CN112180166A - Multi-channel microelectrode bioimpedance testing system and method - Google Patents

Abstract

The invention provides a multichannel microelectrode bioimpedance testing system and method, comprising an MCU control circuit, a multi-stage power supply circuit, a sine wave generating circuit, an attenuator circuit, a measuring circuit, an amplifier circuit, a multi-path ADC conversion circuit, an upper computer communication circuit and a data selector circuit; the circuit design is adopted to apply fine micro-current to the impedance end to be measured to amplify signals through the multistage precision operational amplifier, the MCU control circuit is used for data arrangement and calculation to realize precision measurement of the impedance to be measured, and a multi-channel data selector is integrated to realize multi-channel impedance measurement. The invention realizes the accurate impedance measurement of the multi-channel bioelectrode and meets the requirements of researchers in related fields.

Description

Multi-channel microelectrode bioimpedance testing system and method

Technical Field

The invention belongs to the technical field of biological impedance testing, and particularly relates to a multi-channel microelectrode biological impedance testing system and method.

Background

With the continuous development of biotechnology, human brain research has never been stopped, and currently, brain probe electrodes are continuously developed toward miniaturization, integration and multi-channel, and the most direct measurement standard of the quality of the probe electrodes is the impedance of the electrodes, so that how to rapidly test the impedance of a high-flux electrode array becomes a difficult problem for many researchers. Most of impedance test systems in the market at present are used for testing whether a circuit board meets the production requirements, but not for measuring the impedance of a nerve probe, and cannot meet the requirements of weak current, high flux and automation of the impedance test of the nerve probe.

Disclosure of Invention

The invention aims to provide a multichannel microelectrode bioimpedance testing system and method, which can be used for realizing accurate impedance measurement of a multichannel bioelectrode and meeting the requirements of researchers in related fields.

The invention provides the following technical scheme:

a multichannel microelectrode bioimpedance test system comprises an MCU control circuit, a multi-stage power supply circuit, a sine wave generation circuit, an attenuator circuit, a measurement circuit, an amplifier circuit, a multi-channel ADC conversion circuit, an upper computer communication circuit and a data selector circuit;

the multistage power supply circuit is provided with a multistage filter capacitor array and is used for providing stable and low-noise power supply voltage for the whole system; the sine wave generating circuit comprises a DAC circuit and an operational amplifier circuit, the DAC circuit is electrically connected with the MCU control circuit and used for receiving an instruction of the MCU control circuit to generate a sine wave without a zero crossing point, and the operational amplifier circuit is used for converting the sine wave without the zero crossing point output by the DAC circuit into a zero crossing point sine wave; the attenuator circuit is used for attenuating sine waves of zero-crossing points by twenty-five-hundred times; the measuring circuit is provided with impedance to be measured, and the impedance to be measured is respectively connected with the attenuator circuit and the amplifier circuit; the amplifier circuit is used for amplifying the impedance measurement voltage to be measured to the magnitude which can be accurately collected by the multi-path ADC conversion circuit; the multi-path ADC conversion circuit is connected with the MCU control circuit and is used for sampling original zero-crossing point sine wave data and the measured voltage amplified by the amplifier circuit; the upper computer communication circuit is used for the MCU control circuit to communicate with an upper computer; the data selector circuit is used for the MCU control circuit to select a corresponding measurement channel; and the MCU control circuit is used for scheduling each circuit module and storing the calculated data of the impedance to be measured.

Preferably, the multistage power supply circuit comprises a USB power supply circuit, a power supply circuit and a voltage stabilizing filter circuit which are connected in sequence, and the multistage filter capacitor array comprises a first stage filter capacitor array, a second stage filter capacitor array and a third stage filter capacitor array; the USB power supply circuit is used for supplying USB power to the inside of the system; the power supply circuit is used for boosting and negative pressure of the voltage accessed by the USB power supply circuit after passing through the first-stage filter capacitor array; and the voltage stabilizing filter circuit is used for filtering the voltage boosted and negatively pressurized by the power supply circuit to a stable low-noise power supply voltage to the whole system through the second-stage filter capacitor array and the third-stage filter capacitor array.

Preferably, the operational amplifier circuit is an inverse summation circuit of a single operational amplifier connected to a power supply, and the inverse summation circuit is used for converting a sine wave output by the DAC without a zero crossing point into a sine wave with a zero crossing point; the amplifier circuit adopts rail-to-rail precise operational amplifier and is used for amplifying impedance measurement voltage to the magnitude which can be accurately collected by the multi-path ADC conversion circuit.

