A wearing detection circuit for a heart rate chest strap

Abstract

The present invention relates to a wearing detection circuit for a heart rate chest strap, and belongs to the technical field of wearable devices. The wearing detection circuit for the heart rate chest strap includes: a processor, a first protective resistor, a second protective resistor, a first electrode sheet, a second electrode sheet, and a differential amplifier; the processor is used to control its first port and second port to output a square wave signal with alternating high and low levels, and based on the return signal received by its third port, calculate the rising voltage amplitude information of the return signal, and determine whether the heart rate chest strap is worn according to the rising voltage amplitude information of the return signal. The detection circuit for the heart rate chest strap provided in the present application can effectively avoid the error influence caused by the heart rate chest strap being taken off after being soaked in sweat and the heart rate chest strap being worn on dry skin through waveform characteristics, thereby improving the detection accuracy.

Description

Technical Field

[0001] The invention belongs to the technical field of wearable devices and relates to a wearing detection circuit of a heart rate chest belt. Background Art

[0002] Heart rate chest straps are widely used in sports such as running, cycling, and swimming, as well as in medical fields such as physical fitness monitoring for people in special industries. Athletes tie the heart rate chest strap around their chests. The two electrodes on the heart rate chest strap come into contact with the skin to collect the electromyographic signals emitted by the heart beat, which are then converted into heart rate after being processed by an algorithm. Heart rate chest straps are wearable devices, which are usually designed to be small and thin to avoid interfering with a person's normal movements, and use batteries to power the circuit part of the heart rate chest strap. The limited battery capacity requires that the heart rate chest strap needs to operate with the lowest possible power consumption, so when the chest strap is not worn, it needs to be turned off or put into sleep mode to extend the battery life.

[0003] Commercially available chest heart rate monitors widely use the state of the two ends of the electrode sheet to determine whether the chest heart rate monitor is worn by the human body. Because the human body has a lower electrical conductivity than the air, the impedance of the two ends of the electrode sheet changes after the two electrodes of the chest heart rate monitor touch the skin. The chest heart rate monitor determines whether the chest heart rate monitor is worn by the human body by monitoring this impedance change. Figure 1 As shown, the existing heart rate chest strap provides a wearing detection method, wherein the electrode sheet 1 is connected to a fixed voltage through a protective resistor, and the electrode sheet 2 is connected to a reference ground signal. When the human body is not in contact with the electrode sheet 1 and the electrode sheet 2, there is a fixed voltage between the electrode sheet 1 and the electrode sheet 2. When the human body is in contact with the electrode sheet 1 and the electrode sheet 2 at the same time, that is, when the human body is wearing it, the voltage across the electrode sheet 1 and the electrode sheet 2 is the voltage divided by the human body impedance relative to the protective resistor. This voltage is lower than the fixed voltage. According to the voltage change across the electrode sheet 1 and the electrode sheet 2, it can be judged whether the human body is wearing a heart rate chest strap.

[0004] However, the study found that the above method has the problem of low wearing detection accuracy. Specifically, first, the heart rate chest strap is a flexible belt made of fabric. After the athlete sweats, the heart rate chest strap will absorb sweat. The chest strap soaked in sweat is conductive, which will cause the insulation resistance between the two electrode sheets to decrease. After the athlete takes off the chest strap, due to the decrease in insulation resistance, the voltage between electrode sheet 1 and electrode sheet 2 will deviate from that when it is completely electrically insulated, which will cause the wearing detection function to mistakenly judge that the human body is still wearing it, so the heart rate chest strap continues to be maintained in a working state, consuming battery power. Second, there is a stratum corneum on the surface of human skin, and the conductivity of the stratum corneum is poor. The conductivity of the human body of athletes before and after sweating differs by more than 10 times. In the above method, the athlete has the problem that in the early stage of exercise, due to the dry skin and poor conductivity, the voltage between electrode sheet 1 and electrode sheet 2 is close to the complete electrical insulation voltage, which will cause the wearing detection to mistakenly judge that the human body is not wearing the heart rate chest strap, so the heart rate chest strap is maintained in a dormant state, resulting in the heart rate chest strap not calculating the heart rate when worn, thereby affecting the user experience. Summary of the invention

