CN106419861A - Device and method for measuring photo plethysmo graphy by modulation of orthogonal square waves with lifted electrical level - Google Patents
Device and method for measuring photo plethysmo graphy by modulation of orthogonal square waves with lifted electrical level Download PDFInfo
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Abstract
The invention discloses a device and method for measuring photo plethysmo graphy by modulation of orthogonal square waves with a lifted electrical level. A microprocessor outputs lifted orthogonal square waves with different frequency, the orthogonal square waves drive at least two light emitting diodes, light emitted by the light emitting diode is received by a photosensitive device after passing through the measured finger and transformed into a voltage signal by the photosensitive device, the voltage signal is transformed into a preset amplitude voltage signal by passing through a current/voltage switching amplifier, an analog-digital converter transforms the preset amplitude voltage signal into a digital signal, the microprocessor conducts treatment on the digital signal, the photo plethysmo graphy and a valley value and a peak value of the photo plethysmo graphy are obtained, and a spectrum value is obtained through the valley value and the peak value. The measuring method comprises the steps that the microprocessor conducts separation treatment on the digital signal to obtain the photo plethysmo graphy and removes interference of background light; the valley value and the peak value are obtained according to the photo plethysmo graphy; calculation are conducted on the valley value and the peak value to obtain a absorbance difference value, and the spectrum value is obtained through the absorbance difference value. The device and method for measuring the photo plethysmo graphy by the modulation of the orthogonal square waves with the lifted electrical level to modulate the photo plethysmo graphy is precise in measurement and simple in circuit.
Description
Technical Field
The invention relates to the field of measurement of photoplethysmography, in particular to a device and a method for measuring photoplethysmography by modulating orthogonal square waves for raising a level.
Background
Photoplethysmography (Photo pulse waveform, hereinafter referred to as PPG) is an important physiological signal, and is widely used in analysis of cardiovascular system and blood components. For example, the measurement of the blood oxygen saturation is realized by measuring the PPG by using 2 or more than 2 LEDs (light emitting diodes). The PPG acquisition and the interference of the background light are usually done in a time-division manner in these measurements.
In order to improve the measurement accuracy, the prior patent application with publication number CN 102258366a and publication date 2011, 11 and 30 utilizes orthogonal square waves as excitation signals to improve the quality of signal measurement.
Since existing measurement devices employ analog-to-digital converters without exception, the analog-to-digital converters exhibit significant non-linearity near the input limit (maximum or minimum amplitude), particularly the lower the analog signal level input to the analog-to-digital converter, the greater the uncertainty in the resulting digital conversion.
Therefore, when a pure orthogonal square wave is used as an excitation signal, the signal-to-noise ratio of a digital signal obtained at a low-level part of the orthogonal square wave is very low, thereby affecting the measurement accuracy of the signal.
Disclosure of Invention
In order to improve the defects in the prior art, the technical problem to be solved by the present invention is to provide a device and a method for measuring a level-raised orthogonal square wave modulated photoplethysmographic pulse wave, wherein the device and the method can realize high-precision measurement, and have the advantages of simple circuit structure, low requirements on devices and processes, easy debugging, high reliability, small calculation amount, etc., as described in detail below:
an elevated-level quadrature square wave modulated photoplethysmography device, said photoplethysmography device comprising: a microprocessor, at least 2 light emitting diodes, a photosensitive device, a current/voltage conversion amplifier and an analog-to-digital converter,
the microprocessor outputs orthogonal square waves with different frequencies and raised levels, the orthogonal square waves with the raised levels drive at least 2 light-emitting diodes, light emitted by the light-emitting diodes is received by the photosensitive device after passing through a finger to be detected, the photosensitive device converts the light into a voltage signal, and the voltage signal is converted into a preset amplitude voltage signal by the current/voltage conversion amplifier;
the analog-to-digital converter converts the preset amplitude voltage signal into a digital signal, the microprocessor processes the digital signal to obtain a photoplethysmography and a valley value and a peak value thereof, and a spectrum value is obtained through the valley value and the peak value;
in the process of acquiring photoelectric signals by the photosensitive device, the noise level is not changed, but the orthogonal square wave signals used as the drive are obviously improved compared with noise at the low level part of the orthogonal square wave signals due to the fact that the preset level is raised, so that the signal-to-noise ratio of the photoelectric signals acquired by the photosensitive device at the low level part of the orthogonal square wave signals is improved, and the precision of digital signals input into a computer is improved.