Preferably, a pull-up resistor is arranged between each of the sine wave generating circuit and the amplifier circuit and the multi-channel ADC conversion circuit, and the pull-up resistor is used for adjusting the measurement voltage to a range that can be measured by the multi-channel ADC conversion circuit.

Preferably, the data selector circuit comprises 4 ADG1206MUX chips and peripheral circuits thereof, is electrically connected with the MCU control circuit, and is used for the MCU control circuit MCU to select a corresponding measurement channel so as to realize the purpose of multi-channel measurement; the MCU control circuit comprises an STM32F407VGT6 chip and a peripheral circuit thereof, wherein the STM32F407VGT6 chip is connected into the system through a direct plug pin.

A measuring method of a multichannel microelectrode bioimpedance testing system comprises the following steps:

a multi-stage power supply mode is adopted, and a USB power supply is subjected to multi-stage filtering processing to provide stable and low-noise power supply voltage for the whole system;

the MCU control circuit is communicated with an upper computer through an upper computer communication circuit, and the test frequency, the sampling times, the sampling intervals and the number of channels to be tested of the system are set through the upper computer;

the MCU control circuit controls the sine wave generating circuit to generate continuous zero crossing point sine waves when receiving a measuring starting signal sent by the upper computer, the multi-path ADC conversion circuit reads an instantaneous value of the sine waves in real time and sends the value to the MCU in an SPI communication mode, and the MCU directly sends the data to the upper computer through the upper computer communication circuit without processing;

the zero-crossing point sine wave is attenuated by the attenuator circuit by two thousand, five and hundred times and then is connected into the measuring circuit, the amplifier circuit amplifies the voltage divided by the impedance part to be measured in the measuring circuit and outputs the amplified voltage, the pull-up resistor pulls the voltage output by the amplifier circuit to be close to proper positive reference voltage so as to adapt to the measuring range of the ADC measuring circuit, the multi-path ADC conversion circuit reads the instantaneous value of the output voltage in real time and sends the value to the MCU in an SPI communication mode;

the MCU calculates the received voltage value to obtain impedance data to be detected, stores the impedance data and counts the impedance data;

after the system finishes the sampling times set by the upper computer, the MCU sends the voltage measured by the impedance testing part to the upper computer through the communication circuit of the upper computer after taking the root mean square, the upper computer sends a data packet for switching channels after confirming that the voltage is received, when the MCU reads the instruction, the sampling interval time set before is delayed, then the MCU controls the data selector circuit to switch the next channel, and the steps are repeated to measure the resistance to be measured of the channel.

Preferably, the multi-stage power supply mode comprises the following steps: after the USB power supply is connected into the system, the USB power supply firstly passes through the first-stage filter capacitor array, then is connected into the two MC34063 chips for boosting and negative pressure respectively, then passes through the next-stage filter capacitor array again, is connected into the LT1964 and LT1761 chips, and finally is output to the whole system for use after passing through the first-stage filter capacitor array again after respectively outputting +5V and-5V.

Preferably, the method for generating a zero-crossing sine wave comprises the following steps: the MCU control circuit controls 8 GPIO ports connected with a DAC digital-to-analog converter to generate high and low level changes, the change of each GPIO port corresponds to one output of the DAC, after the time sequence that the GPIO ports convert the high and low levels is determined, a sine wave can be generated at the output end of the DAC, the system generates a sine wave of +/-5V meeting the zero crossing point of measurement requirements in a mode that the sine wave output by the DAC and the voltage of +5V generated by the LT1761 are subjected to phase reversal summation through a single operational amplifier, and the multichannel ADC conversion circuit reads the instantaneous value of the sine wave in real time for impedance calculation and transmission to an upper computer for display, so that a user can conveniently check whether the waveform is wrong.

Preferably, the measuring circuit adopts a voltage dividing circuit, and the method for calculating the impedance to be measured includes the following steps: according to ohm's law, the following formula is used:

namely:

the parameters V1 and V2 and the impedance to be measured are complex numbers, the imaginary part of the parameters represents the phase relationship in the circuit, when a known voltage V1 is applied, the V1 is a zero-crossing sine wave after attenuation, and V2 is measured, the V2 is the voltage of the impedance to be measured after being amplified by an access amplifier circuit and then being measured, the impedance to be measured can be calculated according to the formula, and 1M in the formula is a voltage-dividing resistor in a voltage-dividing circuit.

Preferably, after the resistance measurement of all channels to be tested is completed, the MCU enters a standby mode to wait for the upper computer to send a new control packet.

