CN205215225U - Human impedance measuring circuit - Google Patents

Abstract

The human body impedance measurement circuit belongs to the field of human body impedance measurement. The technical problem to be solved is: the hardware design of the existing human body impedance analysis measuring instrument is complicated and the development cost is high. The technical points are: the controller controls the multi-frequency signal generating circuit to generate an AC voltage signal, The AC voltage signal is converted into the corresponding excitation current signal by the signal conversion circuit, the excitation current signal is input to the excitation electrode, and thus the voltage signal of the measurement electrode is obtained; the multi-way selection switch is controlled by the controller, and the excitation current loop and the measurement Voltage loop selection. The effect is: the transmission of data through WIFI solves the trouble of relying on computers or LCDs installed on measuring devices to display data, and effectively reduces costs; small size, low cost, easy to carry, and easier to enter the working people's In the family; the choice of eight-electrode measurement and MAX14778 chip makes the circuit design simple and the measurement more accurate.

Description

Human body impedance measurement circuit

technical field

The utility model relates to the field of human body impedance measurement and relates to a human body impedance measurement circuit and a human body impedance measurement device for transmitting measurement data through WIFI.

Background technique

Bio-impedance is closely related to human physiology and pathology, so bio-impedance measurement technology is constantly improving, and various human body impedance analyzers appear. Although the current human body impedance measurement devices can accurately measure the impedance values of various sections of the human body, their hardware design is complicated, the volume is large, the development cost is high, and the price is expensive, so it is difficult to enter the families of the working people. It can only be seen in some large and medium-sized medical institutions; and the existing human body impedance analyzer does not have the function of wireless data transmission, so users cannot carry out real-time and effective control and management of the device through handheld terminals such as mobile phones and PADs, which is difficult. Meet the needs of modern users to freely control the measurement device anytime, anywhere.

Utility model content

In order to solve the technical problems of complex hardware design and high development cost of existing human body impedance analysis measuring instruments, the utility model provides a human body impedance measurement circuit, which realizes measurement data transmission based on WIFI, forming a remote transmission of data. The human body impedance measuring device has a compact circuit structure, simple hardware implementation, small size, convenient portability and strong practicability.

In order to achieve the above purpose, the technical solution used in the utility model is: a human body impedance measurement circuit, including a controller, a multi-frequency signal generation circuit, a signal conversion circuit, an excitation electrode, a measurement electrode, a multiplex switch, and a standard reference resistor;

The controller controls the multi-frequency signal generating circuit to generate an AC voltage signal, which is converted into a corresponding excitation current signal by the signal conversion circuit, and the excitation current signal is input to the excitation electrode, and thus the voltage signal of the measurement electrode is obtained; the multi-channel The selection switch is controlled by the controller to select the excitation current loop and the measurement voltage loop; in any excitation current loop, one end of the standard reference resistor is connected in series with the excitation current loop, and the other end of the standard reference resistor is grounded.

Further, the human body impedance measurement circuit also includes a weak voltage signal amplifying circuit, a filter circuit, an effective value detection circuit, and an analog-to-digital conversion circuit connected sequentially, the measuring electrodes are connected to the weak voltage signal amplifying circuit, and the amplifying circuit The digital conversion circuit is connected with the controller signal.

Further, the controller is also connected to the wireless communication module with signals.

Further, the analog-to-digital conversion circuit is also signal-connected with the body weight measurement circuit.

Further, the controller uses STM32F103 chip as the main control chip, the multi-frequency signal generation circuit uses AD9850 as the frequency generation chip, and the signal conversion circuit uses current feedback operational amplifier AD844 to feed back the input voltage amplitude.

Further, the multiplexer uses two MAX14778 dual-channel 4:1 analog multiplexers, and the selected channels are drawn out as excitation electrodes and measurement electrodes respectively.

Further, the resistance value of the standard reference resistor is 1000 ohms.

Further, the weak voltage signal amplification circuit uses AD8221ARM and LTC6910 to extract and amplify weak voltage signals, and the filter circuit uses LTC1560 chip to filter out high-frequency noise.

Further, the effective value detection circuit uses AD637JR to extract the effective value of the signal.