[0005] In order to solve the above-mentioned problems in the prior art, the present invention provides a wearing detection circuit for a heart rate chest strap.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] In a first aspect, the present application provides a wearing detection circuit for a heart rate chest strap, comprising: a processor, a first protective resistor, a second protective resistor, a first electrode sheet, a second electrode sheet and a differential amplifier; the first protective resistor is respectively connected to the first electrode sheet and the first port of the processor; the second protective resistor is respectively connected to the second electrode sheet and the second port of the processor, the first electrode sheet is also connected to the first input end of the differential amplifier, the second electrode sheet is also connected to the second input end of the differential amplifier, and the output end of the differential amplifier is connected to the third port of the processor; the processor is used to control its first port and second port to output a square wave signal with alternating high and low levels, and based on the return signal received by its third port, calculate the rising voltage amplitude information of the return signal, and determine whether the heart rate chest strap is worn according to the rising voltage amplitude information of the return signal; wherein, when the first port of the processor outputs a high level, the second port of the processor outputs a low level; when the second port of the processor outputs a high level, the first port of the processor outputs a low level.

[0008] Optionally, the rising voltage amplitude information of the return signal is the amplitude ratio of the return signal at 1 / 2 of the time when the output signal is at a high level; the processor is also specifically used to determine that the heart rate chest strap is not worn when it is calculated that the amplitude ratio of the return signal at 1 / 2 of the time when the output signal is at a high level is higher than a first threshold, and to determine that the heart rate chest strap is worn when it is calculated that the amplitude ratio of the return signal at 1 / 2 of the time when the output signal is at a high level is lower than the first threshold.

[0009] Optionally, the rising voltage amplitude information of the return signal is the amplitude ratio of the return signal at 1 / 4 of the time when the output signal is at a high level; the processor is also specifically used to determine that the heart rate chest strap is not worn when it is calculated that the amplitude ratio of the return signal at 1 / 4 of the time when the output signal is at a high level is higher than a second threshold, and to determine that the heart rate chest strap is worn when it is calculated that the amplitude ratio of the return signal at 1 / 4 of the time when the output signal is at a high level is lower than the second threshold.

[0010] Optionally, the wearing detection circuit of the heart rate chest strap also includes an acceleration sensing device; the acceleration sensing device is connected to the fourth port of the processor; and the processor is configured to detect the wearing condition of the heart rate chest strap in response to a detection signal after the acceleration sensing device is triggered.

[0011] Optionally, the processor is further configured to be awakened once every first periodic interval, and after being awakened each time, detect the wearing condition of the heart rate chest belt.

[0012] Optionally, the processor is also configured to extend the interval time in a step-by-step manner after the heart rate chest strap is not collected as being worn for n consecutive times; wherein, when the heart rate chest strap is not collected as being worn for q consecutive times, the processor automatically shuts down; wherein, q is an integer multiple of n, and q is greater than n; and n is a positive number.

[0013] Optionally, the wearing detection circuit of the heart rate chest strap also includes: a first resistor and a second resistor; the first resistor is connected in series between the first electrode sheet and the first input end of the differential amplifier; the second resistor is connected in series between the second electrode sheet and the second input end of the differential amplifier; the first resistor and the second resistor are used to adjust the amplification factor of the differential amplifier.

[0014] Optionally, the wearing detection circuit of the heart rate chest strap also includes: a third resistor, a fourth resistor, a first capacitor and a second capacitor; the third resistor and the first capacitor are connected in series between the first electrode sheet and the first input end of the differential amplifier; the fourth resistor and the second capacitor are connected in series between the second electrode sheet and the second input end of the differential amplifier; the third resistor, the fourth resistor, the first capacitor and the second capacitor are used to adjust the amplification factor of the differential amplifier.

[0015] The beneficial effects of the embodiments of the present application include:

[0016] The wearing detection circuit of the heart rate chest strap provided by the embodiment of the present application is adopted. Since the processor controls its own first port and second port to output a square wave signal with alternating high and low levels, when the human skin is not in contact with the electrode sheet, the signal received from the third port of the processor is also a corresponding alternating signal, that is, a square wave signal with a rectangular waveform. However, when the human body contacts the electrode sheet, the electrode sheet and the human body form a contact resistance. At the same time, due to the parasitic capacitance of the human body itself, there is an equivalent circuit between the first electrode sheet and the second electrode sheet in which the human body resistance and the parasitic capacitance are connected in parallel, thereby causing the alternating signal at both ends of the first electrode sheet and the second electrode sheet to be distorted and deformed into an approximately triangular wave signal. It can be seen that in the application process of the above-mentioned heart rate chest strap, whether it is worn or not, there is a significant difference in the signal waveform detected by the processor. Therefore, the embodiment of the present application receives the return signal through its own third port, calculates the rising voltage amplitude information of the return signal, and determines whether the heart rate chest strap is worn according to the rising voltage amplitude information of the return signal. After testing, even if the heart rate chest strap is taken off after being soaked with sweat, the overall waveform of the signal received by the processor is still similar to a rectangular square wave, and even if the heart rate chest strap is worn on dry skin, the overall waveform of the signal received by the processor is still similar to a triangular wave. Therefore, the embodiment of the present application can distinguish the above states by judging the rising voltage amplitude change information of the returned signal, thereby effectively solving the problem of low measurement accuracy caused by voltage judgment in the prior art.

[0017] In summary, the embodiment of the present application provides a new detection circuit for a chest heart rate strap, in which both electrode sheets are connected to a port (a first port and a second port) of a processor through a protective resistor, and the processor outputs a square wave signal of alternating high and low levels by controlling its own first port and second port, thereby being able to utilize the different waveform characteristics generated by the human body after contacting the chest heart rate strap to effectively detect whether the human body is wearing the chest heart rate strap. That is, the new detection circuit for a chest heart rate strap provided by the embodiment of the present application can effectively avoid the error caused by the chest heart rate strap being taken off after being soaked in sweat and being worn on dry skin through the waveform characteristics, thereby improving the detection accuracy. At the same time, it can avoid the detection function from mistakenly judging that the human body is still wearing it, thereby continuing to maintain the chest heart rate strap in a working state, consuming battery power, and improving the user experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A circuit diagram of a heart rate chest strap provided by the prior art;

[0019] Figure 2 A circuit diagram of a first heart rate chest strap wearing detection circuit provided by an embodiment of the present invention;

[0020] Figure 3 A circuit diagram of a second heart rate chest strap wearing detection circuit provided by an embodiment of the present invention;

[0021] Figure 4 A circuit diagram of a third heart rate chest strap wearing detection circuit provided by an embodiment of the present invention;

[0022] Figure 5 A circuit diagram of a fourth heart rate chest strap wearing detection circuit provided by an embodiment of the present invention;

[0023] Figure 6 A waveform diagram of a return signal corresponding to a heart rate chest strap provided in an embodiment of the present invention when the chest strap is dry and not worn by a human body;

[0024] Figure 7 A waveform diagram of a return signal corresponding to a heart rate chest strap provided in an embodiment of the present invention when the chest strap is wet and not worn by a human body;

[0025] Figure 8 A waveform diagram of a return signal corresponding to a heart rate chest strap provided in an embodiment of the present invention when the chest strap is dry and worn on dry skin;

[0026] Fig. 9 A waveform diagram of a return signal corresponding to a heart rate chest strap provided in an embodiment of the present invention when the chest strap is dry and worn on wet skin;

[0027] Fig.10A waveform diagram of a return signal corresponding to a heart rate chest strap provided in an embodiment of the present invention when the chest strap is wet and worn on wet skin. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] The study found that the wearing detection method provided by the existing heart rate chest strap has the problem of low wearing detection accuracy. Specifically, first, the heart rate chest strap is a flexible belt woven from fabric, and after the athlete sweats. The heart rate chest strap will absorb sweat. The chest strap soaked in sweat is conductive, which will cause the insulation resistance between the two electrode sheets to decrease. After the athlete takes off the chest strap, due to the decrease in insulation resistance, the voltage between electrode sheet 1 and electrode sheet 2 will deviate from that when it is completely electrically insulated, which will cause the wearing detection function to mistakenly judge that the human body is still wearing it, and therefore continue to maintain the heart rate chest strap in a working state, consuming battery power. Second, there is a stratum corneum on the surface of human skin, and the conductivity of the stratum corneum is poor. The conductivity of the athlete's body before and after sweating differs by more than 10 times. The above method has the problem that in the early stage of exercise, due to the dry skin and poor conductivity of athletes, the voltage between electrode sheet 1 and electrode sheet 2 is close to the complete electrical insulation voltage, which may cause the wearing detection to mistakenly judge that the person is not wearing a heart rate chest strap, so the heart rate chest strap is maintained in a dormant state, resulting in the heart rate chest strap not calculating the heart rate when worn, thereby affecting the user experience.