The invention has the beneficial effects that: the test current realized by the system design circuit can be in a nano-ampere level, the electrode can not be damaged while the test is finished, and the system can be directly connected to the inside of a living body for measurement without generating any stimulation; the system adopts a multi-stage power supply for power supply, the generated noise is almost completely eliminated, and the system test performance is provided; the system design can generate a sine alternating current signal of a zero crossing point, filter a direct current component, ensure the normal work of an operational amplifier in a circuit and more effectively transmit voltage conversion information; impedance resolving is facilitated; the data selector circuit has extremely low switching noise, and can realize arbitrary channel selection during design realization; the amplifier circuit realizes high-fidelity amplification of signals and prevents the solved impedance value from generating larger deviation; the invention can provide micro-current and measure the electrode impedance of a plurality of channels at one time, and can be widely applied to the fields of invasive computer interfaces, nerve stimulation, behavior prediction and the like.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

FIG. 1 is a schematic diagram of the system architecture of the present invention;

FIG. 2 is a schematic diagram of a power supply circuit of the present invention;

FIG. 3 is a schematic diagram of a voltage regulation filter circuit of the present invention;

FIG. 4 is a DAC circuit schematic of the sine wave generation circuit of the present invention;

FIG. 5 is a schematic diagram of an inverse summing circuit of the sine wave generation circuit of the present invention;

FIG. 6 is a schematic diagram of an attenuator circuit according to an embodiment of the present invention;

FIG. 7 is a schematic diagram of a measurement circuit of the present invention;

FIG. 8 is a schematic of an amplifier circuit of the present invention;

FIG. 9 is a schematic diagram of a multi-way ADC conversion circuit according to the present invention;

FIG. 10 is a schematic diagram of the host computer communication circuitry of the present invention;

FIG. 11 is a schematic diagram of an MCU control circuit of the present invention;

FIG. 12 is a schematic view of the measurement principle of the present invention;

FIG. 13 is a schematic diagram of a measurement implementation circuit of the present invention;

FIG. 14 is a diagram illustrating a packet format according to an embodiment of the present invention;

FIG. 15 is a schematic flow chart of the method of the present invention.

Detailed Description

As shown in figure 1, a multichannel microelectrode bioimpedance test system comprises an MCU control circuit, a multi-stage power supply circuit, a sine wave generation circuit, an attenuator circuit, a measurement circuit, an amplifier circuit, a multi-path ADC conversion circuit, an upper computer communication circuit and a data selector circuit; the multistage power supply circuit is provided with a multistage filter capacitor array and is used for providing stable and low-noise power supply voltage for the whole system; the sine wave generating circuit comprises a DAC circuit and an operational amplifier circuit, the DAC circuit is electrically connected with the MCU control circuit and used for receiving an instruction of the MCU control circuit to generate a sine wave without a zero crossing point, and the operational amplifier circuit is used for converting the sine wave without the zero crossing point output by the DAC circuit into a zero crossing point sine wave; the attenuator circuit is used for attenuating sine waves of zero-crossing points by twenty-five-hundred times; the measuring circuit is provided with impedance to be measured, and the impedance to be measured is respectively connected with the attenuator circuit and the amplifier circuit; the amplifier circuit is used for amplifying the impedance measurement voltage to be measured to the magnitude which can be accurately acquired by the multi-path ADC conversion circuit; the multi-path ADC conversion circuit is connected with the MCU control circuit and is used for sampling original zero-crossing point sine wave data and the measured voltage amplified by the amplifier circuit; the upper computer communication circuit is used for the MCU control circuit to communicate with the upper computer; the data selector circuit is used for the MCU control circuit to select the corresponding measuring channel; the MCU control circuit is used for scheduling each circuit module and storing the impedance calculation data to be detected. The electrode for monitoring the bioelectricity signals is extremely fine and cannot bear overhigh voltage and current, the testing current designed and realized by the system is in a nanoampere level, the electrode can not be damaged when the testing is finished, and the system is beneficial to the fact that the device can even be directly connected into a living body for measurement and cannot generate any stimulation. The system can measure the impedance of multiple channels in one operation, and meets the requirement of multi-channel electrode impedance test.