Further, the wireless communication module is a WM-G-MR-09 WIFI module or an ESP8266 serial port to WIFI module or other WIFI modules.

The beneficial effects of the utility model are: the human body impedance measuring circuit has a compact circuit structure, simple hardware implementation, strong practicability, and the user can manage and control the measuring circuit through a wireless communication module.

Description of drawings

Fig. 1 is the structural representation of the human body impedance measuring circuit of the present utility model;

Fig. 2 is a schematic diagram of the connection between the measuring electrode and the human body;

Fig. 3 is a schematic diagram of the communication between the human body impedance measurement circuit and the mobile phone terminal in the embodiment.

detailed description

Embodiment 1: in conjunction with Fig. 1 and Fig. 2, the present embodiment provides a kind of human body impedance measurement circuit, comprises controller 2, multi-frequency signal generation circuit 3, signal conversion circuit 4, excitation electrode 5, measurement electrode 6, multiplex Selector switch 7, standard reference resistor 8, weak voltage signal amplification circuit 9, filter circuit 10, effective value detection circuit 11, analog-to-digital conversion circuit 12;

The controller 2 controls the multi-frequency signal generating circuit 3 to generate an AC voltage signal, and the AC voltage signal is converted into a corresponding excitation current signal by the signal conversion circuit 4, and the excitation current signal is input to the excitation electrode 5, and thus the measurement electrode 6 is obtained. voltage signal; the multi-way selector switch 7 is controlled by the controller 2 to select the excitation current loop and the measurement voltage loop; in any excitation current loop, one end of the standard reference resistor 8 is connected in series in the excitation current loop, and the other end of the standard reference resistor One end is grounded.

Weak voltage signal amplifying circuit 9, filter circuit 10, effective value detection circuit 11, and analog-to-digital conversion circuit 12 are sequentially connected to each other, the measuring electrode 6 is connected to weak voltage signal amplifying circuit 9, and the analog-to-digital conversion circuit 12 is connected to controller 2. .

Each part of the measuring circuit is powered by a power supply 1 . Wherein, the controller can be a single-chip microcomputer, and the analog-to-digital conversion circuit 12 can be an external circuit connected to the single-chip microcomputer, or an AD inside the single-chip microcomputer can be used, that is, the actual circuit is realized by directly connecting the signal line with the corresponding pin of the single-chip microcomputer.

In the measurement circuit of this embodiment, the impedance of the human body is equivalent to a five-segment impedance model of the trunk and limbs. The four excitation electrodes of the measurement circuit are respectively in contact with the left and right wrists and the left and right forefoot of the human body. The four voltage measurement electrodes of the measurement circuit are respectively connected to the left and right sides. The palms of the hands touch the heels of the left and right feet. One way to measure body impedance using the measurement circuit described is:

S1: The controller controls the multi-frequency signal generating circuit to send out an AC voltage signal with an initial frequency of 10kHZ.

S2: The AC voltage signal is converted into a human body safety excitation current signal whose effective value is less than 100uA through the signal conversion circuit.

S3: Under the control of the controller, it is selected by the multi-way switch pair and the excitation current loop and the measurement voltage loop. The measurement channels at each frequency are:

The excitation current forms loop 1 through I1-R1-R2-I2-R, the measurement loop: V1-V2, and the resistance value of R1+R2 can be obtained according to the value of the reference resistor R;

The excitation current forms loop 2 through I3-R3-R4-I4-R, the measurement loop: V3-V4, and the resistance value of R3+R4 can be obtained according to the value of the reference resistor R;

The excitation current forms loop 3 through I1-R1-R5-R3-I3-R, the measurement loop: V1-V3, and the resistance value of R1+R5+R3 can be obtained according to the value of the reference resistor R;

The excitation current forms loop 4 through I2-R2-R5-R4-I4-R, the measurement loop: V2-V4, and the resistance value of R2+R5+R4 can be obtained according to the value of the reference resistor R;

The excitation current forms loop 5 through I1-R1-R5-R4-I4-R, the measurement loop: V1-V4, and the resistance value of R1+R5+R4 can be obtained according to the value of the reference resistor R.