The orthogonal square wave signal used as the drive raises the preset level, so that the signal-to-noise ratio of the photoelectric signal acquired by the photosensitive device is improved at the high-level part of the orthogonal square wave signal.
The value of the preset level is more than half of the optimal dynamic range of the photoelectric signal acquired by the photosensitive device.
The microprocessor adopts any one of MCU, ARM, DSP or FPGA.
A method of measuring an elevated level quadrature square wave modulated photoplethysmography device, the method comprising the steps of:
(1) the microprocessor adopts orthogonal square waves with different frequencies and raised levels to drive at least 2 light-emitting diodes;
(2) light emitted by the light emitting diode is received and converted into a voltage signal by the photosensitive device after passing through the detected finger, and the voltage signal is amplified into a voltage signal with a preset amplitude by the current/voltage conversion amplifier;
(3) the preset amplitude voltage signal is converted into a digital signal through an analog-to-digital converter and is sent to the microprocessor;
(4) the microprocessor separates and processes the digital signals to obtain photoplethysmography and eliminates the interference of background light;
(5) acquiring a valley value and a peak value according to the photoplethysmographic pulse wave;
(6) and calculating the valley value and the peak value to obtain an absorbance difference value, and acquiring a spectrum value through the absorbance difference value.
The invention provides a lifting orthogonal square wave modulation photoelectric volume pulse wave measuring device, which comprises: a microprocessor, at least 2 light emitting diodes, a photosensitive device, a current/voltage conversion amplifier and an analog-to-digital converter,
the microprocessor outputs raised orthogonal square waves with different frequencies, the raised orthogonal square waves drive at least 2 light emitting diodes, light emitted by the light emitting diodes is received by the photosensitive device after passing through a finger to be detected, the photosensitive device converts the light into a voltage signal, the voltage signal is converted into a preset amplitude voltage signal through the current/voltage conversion amplifier, the analog-to-digital converter converts the preset amplitude voltage signal into a digital signal, the microprocessor processes the digital signal to obtain a photoplethysmography wave and a valley value and a peak value thereof, and a spectrum value is obtained through the valley value and the peak value.
The microprocessor adopts any one of MCU, ARM, DSP or FPGA.
The invention provides a method for measuring a raised orthogonal square wave modulated photoplethysmogram, which comprises the following steps:
(1) the microprocessor drives at least 2 light-emitting diodes by adopting lifting orthogonal square waves with different frequencies;
(2) light emitted by the light emitting diode is received and converted into a voltage signal by the photosensitive device after passing through the detected finger, and the voltage signal is amplified into a voltage signal with a preset amplitude by the current/voltage conversion amplifier;
(3) the preset amplitude voltage signal is converted into a digital signal through an analog-to-digital converter and is sent to the microprocessor;
(4) the microprocessor separates and processes the digital signals to obtain photoplethysmography and eliminates the interference of background light;
(5) acquiring a valley value and a peak value according to the photoplethysmographic pulse wave;
(6) and calculating the valley value and the peak value to obtain an absorbance difference value, and acquiring a spectrum value through the absorbance difference value.
