CN115299909A - PPG waveform and heart rate detection system realized by hardware - Google Patents
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Abstract
The invention discloses a PPG waveform and heart rate detection system realized by hardware, which comprises: the infrared photoelectric sensor is used for detecting the pulse waveform of the fingertip of a human body to obtain a pulse signal; the analog-to-digital converter is used for performing analog-to-digital conversion on the pulse signal to obtain a pulse wave signal; the pulse wave signal processing module comprises a heart rate hardware counting unit and a heart rate waveform pixel hardware processing unit, wherein the heart rate hardware counting unit is used for calculating a heart rate value according to a pulse wave signal and controlling a display screen to display the heart rate value; the heart rate waveform pixel hardware processing unit is used for controlling the display screen to display the PPG waveform according to the pulse wave signal; and the display screen is used for displaying the PPG waveform and the heart rate value. Compared with the existing software for processing the pulse wave signals, the invention uses hardware for processing to ensure that the overall power consumption of the system is lower, the speed is higher and the area is smaller, thereby having more market competitiveness. The invention can be widely applied to the technical field of medical equipment and human body signal detection.
Description
Technical Field
The invention relates to the technical field of medical equipment and human body signal detection, in particular to a PPG waveform and heart rate detection system realized by hardware.
Background
During the heart beating cycle, the blood volume shows pulsatile changes along with the contraction and relaxation of the heart, and the changes are obtained by the principle of photoelectric conversion, which is called photoplethysmography (PPG) signals. The PPG signal is an important human body physiological signal, contains a large amount of physiological information reflecting human body conditions, and can realize detection of a plurality of physiological parameters through analysis and calculation. PPG can also be applied to the research of evaluating the state of cardiovascular, respiratory and blood circulation systems of human bodies, evaluating the automatic regulation capability of the brain in a non-contact way, detecting the alcohol concentration in a non-invasive way, recognizing emotion, psychophysiology and the like. By analyzing and calculating the PPG signal, the physiological parameters such as pulse rate, blood oxygen saturation, blood pressure, microcirculation and the like can be directly or indirectly calculated, and the characteristic quantity in the signal can be extracted to further realize the detection of related diseases.
Most instruments for detecting pulse waves and heart rates in the market at present use software to perform signal processing, and in the software processing, data needs to be operated, so that high requirements are imposed on hardware equipment, and the hardware equipment is large and high in energy consumption. In addition, most heart rate detection instruments in the market do not support waveform display, or the heart rate waveform is seriously distorted, and the waveform details are not easy to analyze.
Disclosure of Invention
To solve at least one of the technical problems in the prior art to a certain extent, an object of the present invention is to provide a PPG waveform and heart rate detection system implemented by hardware.
The technical scheme adopted by the invention is as follows:
a PPG waveform and heart rate detection system implemented in hardware, comprising:
the infrared photoelectric sensor is used for detecting the pulse waveform of the fingertip of a human body to obtain a pulse signal;
the analog-to-digital converter is used for performing analog-to-digital conversion on the pulse signal to obtain a pulse wave signal;
the pulse wave signal processing module comprises a heart rate hardware counting unit and a heart rate waveform pixel hardware processing unit, wherein the heart rate hardware counting unit is used for calculating a heart rate value according to a pulse wave signal and controlling a display screen to display the heart rate value; the heart rate waveform pixel hardware processing unit is used for controlling the display screen to display the PPG waveform according to the pulse wave signal;
and the display screen is used for displaying the PPG waveform and the heart rate value.
Furthermore, a filter circuit which is composed of three levels of high-pass, low-pass and high-pass structures is arranged on the infrared photoelectric sensor, and the filter circuit is used for filtering the pulse signals.
Further, the light emitting device on the infrared photoelectric sensor is powered by a pulse sequence with a preset frequency.
Further, the heart rate hardware counting unit calculates the number of pulses by detecting the rising edge of one pulse period, and calculates the heart rate value according to the number of pulses.
Further, the heart rate hardware counting unit comprises three registers, namely a first register, a second register and a third register;
the counting process is as follows:
determining a value a, wherein the value a is between the peak value and the peak value of the pulse wave signal;
comparing the acquired pulse signal values with a value a one by one, and setting a first register to be 1 when the pulse signal value is more than or equal to a; when the pulse signal value is less than a, setting the first register to be 0;
adding 1 to the numerical value of the second register every time the first register jumps from 0 to 1, and resetting the count value of the second register to 0 when the count value of the second register reaches n;
when the numerical value of the second register is detected to be 0, setting the third register to be 0, and when the numerical value of the second register is detected not to be 0, enabling the third register to count the input clock;
acquiring a time value T of the second register from the value 1 to the value n:
in the formula, CLK is the input clock frequency, c is the counting result of the third register;
and calculating to obtain a heart rate value according to the obtained time value.