[0030] In view of the above problems, the present application provides the following embodiments to solve them:

[0031] See also Figure 2 An embodiment of the present application provides a wearing detection circuit for a heart rate chest strap, including: a processor 10, a first electrode sheet 20, a second electrode sheet 30, a first protection resistor 40, a second protection resistor 50 and a differential amplifier 60.

[0032] In terms of connection relationship, the first protection resistor 40 is respectively connected to the first electrode sheet 20 and the first port (IO1) of the processor 10; that is, the first protection resistor 40 is connected between the first electrode sheet 20 and the first port of the processor 10; the second protection resistor 50 is respectively connected to the second electrode sheet 30 and the second port (IO2) of the processor 10, that is, the second protection resistor 50 is connected between the second electrode sheet 30 and the second port of the processor 10.

[0033] The first electrode sheet 20 is also connected to the first input terminal of the differential amplifier 60, the second electrode sheet 30 is also connected to the second input terminal of the differential amplifier 60, and the output terminal of the differential amplifier 60 is connected to the third port (IO3) of the processor 10. In addition, when the heart rate chest strap is in use, the first electrode sheet 20 and the second electrode sheet 30 are used to contact the skin of the human body.

[0034] The processor 10 may be a central processing unit (CPU), a microcontroller unit (MCU), or other general-purpose processors, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or the processor may be any conventional processor, etc.

[0035] In terms of control function, the processor 10 is used to control its first port and second port to output a square wave signal with alternating high and low levels, and based on the return signal received by its third port, calculate the rising voltage amplitude information of the return signal, and determine whether the heart rate chest strap is worn based on the rising voltage amplitude information of the return signal.

[0036] The above-mentioned rising voltage amplitude information of the return signal can be understood as the degree of change of the rising waveform in the waveform of the return signal at the same time interval.

[0037] Among them, when the first port of the processor 10 outputs a high level, the second port of the processor 10 outputs a low level; when the second port of the processor 10 outputs a high level, the first port of the processor 10 outputs a low level. In other words, after the processor 10 is awakened, it controls IO1 to output a square wave signal with alternating high and low levels, and controls IO2 to output a square wave signal with alternating high and low levels. When IO1 is at a high level, IO2 is at a low level, and when IO1 is at a low level, IO2 is at a high level, and so on.

[0038] The first protection resistor 40 and the second protection resistor 50 can effectively prevent damage to the circuit or human body caused by excessive current or short circuit, thereby improving the safety of the product.

[0039] The principle of the wearing detection circuit of the heart rate chest strap provided in the embodiment of the present application is explained below.

[0040] The wearing detection circuit of the heart rate chest strap provided by the embodiment of the present application is adopted. Since the processor 10 controls its first port and second port to output a square wave signal with alternating high and low levels, when the human skin is not in contact with the electrode sheet, the signal received from the third port of the processor 10 is also a corresponding alternating signal, that is, a square wave signal with a rectangular waveform. However, when the human body contacts the electrode sheet, the electrode sheet and the human body form a contact resistance. At the same time, due to the parasitic capacitance of the human body itself, there is an equivalent circuit between the first electrode sheet 20 and the second electrode sheet 30 in which the human body resistance and the parasitic capacitance are connected in parallel, thereby causing the alternating signal at both ends of the first electrode sheet 20 and the second electrode sheet 30 to be distorted and deformed into an approximately triangular wave signal. It can be seen that in the application process of the above-mentioned heart rate chest strap, whether it is worn or not, there is a significant difference in the signal waveform detected by the processor 10. Therefore, the embodiment of the present application calculates the rising voltage amplitude information of the return signal through the return signal received by its third port, and determines whether the heart rate chest strap is worn according to the rising voltage amplitude information of the return signal. After testing, it was found that even if the heart rate chest strap was taken off after being soaked with sweat, the overall waveform of the signal received by the processor 10 was still similar to a rectangular square wave, and even if the heart rate chest strap was worn on dry skin, the overall waveform of the signal received by the processor 10 was still similar to a triangular wave. Therefore, the embodiment of the present application can distinguish the above states by judging the rising voltage amplitude change information of the return signal, thereby effectively solving the problem of low measurement accuracy caused by voltage judgment in the prior art.