As shown in fig. 1-3, the multi-stage power supply circuit includes a USB power supply circuit, a power supply circuit, and a voltage-stabilizing filter circuit, which are connected in sequence; the USB power supply circuit is a conventional USB power supply port and is used for supplying USB power to the inside of the system; the power supply circuit is electrically connected with the USB power supply circuit, is used for boosting a 5V power supply accessed by the USB port to 8.7V and carrying out negative phase of the 5V power supply accessed by the USB port to-8.7V respectively, and then is respectively input to a voltage stabilizing filter circuit corresponding to the next stage for low-noise filtering processing; the voltage stabilizing and filtering circuit, namely an LT1964 and two LT1761 low-noise low-dropout linear voltage regulators and peripheral circuits thereof, is respectively electrically connected with a superior power circuit and is used for filtering +8.7V and-8.7V output by the power circuit to +5V and-5V and then outputting the +5V and-5V to the whole system so as to provide stable low-noise power supply voltage for the whole system, and because the limit of LT1761 output current is 100mA, the system adopts two LT1761 for outputting +5V voltage, and LT1964 for generating-5V voltage to an amplifier circuit used in the system, which theoretically can not reach the current limit value, only one LT is adopted.

Specifically, different from direct power supply of single power supplies of other equipment, the equipment processes a power supply accessed by a USB through five stages, after the power supply of the USB is accessed into the system, the power supply firstly passes through a filter capacitor array of a first stage, then is accessed into two MC34063 to respectively carry out boosting and negative pressure, then passes through a filter capacitor array of a next stage again, is accessed into LT1964 and LT1761 chips, and after the power supply of the USB and the filter capacitor array of the next stage respectively output +5V and-5V, the power supply of the USB passes through the filter capacitor array of the first stage again, and finally can be output to the whole system for use, so that noise generated by the power supply of.

As shown in fig. 4-5, the sine wave generating circuit of the present system is divided into two parts, the first part is a DAC circuit, which is electrically connected to the MCU control circuit, and is used to receive the command from the MCU and generate a sine wave without passing through a zero point by adjusting the amplitude and frequency of the digital-to-analog conversion (a sine wave with a zero crossing point cannot be directly generated due to the DAC limitation). Because sine waves without zero crossing points bring direct current offset to a measuring circuit and greater noise filtering difficulty, zero crossing point processing of the next stage is required; the second part is a zero-crossing point sine wave circuit which is realized by combining a single operational amplifier with a sine wave which does not pass through a zero point at the previous stage, and the zero-crossing point sine wave circuit converts the sine wave which does not pass through the zero point and is output by the DAC into the sine wave which passes through the zero point in a mode of carrying out inverted summation after +5V is accessed.

As shown in fig. 6, the attenuator circuit adopted in the present system, that is, a resistor connected in series with a human circuit and a T-type grounded resistor, has a resistance value measured according to a specific circuit, the resistance value in the schematic diagram is only used as an example for realizing 2500 times attenuation of a zero-crossing point sine wave, and the circuit shown in fig. 6 corresponds to R2 and R3 resistors therein.

As shown in fig. 7, the measuring circuit of the system may be composed of a voltage dividing resistor and an impedance to be measured, and the voltage on the impedance to be measured is measured for a plurality of times by applying a known sine wave voltage (i.e. the sine wave generated by the sine wave generating circuit and attenuated) to the two, and finally the impedance to be measured is accurately measured after the root mean square of the measured values is taken for a plurality of times.

As shown in fig. 8, the amplifier circuit of the present system may employ TLC2272AC and TS922 rail-to-rail precision op-amps, which are used to amplify the impedance measurement voltage to a level that the ADC can accurately acquire. The amplifier circuit selects high-performance rail-to-rail precision operational amplifier for realizing high-fidelity signal amplification and preventing the calculated impedance value from generating larger deviation.

As shown in fig. 1 and 9, the multi-channel ADC conversion circuit of the system may adopt an AD7606-4ADC conversion chip and its peripheral circuit, which are connected and communicated with the MCU control circuit through the SPI port, for sampling the original sine wave data and the amplified measurement voltage. Furthermore, a pull-up resistor, namely an ADC measuring end, is connected in parallel to a 5V 10K ohm resistor, which is used for pulling up the ADC measuring voltage which originally oscillates near the zero point to oscillate near 2.5V, so as to facilitate data calculation and adjust the measuring voltage to the range where the ADC can measure.

As shown in fig. 10, the communication circuit of the upper computer of the system adopts a CH340GUSB serial port conversion chip and a peripheral circuit thereof, which are electrically connected with the MCU control circuit, and the serial port communication between the MCU and the PC terminal can be realized by accessing the MCU serial port line to the corresponding serial port on the chip.

As shown in fig. 11, the MCU control circuit of the system employs STM32F407VGT6 and its peripheral circuits, which are connected to the system via a pin for scheduling other circuit modules, so as to ensure normal operation of the whole system and preliminary processing of data, and facilitate plugging and unplugging, and upgrade firmware or troubleshooting of the whole system. The data selector circuit, namely the 4 ADG1206MUX chips and the peripheral circuits thereof, is electrically connected with the MCU control circuit, can select the corresponding measuring channel by the MCU, has extremely low switching noise, and can realize any channel selection during design realization. Furthermore, the MCU control circuit is detachably designed, so that the later function expansion and chip computing power upgrading are facilitated.