S4. In each measurement circuit, under the control of the controller, the measurement electrode measures the voltage value of the equivalent impedance of each section of the human body in a timely manner, and performs amplification, filtering and effective value detection;

S5: The analog-to-digital conversion circuit performs analog-to-digital conversion on the measured voltage signals of each measuring electrode, and calculates and corrects them, and finally obtains accurate impedance values of each segment of the human body. The calculation of the impedance value is completed by the controller. The calculated data comes from the resistance value of the above-mentioned reference resistor and the measured voltage, that is, 5 linearly independent equations and 5 unknowns can be obtained from the above, and the resistance values of R1~R5 can be calculated.

S6: Change the frequency value, and continue the measurement according to the above steps.

Embodiment 2: have the technical scheme identical with embodiment 1, more specifically, controller 2 in the present embodiment is also connected with wireless communication module 13 signals, preferably, this wireless communication module 13 is a WIFI module, and Using this wireless communication module, after the measurement is completed, the controller executes the algorithm to obtain the equivalent impedance value of each part of the human body, which can be directly transmitted from the measurement circuit to the device terminal, and the corresponding display program is set at the device terminal to measure The data can be transmitted to the user terminal through the wireless communication module and displayed.

Add the wireless communication module, when using the measurement circuit, first use the mobile phone to search for the signal R_TEST to initialize the signal, and then connect to the signal after entering the password; after the connection is successful, open the impedance measurement software on the mobile phone and select the measurement method; in this embodiment Two measurement methods are given: frequency selective measurement and automatic measurement. Taking automatic measurement as an example, the default start frequency of the system is 10kHZ, the step size is 5kHZ, and the stop frequency is 100kHZ.

In addition, the corresponding software can also be used in the terminal equipment to control the control of the multi-frequency signal generation circuit by the controller, so that the tester can connect his mobile phone, PAD and other handheld mobile terminals to the wireless communication module, and then open the corresponding application software and select the measurement method, the controller can control the multi-frequency signal generating circuit to generate the AC voltage signal according to the measurement method selected by the user, or select the default frequency output. The measurement circuit in this embodiment greatly facilitates the tester's control and management of the test, and improves the test experience. The use of terminal handheld devices does not require the cooperation of computers or LCD touch screens, greatly reducing development costs, and the measurement circuit can be more conveniently and widely used in body composition analysis, human blood flow diagram measurement, gastric motility Clinical and research fields based on human body impedance characteristics such as medical detection, and the hardware design of the measurement circuit in this embodiment is simple, the cost of hardware and software is relatively low, and the market prospect is good.

Embodiment 3: have the technical scheme identical with embodiment 1 or 2, more specifically, described analog-to-digital conversion circuit 12 is also connected with body weight measurement circuit 14 signals, gathers body weight measurement data, when human body impedance analysis, As reference data, the body weight measurement circuit is a relatively conventional measurement circuit, so it will not be described in detail here. Wherein, the analog-to-digital conversion circuit 12 can be an external circuit connected with the single-chip microcomputer, or the internal AD of the single-chip microcomputer can be used, that is, the actual circuit is It is realized by directly connecting the signal line with the corresponding pin of the microcontroller.

Embodiment 4: have the same technical solution as embodiment 1 or 2 or 3, more specifically, this embodiment carries out type selection for each component involved in the technical solution in embodiment 1 or 2 or 3 or : described controller 2 uses STM32F103 chip as main control chip, and described multi-frequency signal generation circuit 3 takes AD9850 as frequency generation chip, and described signal conversion circuit 4 uses current feedback operational amplifier AD844 to input voltage amplitude feedback . The multiplexer 7 adopts 2 slices of MAX14778 dual-channel 4:1 analog multiplexer, and the selected channels are drawn out as the excitation electrode 5 and the measurement electrode 6 respectively. The selection of this chip does not need to increase the ESD The protection circuit makes the circuit structure more compact and the circuit volume smaller. The resistance value of the standard reference resistor 8 is 1000 ohms. The weak voltage signal amplifying circuit 9 adopts AD8221ARM and LTC6910 to extract and amplify the weak voltage signal, and the filter circuit 10 adopts LTC1560 chip to filter out high-frequency noise. The effective value detection circuit 11 uses AD637JR to extract the effective value of the signal. Described wireless communication module 13 is WM-G-MR-09 (marvell8686) module or ESP8266 serial port to WIFI module, wherein: the signal that WM-G-MR-09 module sends as AP can only be connected with apple terminal and computer, Choose this module for data transmission with Apple terminal or computer. However, this module does not have corresponding protocol support for Android phones, so it cannot be connected to Android phones. ESP8266 module can realize communication with Android phones. For the wireless communication module selection The model can be adapted to different terminal equipments and covers a wide range.