Further, the heart rate hardware counting unit controls a display screen to display the heart rate value by the following method:
acquiring a unit display area, a ten-digit display area and a hundred-digit display area on a display screen;
for each display area, coordinate pixels corresponding to ten numbers, namely 0 to 9, are stored in advance;
and after the heart rate value is obtained through calculation, controlling the corresponding coordinate pixel to display according to the heart rate value.
Further, the heart rate waveform pixel hardware processing unit controls the display screen to display the PPG waveform by:
interacting with a display screen through the FPGA;
and selecting a display area for displaying the PPG waveform in the display screen, mapping the pulse wave signal and the coordinate value of the display area, and obtaining and controlling the corresponding pixel point to display so as to display the PPG waveform in the display screen.
Further, the pulse wave signal processing module is also used for separating the pulse wave signal during AD sampling so as to separate a direct current component of the PPG from direct current noise of the power supply.
Furthermore, when the infrared photoelectric sensor needs to detect pulse wave signals corresponding to a plurality of light waves with different wavelengths at the same time, different pulse wave signals are separated in the AD sampling process, and therefore the fact that one path of detector channel receives multiple paths of input waveforms at the same time is achieved.
Further, the display screen is an electronic ink screen.
The invention has the beneficial effects that: compared with the existing software for processing the pulse wave signals, the invention uses hardware for processing to ensure that the overall power consumption of the system is lower, the speed is higher and the area is smaller, thereby having more market competitiveness.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following description is made on the drawings of the embodiments of the present invention or the related technical solutions in the prior art, and it should be understood that the drawings in the following description are only for convenience and clarity of describing some embodiments in the technical solutions of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.
Fig. 1 is a block diagram of a PPG waveform and heart rate detection system implemented by hardware in an embodiment of the present invention;
FIG. 2 is a schematic diagram of the operation of an infrared photosensor in an embodiment of the present invention;
FIG. 3 is a block diagram of a signal processing flow of an infrared photoelectric sensor in an embodiment of the present invention;
FIG. 4 is a block diagram of the signal processing flow of the pulse wave signal processing module according to the embodiment of the present invention;
FIG. 5 is a schematic diagram of a waveform and pulse rate of a display screen according to an embodiment of the present invention;
FIG. 6 is a simulated waveform diagram of receiving dual wavelengths in an embodiment of the present invention;
fig. 7 is a measured waveform diagram of a received single wavelength in an embodiment of the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention and are not to be construed as limiting the present invention. The step numbers in the following embodiments are provided only for convenience of illustration, the order between the steps is not limited at all, and the execution order of each step in the embodiments can be adapted according to the understanding of those skilled in the art.
In the description of the present invention, it should be understood that the orientation or positional relationship referred to in the description of the orientation, such as the upper, lower, front, rear, left, right, etc., is based on the orientation or positional relationship shown in the drawings, and is only for convenience of description and simplification of description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention.
In the description of the present invention, the meaning of a plurality of means is one or more, the meaning of a plurality of means is two or more, and larger, smaller, larger, etc. are understood as excluding the number, and larger, smaller, inner, etc. are understood as including the number. If the first and second are described for the purpose of distinguishing technical features, they are not to be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated or implicitly indicating the precedence of the technical features indicated.
In the description of the present invention, unless otherwise explicitly limited, terms such as arrangement, installation, connection and the like should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above terms in the present invention in combination with the specific contents of the technical solutions.
As shown in fig. 1, this embodiment provides a PPG waveform and heart rate detection system implemented by hardware, which includes:
the infrared photoelectric sensor is used for detecting the pulse waveform of the fingertip of a human body to obtain a pulse signal;
the analog-to-digital converter is used for performing analog-to-digital conversion on the pulse signals to obtain pulse wave signals;
the pulse wave signal processing module comprises a heart rate hardware counting unit and a heart rate waveform pixel hardware processing unit, wherein the heart rate hardware counting unit is used for calculating a heart rate value according to a pulse wave signal and controlling a display screen to display the heart rate value; the heart rate waveform pixel hardware processing unit is used for controlling the display screen to display the PPG waveform according to the pulse wave signal;
and the display screen is used for displaying the PPG waveform and the heart rate value.