As shown in fig. 12 and fig. 13, in the measurement principle of the multi-channel microelectrode bioimpedance test system, the MCU control circuit controls the sine wave generating circuit to generate a sine ac signal that passes through the zero point after continuous modulation, the multi-channel ADC conversion circuit reads the instantaneous value of the sine ac signal at the zero point in real time and sends the value to the MCU; meanwhile, the sinusoidal alternating current signal of the zero crossing point is attenuated by twenty-five-hundred times by the attenuator circuit and then is connected to the measuring circuit, the amplifier circuit amplifies the divided voltage of the impedance part to be measured and outputs the amplified voltage, the pull-up resistor pulls the voltage output by the amplifier circuit from the vicinity of 0V to the vicinity of 2.5V for oscillation, the ADC measuring circuit does not access a negative voltage reference, so that the measured value needs to be pulled up to the vicinity of a proper positive reference voltage to adapt the range of the ADC measuring circuit, and the multichannel ADC converting circuit reads the instantaneous value of the multichannel ADC converting circuit in real time and sends the read value to the MCU; the MCU control circuit synthesizes the voltage data collected by the ADC measuring circuit and calculates the impedance to be measured.

A measuring method of a multichannel microelectrode bioimpedance testing system comprises the following steps:

a multi-stage power supply mode is adopted, and a USB power supply is subjected to multi-stage filtering processing to provide stable and low-noise power supply voltage for the whole system;

the MCU control circuit is communicated with an upper computer through an upper computer communication circuit, and the test frequency, the sampling times, the sampling intervals and the number of channels to be tested of the system are set through the upper computer;

the MCU control circuit controls the sine wave generating circuit to generate continuous zero crossing point sine waves when receiving a measuring starting signal sent by the upper computer, the multi-path ADC conversion circuit reads an instantaneous value of the sine waves in real time and sends the value to the MCU in an SPI communication mode, and the MCU directly sends the data to the upper computer through the upper computer communication circuit without processing;

the zero-crossing point sine wave is attenuated by the attenuator circuit by two thousand, five and hundred times and then is connected into the measuring circuit, the amplifier circuit amplifies the voltage divided by the impedance part to be measured in the measuring circuit and outputs the amplified voltage, the pull-up resistor pulls the voltage output by the amplifier circuit to be close to proper positive reference voltage so as to adapt to the measuring range of the ADC measuring circuit, the multi-path ADC conversion circuit reads the instantaneous value of the output voltage in real time and sends the value to the MCU in an SPI communication mode;

the MCU calculates the received voltage value to obtain impedance data to be detected, stores the impedance data and counts the impedance data;

after the system finishes the sampling times set by the upper computer, the MCU sends the voltage measured by the impedance testing part to the upper computer through the communication circuit of the upper computer after taking the root mean square, the upper computer sends a data packet for switching channels after confirming that the voltage is received, when the MCU reads the instruction, the sampling interval time set before is delayed, then the MCU controls the data selector circuit to switch the next channel, and the steps are repeated to measure the resistance to be measured of the channel.

In particular, as shown in fig. 15, the measurement process includes the following steps:

1) the equipment is started, and the power supply circuit and the voltage stabilizing filter circuit work to provide stable working voltage for each device;

(1-1) it needs to be stated that, this system has adopted the mode of the power supply of the multistage power, because the measuring current that this system adopts is minimum (nanoampere level), so the noise factor of the mains voltage has the very big influence to the performance of this system, this system uses two MC34063 circuits to boost +5V voltage that USB inputs to +8.7V and reverse to-8.7 respectively at first, after filtering through the multistage capacitance, input to two LT1761 and one LT1964 chips in order to produce the 5V power output of stable low noise, after filtering through the multistage capacitance again, can output and supply power to every device;

2) the MCU initializes system software and hardware resources, sends a handshake packet (namely a sending packet with a specified format shown in FIG. 14) to the upper computer through the communication circuit of the upper computer, and the upper computer receives and recognizes the packet header with the format to determine that the lower computer is working, transmits a working state signal to the upper computer and waits for the upper computer to transmit a response packet to perform the next operation;

(2-1) only the interaction mode of the upper computer and the lower computer (MCU control circuit) is explained here, and the format and length of a specific data packet (a sending packet and a response packet are collectively called as a data packet) need to be modified correspondingly according to the use occasion;

