CN103698607A - Impedance-spectrum measuring system based on wireless digital electrode - Google Patents
Impedance-spectrum measuring system based on wireless digital electrode Download PDFInfo
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- CN103698607A CN103698607A CN201310700343.4A CN201310700343A CN103698607A CN 103698607 A CN103698607 A CN 103698607A CN 201310700343 A CN201310700343 A CN 201310700343A CN 103698607 A CN103698607 A CN 103698607A
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Abstract
The invention relates to an impedance-spectrum measuring system based on a wireless digital electrode. The impedance-spectrum measuring system is formed by sequentially connecting a digital electrode, a single chip microcomputer, a wireless module and an upper computer, wherein the digital electrode comprises an electrode array, a digital switch, an AD5933 and a peripheral circuit of the AD5933, an ATmega16 single chip microcomputer of the Atmel company is adopted as the single chip microcomputer, and an NRF24L01 radio-frequency transceiver of the Nordic VLSI company is selected as the wireless module and works at the ISM frequency band of 2.4 to 2.5GHz. Compared with a previous system, the integrated-type impedance-measuring chip AD5933 is adopted by the impedance-spectrum measuring system based on the wireless digital electrode designed by the invention, the circuit expansion of the integrated-type impedance-measuring chip AD5933 is carried out, the digital electrode is designed, and wireless transmission is adopted, so that the impedance-spectrum measuring system has the advantages of simple structure, high integration level, good stability, wide measuring range, convenience in carrying and the like.
Description
Technical field
The invention belongs to biomedical engineering and commercial measurement field, the impedance spectrum that is specifically related to the tested field domain of closed edge inside is measured, especially a kind of impedance spectrum measuring system based on wireless digital electrode.
Background technology
Electrical impedance spectrometry technology (Electrical Impedance Spectroscopy, EIS) ultimate principle is to utilize the different medium of the tested field domain of closed edge inside to have different impedance (resistance or electricity are led) characteristic, by applying drive current (voltage), Measured Boundary response voltage (electric current) signal, for rebuilding the resistivity distribution of inside, thing field and the image of variation thereof.The ultimate principle of EIS is to place a circle electrode on the measurand surface of closed edge, voltage or the current signal of data collector output, first by 1 electrode, be applied in measurand, then measure response voltage or current signal on other electrodes, to the impedance information that the voltage and current signal recording amplifies, AD conversion, Fourier transform etc. obtain field domain inside, finally reach host computer and realize data analysis, image reconstruction etc. again.Therefore, impedance spectrum measurement has the advantages such as non-intruding, not damaged, volume are little, with low cost, functional imaging.
But, existing impedance spectrum measuring system is comprised of a plurality of modules conventionally, relates to signal generator (that conventional is Direct Digital Frequency Synthesizers DDS), passage change-over switch, programmable gain amplifier (PGA), low-pass filter (LPF), digital to analog converter (ADC) and signal demodulation module etc.; Between electrode and data collector, adopt cable to be connected, its stray capacitance is unstable, not only affects system signal noise ratio, and has suppressed the raising of exciting signal frequency, affects measuring speed; And the data of system output also adopt wire transmission, these make, and system architecture is complicated, integrated level is low, poor anti jamming capability, be not easy to carry.
Summary of the invention
The object of the invention is to overcome the deficiencies in the prior art part, a kind of high integration, strong, the portable impedance spectrum measuring system based on wireless digital electrode of antijamming capability are provided.
The object of the present invention is achieved like this:
A kind of impedance spectrum measuring system based on wireless digital electrode, by digital electrode, single-chip microcomputer, wireless module, host computer, be connected in sequence, described digital electrode consists of electrod-array, digital switch, AD5933 and peripheral circuit thereof, what described single-chip microcomputer adopted is the ATmega16 single-chip microcomputer of Atmel company, what wireless module was selected is the NRF24L01 radio-frequency (RF) transceiver of NordicVLSI company, works in 2.4GHz-2.5GHzISM frequency range; Described host computer can be realized data analysis, curve plotting, image reconstruction according to the data that collect; First ATmega16 single-chip microcomputer passes through I
2c bus is configured AD5933, make its pumping signal that produces required frequency, then control figure switch, makes one of them electrode as exciting electrode, other electrodes are as potential electrode, and the data that finally digital electrode measured are wirelessly transmitted to host computer by wireless module.