Compared with the prior art, the orthogonal square wave modulation photoplethysmography measuring device and method for raising the level provided by the invention have the following advantages: according to the Lambert-beer law, orthogonal square wave frequency division modulation and digital demodulation technologies are adopted, compared with the patent application with the publication number of CN 102258366A in the background technology and the publication date of 2011, 11 and 30, the orthogonal square waves for raising the preset level are adopted to drive at least 2 light-emitting diodes, light emitted by the light-emitting diodes is received by a photosensitive device after passing through a detected finger, and then is converted into preset amplitude voltage signals through a current/voltage conversion amplifier, and the preset amplitude voltage signals are converted into digital signals through an analog-to-digital converter; and the microprocessor processes the digital signal to obtain a spectral value. The invention obviously improves the signal-to-noise ratio of the photoelectric signal in the low-level section of the orthogonal square wave signal and improves the preset amplitude voltage signal, thereby improving the precision of signal acquisition and meeting various requirements in practical application.
Drawings
FIG. 1 is a schematic diagram of the principle of calculating absorbance provided by the present invention;
FIG. 2 is a schematic structural diagram of an orthogonal square wave modulated photoplethysmography device with elevated level according to the present invention;
FIG. 3 is a schematic diagram of an elevated level quadrature square wave provided by the present invention;
FIG. 4 is a flow chart of a method for measuring a photoplethysmogram with orthogonal square wave modulation for raising the level according to the present invention;
fig. 5 is another schematic structural diagram of the level-raised quadrature square wave modulated photoplethysmography apparatus according to the present invention.
The list of components represented by the various reference numbers in the figures is as follows:
1: a microprocessor; 2: a light emitting diode;
3: a photosensitive device; 4: a current/voltage conversion amplifier;
5: an analog-to-digital converter; PX.1: an I/O port;
PX.2: an I/O port; PX.n: an I/O port;
PX.3: an I/O port; PX.4: an I/O port;
r1: a first resistor; VCC: a power source;
r2: a second resistor; r3: a third resistor;
r4: a fourth resistor; r5: a fifth resistor;
r6: a sixth resistor; c1: a first capacitor;
c2: a second capacitor; d1: a first light emitting diode;
d2: a second light emitting diode; d3: a third light emitting diode;
d4: a fourth light emitting diode; a1: an operational amplifier;
PY port: and an I/O port.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
Example 1
The blood flow in the blood vessel changes periodically due to the pulsation of the artery, and since blood is a highly opaque liquid, the change in pulse inevitably causes a change in absorbance, as shown in fig. 1.
Considering the state of minimum arterial blood vessel filling degree, the incident light from the light source is not absorbed by the pulsating arterial blood, and the emergent light intensity I ismaxStrongest, incident light I, which can be regarded as pulsatile arterial blood; the state of the highest filling degree of the arterial blood vessels corresponds to the valley point of the photoelectric pulse wave, namely the moment of the maximum action of the pulsating arterial blood, and the emergent light intensity I at the momentminThe weakest is the minimum emergent light intensity I of the pulsating arterial blood. Therefore, the influence of all human body components with constant absorption characteristics, such as skin tissues, subcutaneous tissues and the like, on the absorbance can be eliminated by recording the absorbance values when the artery is filled to the maximum and when the artery is contracted to the minimum.
According to the modified Lambert-beer law, let I0I is the incident and emergent intensities, respectively, α is the molecular extinction coefficient, c is the concentration of each component, l is the average optical path length of light in the tissue, G is the light loss due to scattering, the absorbance a can be expressed as:
let the absorption coefficient of the biological tissue be muaThen μaα c, the formula (1) can be substituted by:
A＝-2.303μal+G (2)
in light transmission detection, absorbance is primarily composed of absorption and scattering by the transmitted tissue, with blood scattering being relatively small and negligible. Thus, G is contributed only by tissues other than the pulsating arterial blood, and remains unchanged during the measurement. Let n layers of the tissue to be transmitted except for the pulsating arterial blood, and the absorption coefficient of the i-th layer be mutiAbsorption coefficient of arterial blood of μabThe maximum optical path length is l when the artery is full in a photoelectric pulse wave periodmaxThe minimum optical path length at the time of arterial contraction is lminWhen the artery is full, the absorbance A1And absorbance A at the time of arterial contraction2Can be respectively expressed as:
let l bemaxAnd lminThe difference between them. Since the tissue other than the pulsating arterial blood is substantially stable and does not undergo periodic changes, this portion has no effect on the absorbance during filling and contraction of the artery, i.e. the first component in equations (3) and (4) is equal. The difference between the absorbance at arterial filling and the absorbance at arterial constriction is:
ΔA＝A1-A2＝-2.303μab(lmax-lmin)＝-2.303μabl (5)
in the above derivation, the absorption and scattering components of the non-pulsating blood and the tissue layers are eliminated, and the difference Δ a between the absorption when the artery is full and the absorption when the artery is contracted is only partially contributed by the pulsation absorption of the arterial blood, mainly reflecting the absorption change of the pulsating arterial blood. The effects essentially corresponding to those of the tissue to be transmitted, the skin, the muscle, the venous blood and other tissues except the pulsating arterial blood, are removed, leaving only the pure pulsating arterial blood portion for the measurement of the absorbance difference Δ a. In this way, the effects of individual differences in skin, bone and muscle are removed.