The pulsation of the human fingertip is detected by means of infrared photosensors, see fig. 2, either using projected light as output signal, as shown in fig. 2 (a), or reflected light as output signal, as shown in fig. 2 (b). The output signal changes according to the change of the received light intensity, and the blood volume of the artery changes in the pulse fluctuation process, so that the absorption of infrared light changes, the output signal of the sensor changes, and the waveform of the pulse pulsation process can be detected according to the principle.
Referring to fig. 3, as an alternative embodiment, a filter circuit composed of three stages in a high-pass-low-pass-high-pass configuration is disposed on the infrared photoelectric sensor, and the filter circuit is used for filtering the pulsating signal, and the filtered signal enters an amplifier for amplification. The direct current lifting can be effectively reduced, and the magnification factor can be increased; in particular, the waveform details are preserved to avoid the waveform being compressed as it passes through the amplifier due to dc-boost.
As an alternative embodiment, the light emitting device on the infrared photosensor is powered by a pulse train of a preset frequency. In particular, the pulse waveform may be a square wave. The method comprises the following steps of supplying power to a light-emitting device by using square waves, namely generating a light source flashing at a certain frequency, and modulating PPG alternating current and direct current to high frequency at the same time before PPG is received to keep the value of signal alternating current and direct current; in addition, because the operation is realized by pure hardware, the sampling time can be accurately controlled, so that the operation can be realized in a low-performance system; therefore, the influence of the power supply direct current on the signal direct current doping can be avoided. This method can also suppress ambient noise since the final calculation is to use the value of the lamp-on signal minus the value of the lamp-off signal.
When the PPG is used for detecting complex parameters, some parameters such as the blood oxygen saturation require extraction of direct current components of the PPG, or require simultaneous detection of PPG signals corresponding to a plurality of different wavelengths.
As a further optional implementation, the power supply of the light emitting device is also chopped, and the obtained pulse sequence is input into the light emitting device, which is equivalent to that the PPG dc + ac signal is modulated to a higher frequency before the signal is input, so that the dc component in the PPG is distinguished from the dc component of the power supply.
Referring to fig. 6 and 7, if the PPG signals corresponding to two light waves with different wavelengths need to be detected simultaneously, only one valid signal exists at any time by alternately turning on and off the light emitting devices with two different wavelengths, and at this time, only one receiving tube is needed to receive all the signals. E.g. simultaneously detecting the wavelength lambda if necessary 1 And λ 2 Then each cycle of reception should include λ 1 Lamp on, lambda 2 Turning off the lamp; lambda [ alpha ] 1 Lamp bulb、λ 2 The lamp is on; lambda [ alpha ] 1 Lamp off, lambda 2 The lamp is off for three periods of time. As long as the chopping frequency is high enough to meet the Nyquist sampling theorem, the acquired signals can be ensured to be free of distortion. The hardware implementation detection system provided by the invention is matched with a chopped pulse sequence to carry out sampling control, can accurately control the sampling time, and can separate signals corresponding to three time periods in sampling. In summary, the present embodiment uses square wave power to supply power to the light emitting device to achieve simultaneous collection of multiple wavelength signals. If two light emitting devices with different wavelengths flash alternately, only one effective PPG signal is needed at any moment, only one receiving tube is needed to receive the signal, and the signal is separated in AD sampling, so that one channel can acquire multiple signals, and the circuit area consumption is greatly reduced.
In summary, the present embodiment uses the operation of chopping the input, which has two advantages: firstly, the direct current component of the PPG can be separated from the direct current noise of a power supply, so that the accuracy of a detection result is improved; and secondly, the multi-channel input waveform can be received by using one-channel detector, and the whole area of the system is reduced. The use of hardware to implement the system in the present invention makes it possible to implement the above two points at low cost, which is not possible in a software system.
Referring to fig. 4, the filtered and amplified signal is input to an analog-to-digital converter, and after analog-to-digital conversion, a pulse wave signal is obtained and input to a pulse wave signal processing module for processing, which mainly includes heart rate counting and pulse waveform display processing.