And the structure of the peripheral circuit of described AD5933 is: the excitation end at AD5933 has increased every straight driving circuit, by 47nF electric capacity, two 50K Ω resistance, formed; Increased voltage follower circuit, what select is AD8606 two-way single power supply CMOS operational amplifier; At measuring junction, increased I-V impact damper, that select is also AD8606.
Advantage of the present invention and good effect are:
The impedance spectrum measuring system based on wireless digital electrode of the present invention's design, compare and adopted integrated form impedance measurement chip AD5933 and it has been carried out to circuit expansion with system in the past, designed digital electrode, adopt wireless transmission, there is the advantages such as simple in structure, integrated level is high, good stability, measurement range wide, be easy to carry.
Accompanying drawing explanation
Fig. 1 is the structured flowchart of AD5933 of the present invention;
Fig. 2 is digital impedance spectral measurement system block diagram of the present invention;
Fig. 3 is electrode structure schematic diagram of the present invention;
Fig. 4 is electrode operating mode circuit figure of the present invention.
Fig. 5 is AD5933 peripheral expansion circuit of the present invention.
Embodiment
Below in conjunction with accompanying drawing, describe embodiments of the invention in detail; It should be noted that, the present embodiment is narrative, is not determinate, can not limit protection scope of the present invention with this.
A kind of impedance spectrum measuring system based on wireless digital electrode, this system is comprised of digital electrode, single-chip microcomputer, wireless module, host computer, part in Fig. 2 in square frame is digital electrode block diagram, its structural drawing as shown in Figure 3, comprise that electrod-array, digital switch, AD5933 and peripheral circuit thereof form, the present embodiment by electrode and AD5933 and peripheral circuit integrated one, by digital switch, to select electrode be with AD5933 excitation end (VIN end) or measuring junction (VOUT end) is connected, thereby determine that this electrode is as exciting electrode or potential electrode.Fig. 4 is that the mode of operation of electrode is selected circuit diagram, the ADG711 chip of the ShiADI company that digital switch is selected, when K1 is closed, when K2, K3 disconnect, electrode is as exciting electrode, when K1 disconnects, when K2, K3 are closed, this electrode is as potential electrode, and K2 introduces the earth by excitation power supply, get rid of the interference of the right circuit to metrical information, in native system, adopted eight groups of these digital electrodes.
What controller adopted is the ATmega16 single-chip microcomputer of Atmel company, first ATmega16 single-chip microcomputer is configured eight AD5933 by I2C bus, make it produce the pumping signal of required frequency, then control figure change-over switch, make No. 1 electrode of electrod-array as exciting electrode, 2-8 electrode is as potential electrode, and the data that finally 2-8 digital electrode measured, by wireless module, are wirelessly transmitted to computing machine.What wireless module was selected is the NRF24L01 radio-frequency (RF) transceiver of NordicVLSI company, works in 2.4GHz-2.5GHzISM frequency range.Computing machine can be realized the functions such as data analysis, curve plotting, image reconstruction according to the data that collect.
Native system has carried out circuit expansion to AD5933, as shown in Figure 5.Excitation end (VOUT end) at AD5933 has increased every straight driving circuit, in Fig. 5,47nF electric capacity, two 50K Ω resistance form, eliminate the potential difference (PD) of AD5933 excitation end with measuring junction existence, thereby avoided tested impedance to produce the measuring error that polarization causes; In addition, also increased voltage follower circuit, as the A1 in Fig. 5, what A1 selected is AD8606 two-way single power supply CMOS operational amplifier, this circuit can be eliminated the impact of AD5933 output impedance on tested impedance, thereby from 1K Ω-10M Ω, expand the measurement range of AD5933 to 100 Ω-10M Ω, increased driving force simultaneously.At measuring junction (VIN end), increased I-V impact damper, as A2 circuit in Fig. 5, that A2 selects is also AD8606, and this circuit can be eliminated bias current, offset voltage and the CMRR impact that the inner I-V amplifier of AD5933 brings, and improves the conversion accuracy of current-voltage amplifier.