3) the user sets the test frequency, sampling times, sampling intervals and the number of channels to be tested of the system on the upper computer. The upper computer informs the lower computer of the specific parameters of the tasks to be executed through a response packet transmitted at regular time (transmitted to the lower computer once every 10 ms);

(3-1) the test frequency determines the frequency of sampling the voltage of the impedance to be measured by a lower computer (MCU control circuit) per second, the unit of the parameter is Hertz, the highest value is 5000HZ (namely 5000 times of reading measurement data per second), and the lowest value is 1HZ (namely 1 time of reading measurement data per second); the sampling frequency refers to how many times the voltage of the impedance end to be measured needs to be measured after one measurement is completed (the root mean square of the multiple sampling results needs to be obtained after one measurement is completed), and under the condition that the test frequency is fixed, the sampling frequency is increased to improve the measurement accuracy, but the measurement time of each channel is prolonged. Conversely, reducing the sampling times can shorten the measurement time of each channel, but can also sacrifice certain measurement accuracy; the test frequency and the sampling times jointly determine the time required for measuring the impedance of each channel, and the specific relationship can be determined by the formula:

the sampling interval refers to a period of time after each measurement of one channel is completed, in order to ensure that the circuit jump interference generated when the data selector switches channels disappears or becomes small enough, the system needs to wait for the next channel to start measurement. The number of channels to be tested, namely the number of all channels to be measured in the measurement, the system supports continuous measurement of 64 channels at most, and any channel number measurement smaller than or equal to 64 is allowed in the system.

4) When receiving a measurement starting signal sent by an upper computer, the MCU firstly controls the sine wave generating circuit to generate continuous sine waves, the multi-path ADC conversion circuit reads an instantaneous value of the sine waves in real time and sends the value to the MCU in an SPI communication mode, and the MCU directly sends the data to the upper computer through the upper computer communication circuit without processing;

(4-1) the method for generating the sine wave comprises the steps that the MCU control circuit controls 8 GPIO ports connected with a DAC to generate high and low level changes, the change of each GPIO port corresponds to one output of the DAC, and after the time sequence of the GPIO ports for converting the high and low levels is determined, the sine wave can be generated at the output end of the DAC. Because the DAC can not output negative voltage, the sine wave generated by the method can not be directly applied to the impedance to be measured (if the sine wave does not pass through zero, a direct current component is introduced into the circuit, the component is very easy to be interfered by external noise, and once the interference occurs, the precision degree of a test result can be greatly influenced by the minimum measurement voltage and measurement current adopted by the system after the interference is amplified by an amplifier circuit), the system generates a sine wave of +/-5V of a zero crossing point which meets the measurement requirement by carrying out inverse summation on the sine wave output by the DAC and the voltage of +5V generated by the LT1761 through a single operational amplifier; the multichannel ADC conversion circuit reads the instantaneous value of the sine wave in real time, is used for later impedance calculation (see 6-1 in detail) and transmits the value to an upper computer for displaying, and is convenient for a user to check whether the waveform is wrong;

the sine wave generated by the system is a sine alternating current signal which passes through a zero point after being modulated, and because the method filters out a direct current component, the normal work of an operational amplifier in a circuit can be ensured, voltage transformation information can be transmitted more effectively, and the subsequent impedance calculation is facilitated.

5) The sine wave is connected to the measuring circuit after passing through the attenuator circuit;

(5-1) the attenuator circuit consists of two resistors, and the resistance value of the attenuator circuit is determined according to the resistance value of a divider resistor matched with the impedance to be measured and is used for realizing the two thousand, five and hundred times of attenuation of the zero-crossing sine wave;

6) the amplifier circuit amplifies the voltage divided by the impedance part to be detected and outputs the amplified voltage;

(6-1) the method for measuring impedance of the device mainly relies on a simple voltage division circuit, the circuit principle of which is shown in fig. 7, and the parameters of the circuit can be determined by the following formula according to ohm's law:

namely:

the formula can be generalized to an alternating current sinusoidal signal, that is, the parameters V1 and V2 and the impedance to be measured are complex numbers, and the imaginary part of the complex numbers represents the phase relation in the circuit. When a known voltage V1 (i.e., the zero-crossing sine wave after the attenuation) is applied and V2 (i.e., the voltage of the impedance to be measured after the impedance to be measured is amplified by the access amplifier circuit) is measured, the impedance to be measured can be solved according to the formula;

7) the pull-up resistor pulls up the voltage output by the amplifier circuit from the oscillation of 0V to the oscillation of 2.5V;