Wherein, the pulse waveform display processing comprises: the waveform pixels are obtained by comparing the values sampled from the analog-to-digital converter with the display screen coordinates. Firstly, according to the pixel coordinate distribution of the display screen, selecting the area therein to display the waveform. And mapping the input signal value and the screen coordinate value to draw out corresponding screen pixel points, wherein all the pixel points form a waveform signal and output the waveform signal to the display screen.
Heart rate counting is achieved by:
first, for pulse wave signals, the pulse number is counted by detecting the rising edge of one pulse period, and three registers, assuming that registers 1, 2, and 3 are used for data recording, are required. It should be noted that, in the present embodiment, three registers are used for implementation, but the present invention is not limited to three registers, and a technical solution implemented by using any number of registers should fall within the protection scope of the present invention.
The specific implementation mode is as follows: determining a value a between the peak value and the peak value of the pulse wave signals input by the analog-to-digital converter, and comparing the acquired pulse signal values with the value a one by one. When the pulse signal value is larger than or equal to a, setting the register 1 to be 1, and when the pulse signal value is smaller than a, setting the register 1 to be 0; each time register 1 jumps from 0 to 1, register 2 is incremented by 1 and when the count value of register 2 reaches 6, the register 2 count value is reset to 0. When the value of the register 2 is detected to be 0, the register 3 is set to be 0, and when the value of the register 2 is detected not to be 0, the register 3 is enabled to count the input clock. Then, the precise time value of the register 2 from the value 1 to the value 6 (i.e. 5 pulse beats) can be finally obtained, and assuming that the input clock frequency is CLK and the counting result of the register 3 is c, the time T is:
according to the above operation, each time a complete cycle time of 5 pulse beats is counted (note that, here, 5 times are not necessarily recorded, and the number of recorded cycles can be adjusted according to actual needs), the heart rate can be calculated:
if the time required for recording the pulse beats n times, then the heart rate:
and after obtaining the heart rate value HR, respectively selecting corresponding pixels according to the numerical value of each bit, and sending the pixels to a display screen for display.
As an alternative embodiment, ten numbers of coordinate pixels, that is, numbers 0 to 9, are drawn in advance according to the pixel coordinates of the display screen, after the heart rate value HR is calculated, the numbers corresponding to the respective bits of HR are calculated, and the corresponding digital pixel at the corresponding position is selected to be or operated with the waveform pixel to synthesize an image of one frame, and then the synthesized pixel is sent to the display screen for display, as shown in fig. 5.
Further as an alternative embodiment, regarding the determination of the value a, a specific value may be determined here according to the coordinates of the waveform displayed on the screen. Different detected individuals can have different peak-to-peak values, but the common characteristic is that the minimum value of the waveform is a fixed value, and as long as the coordinate value of the fixed value is found and the value a is slightly larger than the value, the rising edge of the waveform can be stably detected and the influence of pulse secondary waves can be avoided.
Because counting is implemented using hardware, the speed and accuracy of obtaining heart rate values is much greater than software implementations. On the display speed, if 5 pulse beating cycles are recorded, the heart rate value can be displayed by only 5 pulse beating times; in terms of recording time accuracy, if the 200kHz clock frequency is sampled for counting, the time accuracy can reach 5us.
And after the heart rate value is obtained through calculation, sending the processed heart rate value pixels and waveform pixels to a display screen for display. As an alternative embodiment, the display screen is an electronic ink screen. It should be noted that, in addition to the electronic ink screen, other functions may be implemented.
In summary, compared with the prior art, the present embodiment has the following advantages and beneficial effects:
(1) The heart rate value is calculated by adopting hardware, so that the power consumption can be reduced, the detection speed is increased, the precision is improved, and the one-time heartbeat cycle time can be accurately obtained.
(2) A high-pass-low-pass filter is arranged on the infrared photoelectric sensor, so that the details of the waveform can be reserved, and the waveform is prevented from being compressed when passing through an amplifier due to the direct current rise.
(3) The invention uses square wave to supply power to a light-emitting device, namely a light source with a certain frequency flicker is generated, PPG alternating current and direct current are simultaneously modulated to high frequency before PPG is received, and the signal alternating current and direct current value is reserved; and because the operation is realized by pure hardware, the sampling time can be accurately controlled, so that the operation can be realized in a low-performance system; the innovation point can avoid the influence of the power supply direct current on the signal direct current doping. Since the final calculation is to use the lamp-on signal value minus the lamp-off signal value, the method can also suppress ambient noise.