Let the incident light intensity be I0The detected light intensity when the artery is full and the detected light intensity when the artery is contracted are I respectivelyminAnd ImaxAnd the difference value delta A between the absorbance when the artery is full and the absorbance when the artery is contracted is as follows:
measuring the valley I of each photoplethysmogramminAnd peak value ImaxThe absorbance difference Delta A corresponding to the photoplethysmogram can be obtainedλ1、ΔAλ2……ΔAλnSpectral values of the composition.
An elevated level quadrature square wave modulated photoplethysmography apparatus, see fig. 2, comprising: microprocessor 1, at least 2 kinds of light-emitting diodes 2, photosensitive device 3, current/voltage conversion amplifier 4 and analog-to-digital converter 5.
The microprocessor 1 outputs orthogonal square waves with different frequencies and elevated levels, the orthogonal square waves with the elevated levels drive at least 2 light emitting diodes 2, light emitted by the light emitting diodes 2 is received by the photosensitive device 3 after passing through a finger to be detected, the photosensitive device 3 converts the light into a voltage signal, and the voltage signal is converted into a preset amplitude voltage signal through the current/voltage conversion amplifier 4.
After the preset level is raised, the noise level is not changed in the process of acquiring the photoelectric signal by the photosensitive device 3, but the orthogonal square wave signal used as the drive is obviously improved compared with the noise at the low level part of the orthogonal square wave signal because the preset level is raised, so that the signal-to-noise ratio of the photoelectric signal at the low level section of the orthogonal square wave signal is improved; compared with the patent application with publication number CN 102258366a and publication date 2011, 11 and 30, in which a pure orthogonal square wave is used as an excitation signal, in the background art, the embodiment of the invention significantly improves the signal-to-noise ratio of the photoelectric signal in the low-level section of the orthogonal square wave signal, thereby improving the quality of the photoelectric signal acquired by the photosensitive device 3.
In addition, the noise level is not changed due to the fact that the preset level is raised, the orthogonal square wave signal is improved to a certain extent compared with noise in the high-level part of the orthogonal square wave signal, and the signal-to-noise ratio of the photoelectric signal in the high-level section of the orthogonal square wave signal is improved.
Furthermore, the signal-to-noise ratio of the photoelectric signal acquired by the photosensor 3 is integrally enhanced, so that the precision of the digital signal input into the microprocessor 1 is improved, and the microprocessor 1 processes the digital signal to obtain a spectral value.
When the value of the preset level is preferably more than half of the dynamic range of the photoelectric signal collected by the photosensitive device 3, and when the value is greater than or equal to 1/2 dynamic range, the quality of the photoelectric signal collected by the photosensitive device 3 is the highest.
The analog-to-digital converter 5 converts the preset amplitude voltage signal into a digital signal, the microprocessor 1 processes the digital signal to obtain a photoplethysmography, a valley value and a peak value thereof, and a spectrum value is obtained through the valley value and the peak value.
Wherein, the number of the light emitting diodes 2 is more than or equal to 2. In a specific implementation, the number of the light emitting diodes 2 is set according to a requirement in an actual application, which is not limited in the embodiment of the present invention.