(7-1) since the ADC measurement circuit does not access the negative voltage reference, it is necessary to pull up the above measurement value to around the appropriate positive reference voltage to adapt the range of the ADC measurement circuit;

8) the multichannel ADC conversion circuit reads the instantaneous value of the multichannel ADC conversion circuit in real time and sends the value to the MCU in a SPI communication mode;

9) the MCU stores and counts the received impedance data to be detected, and the system is maintained to continuously operate;

10) after the sampling times set by the upper computer are finished, the MCU sends the voltage measured by the impedance testing part to the upper computer through the communication circuit of the upper computer after the voltage is taken as the root mean square;

11) the upper computer confirms that the data packet of the channel is sent after receiving, when the MCU reads the instruction, the MCU delays the sampling interval time set before, then controls the data selector circuit to switch the next channel, and repeats the steps 1) to 10) to measure the resistance to be measured of the channel;

12) after the resistance measurement of all channels needing to be tested is completed, the MCU enters a standby mode, and waits for the upper computer to send a new control packet, and the multichannel impedance measurement in a complete process is finished.

The system method applies extremely fine micro-current to an impedance end to be measured through an impedance resolving function popularized to a complex plane, then amplifies signals through a multi-stage precise operational amplifier, and finally carries out data arrangement and calculation through the MCU so as to realize precise measurement of the impedance to be measured. Meanwhile, multi-channel impedance measurement is realized by integrating a multi-channel data selector in the circuit.

Although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A multichannel microelectrode bioimpedance test system is characterized by comprising an MCU control circuit, a multi-stage power supply circuit, a sine wave generation circuit, an attenuator circuit, a measuring circuit, an amplifier circuit, a multi-path ADC conversion circuit, an upper computer communication circuit and a data selector circuit;

the multistage power supply circuit is provided with a multistage filter capacitor array and is used for providing stable and low-noise power supply voltage for the whole system; the sine wave generating circuit comprises a DAC circuit and an operational amplifier circuit, the DAC circuit is electrically connected with the MCU control circuit and used for receiving an instruction of the MCU control circuit to generate a sine wave without a zero crossing point, and the operational amplifier circuit is used for converting the sine wave without the zero crossing point output by the DAC circuit into a zero crossing point sine wave; the attenuator circuit is used for attenuating sine waves of zero-crossing points by twenty-five-hundred times; the measuring circuit is provided with impedance to be measured, and the impedance to be measured is respectively connected with the attenuator circuit and the amplifier circuit; the amplifier circuit is used for amplifying the impedance measurement voltage to be measured to the magnitude which can be accurately collected by the multi-path ADC conversion circuit; the multi-path ADC conversion circuit is connected with the MCU control circuit and is used for sampling original zero-crossing point sine wave data and the measured voltage amplified by the amplifier circuit; the upper computer communication circuit is used for the MCU control circuit to communicate with an upper computer; the data selector circuit is used for the MCU control circuit to select a corresponding measurement channel; and the MCU control circuit is used for scheduling each circuit module and storing the calculated data of the impedance to be measured.

2. The multi-channel microelectrode bioimpedance test system of claim 1, wherein the multi-stage power supply circuit comprises a USB power supply circuit, a power supply circuit and a voltage stabilizing filter circuit, which are connected in sequence, and the multi-stage filter capacitor array comprises a first stage filter capacitor array, a second stage filter capacitor array and a third stage filter capacitor array; the USB power supply circuit is used for supplying USB power to the inside of the system; the power supply circuit is used for boosting and negative pressure of the voltage accessed by the USB power supply circuit after passing through the first-stage filter capacitor array; and the voltage stabilizing filter circuit is used for filtering the voltage boosted and negatively pressurized by the power supply circuit to a stable low-noise power supply voltage to the whole system through the second-stage filter capacitor array and the third-stage filter capacitor array.

3. The multi-channel microelectrode bioimpedance test system of claim 1, wherein the operational amplifier circuit is an inverse summation circuit with a single operational amplifier connected to a power supply, and the inverse summation circuit is used for converting sine waves without zero crossing points output by the DAC into sine waves with zero crossing points; the amplifier circuit adopts rail-to-rail precise operational amplifier and is used for amplifying impedance measurement voltage to the magnitude which can be accurately collected by the multi-path ADC conversion circuit.

4. The multi-channel microelectrode bioimpedance test system of claim 1, wherein a pull-up resistor is disposed between each of the sine wave generation circuit and the amplifier circuit and the multi-channel ADC conversion circuit, and the pull-up resistor is used for adjusting the measurement voltage to a range that can be measured by the multi-channel ADC conversion circuit.