It should be noted that, although AD5933 communicates by I2C bus, but due to No. ID of AD5933 all the same, therefore 8 AD5933 can not serial carry, use same I2C bus, but with ATmega16 parallel join, and for 8 AD5933 can synchronization onwards be surveyed, in native system, 8 AD5933 are used same active crystal oscillator, as shown in Figure 2.
Principle of work of the present invention is:
The integrated form impedance measurement chip AD5933 that this measuring system has adopted AnalogDevices company to release, it integrates the unit such as DDS, ADC, DSP micro-processor kernel, can directly export the information such as the real part of impedance to be measured and imaginary part, thereby reduced the complexity of system, improved the integrated level of system; The DDS of AD5933 inside can produce specific frequency and encourage non-essential resistance, the response signal obtaining on resistance is sampled by ADC, and carry out discrete Fourier transform (DFT) by the DSP on sheet, after conversion, return to the value of real part and the imaginary values that under this output frequency, obtain, according to initial calibration data, calculate easily required resistance value, and AD5933 is by I2C bus (SCL, SDA interface) and PERCOM peripheral communication.
This measuring system has adopted eight AD5933, measure, and system in the past can only be processed a-road-through road simultaneously, thereby improve measuring speed when can realize simultaneously 7 passages (7 groups of electrodes); And native system has designed digital electrode, be about to AD5933 and be integrated on electrode, electrode is directly connected with signal measurement apparatus (AD5933 and peripheral circuit), shortened the transmission range that exchanges weak signal, eliminate external interference, avoided wave reflection phenomenon, improved the antijamming capability of system.
The digital signal of native system output adopts radio communication, be wirelessly transmitted to computing machine, for next step image reconstruction, wireless transmission has been avoided the constraint of wire cable, be easy to carry, have that integrated level is high, accuracy is high, high interference ability is strong, low in energy consumption, cost is low, wireless transmission, the advantage such as be easy to carry, have a extensive future.
Claims (2)
1. the impedance spectrum measuring system based on wireless digital electrode, it is characterized in that: by digital electrode, single-chip microcomputer, wireless module, host computer, be connected in sequence, described digital electrode consists of electrod-array, digital switch, AD5933 and peripheral circuit thereof, what described single-chip microcomputer adopted is the ATmega16 single-chip microcomputer of Atmel company, what wireless module was selected is the NRF24L01 radio-frequency (RF) transceiver of NordicVLSI company, works in 2.4GHz-2.5GHzISM frequency range; Described host computer can be realized data analysis, curve plotting, image reconstruction according to the data that collect; First ATmega16 single-chip microcomputer passes through I
2c bus is configured AD5933, make its pumping signal that produces required frequency, then control figure switch, makes one of them electrode as exciting electrode, other electrodes are as potential electrode, and the data that finally digital electrode measured are wirelessly transmitted to host computer by wireless module.
2. the impedance spectrum measuring system based on wireless digital electrode according to claim 1, it is characterized in that: the structure of the peripheral circuit of described AD5933 is: the excitation end at AD5933 has increased every straight driving circuit, by 47nF electric capacity, two 50K Ω resistance, formed; Increased voltage follower circuit, what select is AD8606 two-way single power supply CMOS operational amplifier; At measuring junction, increased I-V impact damper, that select is also AD8606.
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Cited By (2)
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| CN105675995A (en) * | 2016-02-01 | 2016-06-15 | 凯迈(洛阳)电子有限公司 | Embedded multi-channel automatic resistance measurement module |
| CN111044027A (en) * | 2020-01-02 | 2020-04-21 | 浙江大学 | Open-loop fiber optic gyroscope signal processing circuit and method using single-chip high-precision impedance transformation system |
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| CN111044027A (en) * | 2020-01-02 | 2020-04-21 | 浙江大学 | Open-loop fiber optic gyroscope signal processing circuit and method using single-chip high-precision impedance transformation system |
| CN111044027B (en) * | 2020-01-02 | 2021-09-17 | 浙江大学 | Method for demodulating signal by using open-loop optical fiber gyroscope signal processing circuit |
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Application publication date: 20140402 |