The preset amplitude is set according to the needs of practical application, and in the specific implementation, the embodiment of the present invention does not limit this.
The microprocessor 1 may be any one of MCU, ARM, DSP or FPGA.
In summary, compared with the application documents in the background art, the embodiment of the present invention significantly improves the signal-to-noise ratio of the photoelectric signal in the low level section of the orthogonal square wave, and also improves the signal-to-noise ratio of the photoelectric signal in the high level section of the orthogonal square wave, thereby improving the signal-to-noise ratio of the photoelectric signal in the whole level section, improving the accuracy of the digital signal input into the microprocessor, and the microprocessor processes the digital signal to obtain the spectrum value.
Example 2
An elevated level quadrature square wave modulated photoplethysmography method, see fig. 3 and 4, comprising the steps of:
101: the microprocessor 1 adopts orthogonal square waves with different frequencies and raised levels to drive at least 2 light-emitting diodes 2;
102: light emitted by the light emitting diode 2 passes through a finger to be detected, is received by the photosensitive device 3 and is converted into a voltage signal, and the voltage signal is amplified into a voltage signal with a preset amplitude value through the current/voltage conversion amplifier 4;
103: the preset amplitude voltage signal is converted into a digital signal by an analog-to-digital converter 5 and sent to the microprocessor 1;
104: the microprocessor 1 separates and processes the digital signals to obtain photoelectric volume pulse waves and eliminates the interference of background light;
105: acquiring a valley value and a peak value according to the photoplethysmography;
for the sake of simplicity, the light emitting diodes 2 with 4 wavelengths are taken as an example for explanation, assuming that the light emitting diodes 2 with λ 1(D1 light emitting diode) and λ 2(D2 light emitting diode) wavelengths drive the orthogonal square wave frequency by 2 times f, the light emitting diodes 2 with λ 3(D3 light emitting diode) and λ 4(D4 light emitting diode) wavelengths drive the orthogonal square wave frequency by 1 times f, and the driving orthogonal square wave frequencies of the light emitting diodes 2 with λ 1 and λ 2 wavelengths are the same but are 90 ° out of phase, and the driving orthogonal square wave frequencies of the light emitting diodes 2 with λ 3 and λ 4 wavelengths are the same but 90 ° out of phase.
Assume that the sampling frequency of the analog-to-digital converter 5 is fS, and fS is 2f, and it is guaranteed to sample in the middle of the high and low levels of the λ 1 drive signal.
Digital signal sequenceCan be expressed as:
wherein,andphotoplethysmographic waves of wavelengths λ 1, λ 2, λ 3 and λ 4 respectively,is the sum signal of the background light and the dark current of the photosensitive device 3 and the offset voltage of the current/voltage conversion amplifier 4 (referred to as background signal for short, including the effect of the raised level part of each wavelength).
Assuming that the sampling frequency fS is much higher than the variation frequency of the modulated orthogonal square wave signal and the background light, the amplitude of each path of orthogonal square wave signal and the amplitude of the background light signal can be approximately considered to be unchanged in one period of the lowest driving signal frequency. Take the first 8 samples as an example:
wherein,andthe amplitudes of the optical and background signals (including the contribution of the elevated level portions of the respective wavelengths) at wavelengths λ 1, λ 2, λ 3 and λ 4, respectively.
In other words, the operation is performed in order every 8 digital signals:
that is, 4 times of photoplethysmography with wavelength λ 1 is obtainedAnd completely eliminates background signals (including the effect of elevated level portions for each wavelength)The influence of (c).
Namely, 4 times of photoplethysmography with wavelength lambda 2 is obtainedAnd completely eliminates background signals (including the effect of elevated level portions for each wavelength)The influence of (c).
Namely, 4 times of the photoplethysmography with the wavelength lambda 3 is obtainedAnd completely eliminates background signals (including the effect of elevated level portions for each wavelength)The influence of (c).
Namely, 4 times of the photoplethysmography with the wavelength lambda 4And completely eliminates background signals (including the effect of elevated level portions for each wavelength)The influence of (c).