[0041] In summary, the embodiment of the present application provides a new detection circuit for a chest heart rate strap, in which both electrode sheets are connected to a port (first port and second port) of the processor 10 through a protective resistor, and the processor 10 controls its first port and second port to output a square wave signal with alternating high and low levels, thereby being able to utilize the different waveform characteristics generated by the human body after contacting the chest heart rate strap to effectively detect whether the human body is wearing the chest heart rate strap. That is, the new detection circuit for the chest heart rate strap provided by the embodiment of the present application can effectively avoid the error caused by the chest heart rate strap being taken off after being soaked in sweat and being worn on dry skin through the waveform characteristics, thereby improving the detection accuracy. At the same time, it can avoid the detection function from mistakenly judging that the human body is still wearing it, thereby continuing to maintain the chest heart rate strap in a working state, consuming battery power, and improving the user experience.

[0042] Optionally, the rising voltage amplitude information of the return signal is the amplitude ratio of the return signal at 1 / 2 of the time when the output signal is at a high level. Accordingly, the processor 10 is further specifically configured to determine that the chest strap is not worn when the amplitude ratio of the return signal at 1 / 2 of the time when the output signal is at a high level is calculated to be higher than a first threshold, and to determine that the chest strap is worn when the amplitude ratio of the return signal at 1 / 2 of the time when the output signal is at a high level is calculated to be lower than the first threshold.

[0043] It should be noted that the amplitude ratio of the above-mentioned return signal at 1 / 2 of the time when the output signal is at a high level can be understood as the ratio of the voltage value corresponding to the 1 / 2 time node of the rising voltage waveform (rising edge) to the voltage of the rising voltage waveform (the moment when the rising edge jumps to the falling edge).

[0044] Taking the output of a 1kHz high-low level alternating square wave signal as an example, the amplitude ratio of the return signal of the heart rate chest strap A corresponding to the human body when not wearing it in various states at 1 / 2 of the output signal time when the output signal is at a high level is in the range of 0.88~1; the amplitude ratio of the return signal of the heart rate chest strap A corresponding to the human body when wearing it in various states at 1 / 2 of the output signal time when the output signal is at a high level is in the range of 0.44~0.6. Then the above-mentioned first threshold value can be set between 0.6 and 0.88. For example, the first threshold value is 0.65. In actual applications, the processor 10 is used to determine that the heart rate chest strap is not worn when the amplitude ratio of the return signal at 1 / 2 of the output signal time when the output signal is at a high level is higher than 0.65, and to determine that the heart rate chest strap is worn when the amplitude ratio of the return signal at 1 / 2 of the output signal time when the output signal is at a high level is less than 0.65.

[0045] Of course, the above is only an example, and the first threshold can be set according to different heart rate chest straps and requirements in the application.

[0046] Optionally, the rising voltage amplitude information of the return signal is the amplitude ratio of the return signal at 1 / 4 of the time when the output signal is at a high level. Accordingly, the processor 10 is further specifically configured to determine that the chest strap is not worn when the amplitude ratio of the return signal at 1 / 4 of the time when the output signal is at a high level is calculated to be higher than a second threshold, and to determine that the chest strap is worn when the amplitude ratio of the return signal at 1 / 4 of the time when the output signal is at a high level is calculated to be lower than the second threshold.

[0047] It should be noted that the amplitude ratio of the above return signal at 1 / 4 of the time when the output signal is high can be understood as the ratio of the voltage value corresponding to the 1 / 4 time node of the rising voltage waveform (rising edge) to the voltage of the rising voltage waveform (the moment when the rising edge jumps to the falling edge). Or, the amplitude ratio of the above return signal at 1 / 4 of the time when the output signal is high can be understood as the ratio of the voltage value corresponding to the 1 / 4 time node of the rising voltage waveform (rising edge) to the voltage value corresponding to the 1 / 2 time node of the rising voltage waveform (rising edge).

[0048] Taking the output of a 1kHz high-low level alternating square wave signal as an example, the return signal corresponding to the heart rate chest strap A in various states when the human body is not wearing it has an amplitude ratio of 0.77 to 1 at 1 / 4 of the output signal time when the output signal is high; the return signal corresponding to the heart rate chest strap A in various states when the human body is wearing it has an amplitude ratio of 0.46 to 0.60 at 1 / 4 of the output signal time when the output signal is high. Then the above-mentioned second threshold value can be set between 0.60 and 0.77. For example, the second threshold value is 0.68. In actual applications, the processor 10 is used to determine that the heart rate chest strap is not worn when the calculated return signal has an amplitude ratio of more than 0.68 at 1 / 4 of the output signal time when the output signal is high, and to determine that the heart rate chest strap is worn when the calculated return signal has an amplitude ratio of less than 0.68 at 1 / 4 of the output signal time when the output signal is high.