5. The multi-channel microelectrode bioimpedance test system of claim 1, wherein the data selector circuit comprises 4 ADG1206MUX chips and peripheral circuits thereof, electrically connected to the MCU control circuit, and used for the MCU control circuit to select the corresponding measurement channel for multi-channel measurement; the MCU control circuit comprises an STM32F407VGT6 chip and a peripheral circuit thereof, wherein the STM32F407VGT6 chip is connected into the system through a direct plug pin.

6. A measuring method of a multichannel microelectrode bioimpedance testing system is characterized by comprising the following steps:

a multi-stage power supply mode is adopted, and a USB power supply is subjected to multi-stage filtering processing to provide stable and low-noise power supply voltage for the whole system;

the MCU control circuit is communicated with an upper computer through an upper computer communication circuit, and the test frequency, the sampling times, the sampling intervals and the number of channels to be tested of the system are set through the upper computer;

the MCU control circuit controls the sine wave generating circuit to generate continuous zero crossing point sine waves when receiving a measuring starting signal sent by the upper computer, the multi-path ADC conversion circuit reads an instantaneous value of the sine waves in real time and sends the value to the MCU in an SPI communication mode, and the MCU directly sends the data to the upper computer through the upper computer communication circuit without processing;

the zero-crossing point sine wave is attenuated by the attenuator circuit by two thousand, five and hundred times and then is connected into the measuring circuit, the amplifier circuit amplifies the voltage divided by the impedance part to be measured in the measuring circuit and outputs the amplified voltage, the pull-up resistor pulls the voltage output by the amplifier circuit to be close to proper positive reference voltage so as to adapt to the measuring range of the ADC measuring circuit, the multi-path ADC conversion circuit reads the instantaneous value of the output voltage in real time and sends the value to the MCU in an SPI communication mode;

the MCU calculates the received voltage value to obtain impedance data to be detected, stores the impedance data and counts the impedance data;

after the system finishes the sampling times set by the upper computer, the MCU sends the voltage measured by the impedance testing part to the upper computer through the communication circuit of the upper computer after taking the root mean square, the upper computer sends a data packet for switching channels after confirming that the voltage is received, when the MCU reads the instruction, the sampling interval time set before is delayed, then the MCU controls the data selector circuit to switch the next channel, and the steps are repeated to measure the resistance to be measured of the channel.

7. The measurement method of the multi-channel microelectrode bioimpedance test system of claim 6, wherein the multi-stage power supply mode comprises the following steps: after the USB power supply is connected into the system, the USB power supply firstly passes through the first-stage filter capacitor array, then is connected into the two MC34063 chips for boosting and negative pressure respectively, then passes through the next-stage filter capacitor array again, is connected into the LT1964 and LT1761 chips, and finally is output to the whole system for use after passing through the first-stage filter capacitor array again after respectively outputting +5V and-5V.

8. The measurement method of the multi-channel microelectrode bioimpedance test system according to claim 6, wherein the method for generating the zero-crossing sine wave comprises the following steps: the MCU control circuit controls 8 GPIO ports connected with a DAC digital-to-analog converter to generate high and low level changes, the change of each GPIO port corresponds to one output of the DAC, after the time sequence that the GPIO ports convert the high and low levels is determined, a sine wave can be generated at the output end of the DAC, the system generates a sine wave of +/-5V meeting the zero crossing point of measurement requirements in a mode that the sine wave output by the DAC and the voltage of +5V generated by the LT1761 are subjected to phase reversal summation through a single operational amplifier, and the multichannel ADC conversion circuit reads the instantaneous value of the sine wave in real time for impedance calculation and transmission to an upper computer for display, so that a user can conveniently check whether the waveform is wrong.

9. The measuring method of the multi-channel microelectrode bioimpedance testing system of claim 6, wherein the measuring circuit is a voltage divider circuit, and the method for calculating the impedance to be measured comprises the following steps: according to ohm's law, the following formula is used:

namely:

the parameters V1 and V2 and the impedance to be measured are complex numbers, the imaginary part of the parameters represents the phase relationship in the circuit, when a known voltage V1 is applied, the V1 is a zero-crossing sine wave after attenuation, and V2 is measured, the V2 is the voltage of the impedance to be measured after being amplified by an access amplifier circuit and then being measured, the impedance to be measured can be calculated according to the formula, and 1M in the formula is a voltage-dividing resistor in a voltage-dividing circuit.

10. The measuring method of the multi-channel microelectrode bioimpedance testing system of claim 6, wherein after the resistance measurement of all channels to be tested is completed, the MCU enters a standby mode to wait for the upper computer to send a new control packet.

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