[0032] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A circuit for detecting electrolyte concentration in body fluid and a signal processing device, characterized in that: It includes a front-end analog circuit, a Bluetooth module, a microcontroller circuit, a power management circuit, an intelligent terminal monitoring APP, a battery and an introduction end. The front-end analog circuit, the Bluetooth module, the microcontroller circuit and the power management circuit are connected in sequence. The power management circuit is also connected to the front-end analog circuit and the conversion circuit respectively. The introduction end includes two electrode connectors, which are respectively connected to WE and RE in the open circuit potential acquisition circuit. The front-end analog circuit includes an instrument amplifier module and a filter module, which are AD8606 and AD8608 respectively. A front-end analog circuit is used to collect voltage signals of different ions in sweat through an electrochemical sensor and transmit the collected voltage signals to a microcontroller circuit; Bluetooth module, used for the transmission of detection signals between the detection system and the smart terminal monitoring APP; Microcontroller circuit, used for converting between analog signals and digital signals and processing the signals; Smart terminal monitoring APP, used to visualize the detection signals transmitted by the detection system; The power management circuit is used to supply power to the above-mentioned circuits.

2. The circuit for detecting electrolyte concentration in body fluid and the signal processing device according to claim 1, characterized in that: The lead-in terminal WE in the instrument amplifier module is connected to the positive electrode of the operational amplifier A1, a resistor R1 is connected in series between the negative electrode of the operational amplifier A1 and its output terminal, and a resistor R3 is connected in series between the output terminal of the first operational amplifier and the negative electrode of the operational amplifier A3; similarly, the lead-in terminal RE is connected to the positive electrode of the operational amplifier A2, a resistor R2 is connected in series between the negative electrode of the operational amplifier A2 and its output terminal, and a resistor R4 is connected in series between the output terminal of the operational amplifier A2 and the positive electrode of the operational amplifier A3; at the same time, a resistor Rg is connected in series between the negative electrode of A1 and the negative electrode of A2, and this resistor is a gain resistor; a resistor R6 is connected in series between the positive electrode of A3 and the ground, and forms a subtraction amplifier circuit with R3, R4, and R5.

3. The circuit for detecting electrolyte concentration in body fluid and the signal processing device according to claim 2, characterized in that: The relationship between the input and output potentials in the instrument amplifier module is shown by the formula, where R1=R2, R3=R4, R5=R6, and R1=Rg, R5=R3 are artificially set.

4. The circuit for detecting electrolyte concentration in body fluid and the signal processing device according to claim 1, characterized in that: The filter module includes resistors R7 and R8 connected in series with the positive electrode of the operational amplifier A4, the output end of the operational amplifier A4 is connected to the negative electrode, the resistor R8 is connected in parallel with the output end of the operational amplifier A4 and two capacitors C1 and C2, the resistors R9 and R10 are connected in series with the operational amplifier A5, the output end of the operational amplifier A5 is connected to the negative electrode, the resistor R10 is connected in parallel with the output end of the operational amplifier A5 and two capacitors C3 and C4, and the resistor C3 is connected in series between the operational amplifier A4 and the ground.

5. The circuit for detecting electrolyte concentration in body fluid and the signal processing device according to claim 1, characterized in that: The microcontroller circuit includes STM32F103RET6, wherein the PD0 and PD1 pins of the MCU are connected to an 8MHz crystal oscillator to provide a reference frequency to the STM32 as a clock reference; the PA2 pin of the STM32 F103RET6 in the MCU module is connected to the pin 1 of the operational amplifier chip AD8606 in the front-end circuit.

6. The circuit for detecting electrolyte concentration in body fluid and the signal processing device according to claim 5, characterized in that: The ADC sampling prescaler in the microcontroller circuit is set to 6, the ADC clock frequency is 12MHz, and the ADC sampling time is 55.5 clock cycles.

7. The circuit for detecting electrolyte concentration in body fluid and the signal processing device according to claim 5, characterized in that: The MCU is also used to run the protocol stack program required for Bluetooth communication. After the MCU collects the voltage signal, it is transmitted to the Bluetooth module through USART and the data is broadcast.

8. The circuit for detecting electrolyte concentration in body fluid and the signal processing device according to claim 5, characterized in that: The Bluetooth module includes a receiving end RXD and a transmitting end TXD pin, PA9 is connected to the receiving end RXD pin of the Bluetooth module as a transmitting end, and PA10 is connected to the transmitting end TXD pin of the Bluetooth module as a receiving end.

9. The circuit for detecting electrolyte concentration in body fluid and the signal processing device according to claim 1, characterized in that: The power management circuit includes a boost converter and a buck converter. The boost converter is TPS613222ADBVR, which is used to convert the 3.3V standard voltage into 5V voltage to provide operating voltage for the AD8606 op amp chip; the buck converter is TPS76333DBVR, which is used to convert the 3.7V output voltage of the lithium battery into 3.3V for powering the STM32 and Bluetooth module.

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