The photoplethysmography valley and peak values at wavelengths λ 1, λ 2, λ 3, and λ 4 are calculated, respectively: i isminλ1、Imaxλ1、Iminλ2、Imaxλ2、Iminλ3、Imaxλ3、Iminλ4And Imaxλ4；
106: and calculating the valley value and the peak value to obtain an absorbance difference value, and acquiring a spectrum value through the absorbance difference value.
The difference Δ A in absorbance was calculated by the following equation (6)λ1、ΔAλ2、……ΔAλnAnd the difference in absorbance constitutes the spectral value.
In summary, compared with the application documents in the background art, the embodiments of the present invention significantly improve the signal-to-noise ratio of the photoelectric signal in the low level section of the triangular wave, and also improve the signal-to-noise ratio of the photoelectric signal in the high level section of the triangular wave, thereby improving the signal-to-noise ratio of the photoelectric signal in the whole level section, improving the accuracy of the digital signal input to the microprocessor, and the microprocessor processes the digital signal to obtain the spectrum value.
Example 3
As shown in fig. 5, a quadrature square wave modulated photoplethysmography measuring apparatus with elevated level employs 4 light emitting diodes 2, four I/O ports px.1, px.2, px.3 and px.4 of a microprocessor 1 respectively drive a first light emitting diode D1, a second light emitting diode D2, a third light emitting diode D3 and a fourth light emitting diode D4 through a first resistor R1, a second resistor R2, a third resistor R3 and a fourth resistor R4, light transmitted by the first light emitting diode D1, the second light emitting diode D2, the third light emitting diode D3 and the fourth light emitting diode D4 is received by a photosensor 3, signals received by the photosensor 3 are converted into preset amplitude/voltage signals through a current/voltage conversion amplifier 4 composed of an operational amplifier a1, a first capacitor C1, a second capacitor C2, a fifth resistor R5 and a sixth resistor R6, the adc 5 then converts the preset amplitude voltage signal into a digital signal at a speed twice the frequency of the highest driving led 2, and sends the digital signal to the microprocessor 1 through the PY port. The digital signal is firstly separated into the pulse wave signals with different wavelength photoplethysmography at the microprocessor 1: each sequentially acquired 8 digital signals are grouped according to
That is, 4 times of the photoplethysmographic pulse waves with wavelengths of λ 1, λ 2, λ 3 and λ 4 are obtainedAndand completely eliminates background signals (including the effect of elevated level portions for each wavelength)The influence of (c).
Obtaining the photoplethysmography of each wavelength, and calculating the valley value and peak value of the photoplethysmography of lambda 1, lambda 2, lambda 3 and lambda 4 according to the photoplethysmography: i isminλ1、Imaxλ1、Iminλ2、Imaxλ2、Iminλ3、Imaxλ3、Iminλ4And Imaxλ4。
Then is composed ofminλ1、Imaxλ1、Iminλ2、Imaxλ2、Iminλ3、Imaxλ3、Iminλ4And Imaxλ4Calculating the absorbance difference Delta A corresponding to each wavelength to obtain the absorbance difference Delta Aλ1、ΔAλ2……ΔAλnSpectral values of the composition.
In summary, compared with the application documents in the background art, the embodiment of the present invention significantly improves the signal-to-noise ratio of the photoelectric signal in the low level section of the orthogonal square wave, and also improves the signal-to-noise ratio of the photoelectric signal in the high level section of the orthogonal square wave, thereby improving the signal-to-noise ratio of the photoelectric signal in the whole level section, improving the accuracy of the digital signal input into the microprocessor, and the microprocessor processes the digital signal to obtain the spectrum value.