(4) The invention uses square wave power supply to supply power to the light emitting device to realize the simultaneous acquisition of a plurality of wavelength signals. If the two light emitting devices with different wavelengths flicker alternately, only one effective PPG signal is needed at any moment, only one receiving tube is needed to receive the signal, and the signal is separated in AD sampling. The innovation point realizes that one channel adopts multiple signals, and the circuit area consumption is greatly reduced.
In the foregoing description of the specification, reference to the description of "one embodiment/example," "another embodiment/example," or "certain embodiments/examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
While embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.
While the preferred embodiments of the present invention have been illustrated and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. The utility model provides an adopt PPG waveform and heart rate detection system of hardware realization which characterized in that includes:
the infrared photoelectric sensor is used for detecting the pulse waveform of the fingertip of a human body to obtain a pulse signal;
the analog-to-digital converter is used for performing analog-to-digital conversion on the pulse signal to obtain a pulse wave signal;
the pulse wave signal processing module comprises a heart rate hardware counting unit and a heart rate waveform pixel hardware processing unit, wherein the heart rate hardware counting unit is used for calculating a heart rate value according to a pulse wave signal and controlling a display screen to display the heart rate value; the heart rate waveform pixel hardware processing unit is used for controlling the display screen to display the PPG waveform according to the pulse wave signal;
and the display screen is used for displaying the PPG waveform and the heart rate value.
2. The PPG waveform and heart rate detection system realized by hardware according to claim 1, wherein a filter circuit composed of three stages of high-pass, low-pass and high-pass in sequence is arranged on the infrared photoelectric sensor, and the filter circuit is used for filtering a pulse signal.
3. The PPG waveform and heart rate detection system implemented in hardware according to claim 1, wherein the light emitting device on the infrared photoelectric sensor is powered by a pulse sequence with a preset frequency.
4. The PPG waveform and heart rate detection system implemented by hardware according to claim 1, wherein the heart rate hardware counting unit calculates the number of pulses by detecting the rising edge of one pulse period, and calculates the heart rate value according to the number of pulses.
5. The PPG waveform and heart rate detection system implemented by hardware according to claim 4, wherein the heart rate hardware counting unit comprises three registers, namely a first register, a second register and a third register; the counting process is as follows:
determining a value a, wherein the value a is between the peak value and the peak value of the pulse wave signal;
comparing the acquired pulse signal values with a value a one by one, and setting a first register to be 1 when the pulse signal value is more than or equal to a; when the pulse signal value is less than a, setting the first register to be 0;
adding 1 to the numerical value of the second register every time the first register jumps from 0 to 1, and resetting the count value of the second register to 0 when the count value of the second register reaches n;
when the numerical value of the second register is detected to be 0, setting the third register to be 0, and when the numerical value of the second register is detected not to be 0, enabling the third register to count the input clock;
acquiring a time value T of the second register from the value 1 to the value n:
in the formula, CLK is the input clock frequency, c is the counting result of the third register;
and calculating according to the obtained time value to obtain a heart rate value.
6. The PPG waveform and heart rate detection system realized by hardware according to claim 1, wherein the heart rate hardware counting unit controls the display screen to display the heart rate value by:
acquiring a unit display area, a ten-digit display area and a hundred-digit display area on a display screen;
for each display area, coordinate pixels corresponding to ten numbers, namely 0 to 9, are stored in advance;
and after the heart rate value is obtained through calculation, controlling the corresponding coordinate pixel to display according to the heart rate value.
7. The hardware-implemented PPG waveform and heart rate detection system according to claim 1, wherein the heart rate waveform pixel hardware processing unit controls the display screen to display the PPG waveform by:
interacting with a display screen through the FPGA;
and selecting a display area for displaying the PPG waveform in the display screen, mapping the pulse wave signal and the coordinate value of the display area, and obtaining and controlling the corresponding pixel point to display so as to display the PPG waveform in the display screen.
8. The system of claim 3, wherein the pulse wave signal processing module is further configured to separate the pulse wave signal during AD sampling to separate a DC component of the PPG from DC noise of the power supply.
9. The system according to claim 8, wherein when the infrared photoelectric sensor is required to detect pulse wave signals corresponding to multiple light waves with different wavelengths, different pulse wave signals are subsequently separated during AD sampling, so that one channel of detector channel can receive multiple channels of input waveforms simultaneously.
10. The hardware-implemented PPG waveform and heart rate detection system according to claim 1, wherein the display screen is an electronic ink screen.
Priority Applications (1)
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