The measurement circuit provided by this embodiment is small in size, easy to carry and low in cost in terms of circuit design. In terms of data transmission, because it is based on WIFI, the transmission is more convenient. In terms of measurement accuracy, due to the use of 8 electrodes, it can Eliminate the contact resistance of human skin, and the measurement is more accurate.

The above is only a preferred embodiment of the utility model, but the scope of protection of the utility model is not limited thereto. The equivalent replacement or change of the new technical solution and the concept of the utility model shall be covered by the protection scope of the utility model.

Claims (10)

1. a human body impedance measuring circuit, is characterized in that: comprise controller (2), multiple-frequency signal circuit for generating (3), signaling conversion circuit (4), exciting electrode (5), measurement electrode (6), multidiameter option switch (7), canonical reference resistance (8);

Controller (2) controls multiple-frequency signal circuit for generating (3) and produces ac voltage signal, this ac voltage signal is converted to corresponding exciting current signal by signaling conversion circuit (4), this exciting current signal inputs to exciting electrode (5), and obtains the voltage signal of measurement electrode (6) thus; Multidiameter option switch (7) is controlled by controller, to exciting current loop and measuring voltage loop choice; In arbitrary exciting current loop, canonical reference resistance (8) one end is serially connected in this exciting current loop, and the other end ground connection of canonical reference resistance (8).

2. human body impedance measuring circuit as claimed in claim 1, it is characterized in that, also comprise light current pressure signal amplification circuit (9), filter circuit (10), RMS to DC circuit (11), analog to digital conversion circuit (12) that signal successively connects, measurement electrode (6) and light current press signal amplification circuit (9) signal to be connected, and analog to digital conversion circuit (12) is connected with controller (2) signal.

3. human body impedance measuring circuit as claimed in claim 1, it is characterized in that, described controller (2) is also connected with wireless communication module (13) signal.

4. human body impedance measuring circuit as claimed in claim 2, it is characterized in that, described analog to digital conversion circuit (12) is also connected with measured body weight circuit (14) signal.

5. human body impedance measuring circuit as claimed in claim 1, it is characterized in that, described controller (2) is using STM32F103 chip as main control chip, described multiple-frequency signal circuit for generating (3) take AD9850 as frequency generation chip, and described signaling conversion circuit (4) operating amplifier with current feedback AD844 feeds back input voltage amplitude.

6. human body impedance measuring circuit as claimed in claim 1, it is characterized in that: described multidiameter option switch (7) adopts 2 MAX14778 dual pathways 4:1 analog multiplexers, and selector channel is drawn as exciting electrode (5) and measurement electrode (6).

7. human body impedance measuring circuit as claimed in claim 1, is characterized in that: the resistance of described canonical reference resistance (8) is 1000 ohm.

8. human body impedance measuring circuit as claimed in claim 2, it is characterized in that: described light current pressure signal amplification circuit (9) adopts AD8221ARM and LTC6910 extract and amplify weak voltage signal, described filter circuit (10) adopts LTC1560 chip filter away high frequency noise.

9. human body impedance measuring circuit as claimed in claim 2, is characterized in that: described RMS to DC circuit (11) adopts AD637JR to extract the virtual value of signal.

10. human body impedance measuring circuit as claimed in claim 3, is characterized in that: described wireless communication module (13) turns WIFI module or other WIFI module or other wireless communication modules for WM-G-MR-09WIFI module or ESP8266 serial ports.