Those skilled in the art will appreciate that the drawings are only schematic illustrations of preferred embodiments, and the above-described embodiments of the present invention are merely provided for description and do not represent the merits of the embodiments.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (5)
1. An elevated level quadrature square wave modulated photoplethysmography device, comprising: a microprocessor, at least 2 light emitting diodes, a photosensitive device, a current/voltage conversion amplifier and an analog-to-digital converter,
the microprocessor outputs orthogonal square waves with different frequencies and raised levels, the orthogonal square waves with the raised levels drive at least 2 light-emitting diodes, light emitted by the light-emitting diodes is received by the photosensitive device after passing through a finger to be detected, the photosensitive device converts the light into a voltage signal, and the voltage signal is converted into a preset amplitude voltage signal by the current/voltage conversion amplifier;
the analog-to-digital converter converts the preset amplitude voltage signal into a digital signal, the microprocessor processes the digital signal to obtain a photoplethysmography and a valley value and a peak value thereof, and a spectrum value is obtained through the valley value and the peak value;
in the process of acquiring photoelectric signals by the photosensitive device, the noise level is not changed, but the orthogonal square wave signals used as the drive are obviously improved compared with noise at the low level part of the orthogonal square wave signals due to the fact that the preset level is raised, so that the signal-to-noise ratio of the photoelectric signals acquired by the photosensitive device at the low level part of the orthogonal square wave signals is improved, and the precision of digital signals input into a computer is improved.
2. The apparatus according to claim 1, wherein the driving quadrature square wave signal raises the predetermined level, so that the signal-to-noise ratio of the photo-sensor to the photo-electric signal is increased at the high level of the quadrature square wave signal.
3. The apparatus according to claim 1, wherein the preset level is preferably set to a value more than half of the dynamic range of the photoelectric signal collected by the photosensor.
4. The apparatus of claim 1, wherein the microprocessor is any one of MCU, ARM, DSP or FPGA.
5. A measurement method for an elevated level quadrature square wave modulated photoplethysmography apparatus according to claims 1 to 4, characterized in that said method comprises the steps of:
(1) the microprocessor adopts orthogonal square waves with different frequencies and raised levels to drive at least 2 light-emitting diodes;
(2) light emitted by the light emitting diode is received and converted into a voltage signal by the photosensitive device after passing through the detected finger, and the voltage signal is amplified into a voltage signal with a preset amplitude by the current/voltage conversion amplifier;
(3) the preset amplitude voltage signal is converted into a digital signal through an analog-to-digital converter and is sent to the microprocessor;
(4) the microprocessor separates and processes the digital signals to obtain photoplethysmography and eliminates the interference of background light;
(5) acquiring a valley value and a peak value according to the photoplethysmographic pulse wave;
(6) and calculating the valley value and the peak value to obtain an absorbance difference value, and acquiring a spectrum value through the absorbance difference value.
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| CN107167441A (en) * | 2017-07-02 | 2017-09-15 | 广东技术师范学院 | The method that double light path and multiposition modulated light sources measure complicated solution component content |
| CN107179284A (en) * | 2017-07-02 | 2017-09-19 | 广东技术师范学院 | The method of double packed complicated solution component contents of optical path modulation light source measurement |
| CN107290317A (en) * | 2017-07-02 | 2017-10-24 | 广东技术师范学院 | The method that double optical path modulation fluorescence excitation light sources measure packed complicated solution composition |
| CN107290291A (en) * | 2017-07-02 | 2017-10-24 | 广东技术师范学院 | The method that double optical path modulation transmissions and fluorescence excitation light source measure complicated solution composition |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107167441A (en) * | 2017-07-02 | 2017-09-15 | 广东技术师范学院 | The method that double light path and multiposition modulated light sources measure complicated solution component content |
| CN107179284A (en) * | 2017-07-02 | 2017-09-19 | 广东技术师范学院 | The method of double packed complicated solution component contents of optical path modulation light source measurement |
| CN107290317A (en) * | 2017-07-02 | 2017-10-24 | 广东技术师范学院 | The method that double optical path modulation fluorescence excitation light sources measure packed complicated solution composition |
| CN107290291A (en) * | 2017-07-02 | 2017-10-24 | 广东技术师范学院 | The method that double optical path modulation transmissions and fluorescence excitation light source measure complicated solution composition |
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