[0049] Of course, the above is only an example, and the second threshold can be set according to different heart rate chest straps and requirements in the application.

[0050] Optionally, see Figure 3 The wearing detection circuit of the heart rate chest strap also includes an acceleration sensing device 70; the acceleration sensing device 70 is connected to the fourth port (IO4) of the processor 10.

[0051] The processor 10 is also configured to detect the wearing condition of the heart rate chest strap in response to the detection signal after the acceleration sensing device 70 is triggered.

[0052] The acceleration sensing device 70 mentioned above may be an acceleration sensor, a gyroscope, a vibration sensor, etc., which is not limited in the present application.

[0053] It can be seen that the embodiment of the present application can detect whether there is a user touch action by setting an acceleration sensing device 70. If the user has a touch action, the acceleration sensing device 70 wakes up the processor 10 to detect the wearing condition of the heart rate chest strap. This method can reduce the power consumption of the heart rate chest strap, and the processor 10 does not need to wake up and detect according to a fixed period.

[0054] In addition, the acceleration sensing device 70 can also be configured to provide other specific functions, such as triggering an alarm function when abnormal movements of the user are detected. For example, after detecting that the user is wearing a heart rate chest strap, the acceleration sensing device 70 can still perform continuous or intermittent detection, and trigger an alarm function when the user is detected to have fallen.

[0055] Optionally, in one embodiment, when the heart rate chest strap is not provided with the acceleration sensing device 70, the processor 10 is further configured to be awakened once every first periodic interval, and after being awakened each time, detect the wearing condition of the heart rate chest strap.

[0056] The first periodic interval can be set according to actual conditions, such as 1s, 10s, 30s, etc. This implementation can provide a periodic trigger detection mechanism, thereby reducing power consumption and extending the battery life of the heart rate chest strap, that is, the intermittent working mode can significantly reduce the overall power consumption of the device.

[0057] Optionally, the processor 10 is further configured to extend the interval time in a step-by-step manner after the heart rate chest belt is not collected for n consecutive times when the chest belt is in the wearing state;

[0058] When the heart rate chest strap is not collected for q consecutive times in the wearing state, it is automatically shut down; wherein q is an integer multiple of n, and q is greater than n; and n is a positive number.

[0059] For example, n is 5, q is 15, and initially, the processor 10 has a collection interval of 1 second. If the processor 10 fails to collect the heart rate chest strap being worn for 5 consecutive times, the collection interval is extended to 5 seconds. After the first extension, if the processor 10 fails to collect the heart rate chest strap being worn for 5 consecutive times, the collection interval is further extended to 15 seconds. After the second extension, if the processor 10 fails to collect the heart rate chest strap being worn for 5 consecutive times, the processor 10 automatically shuts down.

[0060] It should be noted that the stepwise extension of the interval time can be understood as gradually extending the interval time according to a preset stepwise strategy. After each adjustment, the collection frequency will be lower than the previous one until it is automatically shut down.

[0061] In summary, the embodiment of the present application provides a method for adjusting the collection interval in stages and an automatic shutdown function, so that when the heart rate chest strap is not worn for a long time, power can be saved and the service life of the heart rate chest strap can be extended. The strategy of step-by-step reduction of the collection interval can reduce the possibility of misjudgment and improve the accuracy and reliability of the device.

[0062] Optionally, the wearing detection circuit of the heart rate chest strap further includes: a first adjustment module and a second adjustment module.

[0063] The first adjustment module is connected in series between the first electrode sheet 20 and the first input terminal of the differential amplifier 60. The second adjustment module is connected in series between the second electrode sheet 30 and the second input terminal of the differential amplifier 60. The first adjustment module and the second adjustment module are used to adjust the gain of the differential amplifier 60.

[0064] See also Figure 4 In one embodiment, the first adjustment module includes a first resistor 81 ; the second adjustment module includes a second resistor 91 .

[0065] The first resistor 81 is connected in series between the first electrode sheet 20 and the first input terminal of the differential amplifier 60. The second resistor 91 is connected in series between the second electrode sheet 30 and the second input terminal of the differential amplifier 60. The first resistor 81 and the second resistor 91 are used to adjust the gain of the differential amplifier 60.

[0066] In practical applications, different resistance values ​​of the first resistor 81 and the second resistor 91 may be set to adjust different amplification factors.

[0067] See also Figure 5 In one embodiment, the first adjustment module includes a third resistor 82 and a first capacitor 83 ; the second adjustment module includes a fourth resistor 92 and a second capacitor 93 .

[0068] The third resistor 82 and the first capacitor 83 are connected in series between the first electrode sheet 20 and the first input terminal of the differential amplifier 60 .

[0069] The fourth resistor 92 and the second capacitor 93 are connected in series between the second electrode sheet 30 and the second input terminal of the differential amplifier 60 .

[0070] The third resistor 82 , the fourth resistor 92 , the first capacitor 83 and the second capacitor 93 are used to adjust the gain of the differential amplifier 60 .

[0071] In practical applications, different resistance values ​​of the third resistor 82 and the fourth resistor 92 and different capacitance values ​​of the first capacitor 83 and the second capacitor 93 may be set to adjust different amplification factors.

[0072] The principle of the wearing detection circuit of the heart rate chest strap provided in the embodiment of the present application is explained below in combination with specific experiments.

[0073] See also Figure 6~Figure 10 , Figures 6 to 10 A schematic diagram of waveforms corresponding to different dry and wet state information between a heart rate chest strap and a human body is shown.

[0074] in, Figure 6 The waveform diagram of the return signal corresponding to the heart rate chest strap when it is dry and not worn by the human body is shown; Figure 7The waveform diagram of the return signal corresponding to the heart rate chest strap when it is wet and not worn by the human body is shown; Figure 8 The waveform diagram of the return signal corresponding to the heart rate chest strap when it is dry and worn on dry skin is shown; Fig. 9 The waveform diagram of the return signal corresponding to the heart rate chest strap when it is dry and worn on wet skin is shown; Fig.10 The waveform diagram of the return signal corresponding to the heart rate chest strap being wet and worn on wet skin is shown.

[0075] from Figure 6~Figure 10 It can be seen from the display that when the human body is not wearing the device, the return waveform presents a rectangular square wave or a rectangular square wave, and when the human body is not wearing the device, the return waveform presents a triangular wave or a triangular wave. Therefore, it is possible to distinguish whether the user is wearing the device based on the amplitude change of the rising edge at the same time.

[0076] The specific principles are:

[0077] When the human body contacts the electrode sheet, the electrode sheet and the human body form a contact resistance. At the same time, due to the parasitic capacitance of the human body, an equivalent circuit of a resistor and a capacitor in parallel exists between the first electrode sheet and the second electrode sheet.

[0078] Due to the existence of parasitic capacitance, the alternating square wave signal between the first electrode sheet and the second electrode sheet will be distorted into an exponential function as shown in the following formula:

[0079] ;

[0080] in, Indicates the DC voltage division formed by the human body resistance and the protection resistance in the circuit; It represents the zero state and zero input response of the first-order circuit composed of human parasitic capacitance and protection resistance. It represents the parallel connection of human body resistance and protection resistance in the current. represents the parasitic capacitance of the human body, represents the time constant; Representation and and The corresponding voltage; Represents the DC voltage division formed by the human body resistance and the protective resistance in the circuit.

[0081] The signal After being amplified by a differential amplifier, it is collected by the processor's ADC (Analog-to-Digital Converter).

[0082] When the chest strap is soaked with sweat or the skin is dry, the resistance at both ends of the chest strap may be abnormal. The value varies greatly. Determined by the parasitic capacitance and protection resistance of the human body. These two items are not greatly affected by the skin condition and whether the heart rate belt is wet. Therefore, this feature is relatively stable.

[0083] In addition, after actual testing, the heart rate chest strap product provided in the embodiment of the present application can accurately identify the wearing and removal of the chest strap when the skin is dry and when the heart rate chest strap is soaked with sweat through a low-power differential amplifier, and the power consumption is within 1mA.

[0084] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0085] References to "one embodiment" or "some embodiments" etc. described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0086] In the description of the embodiments of the present invention, it needs to be understood that terms such as “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “center”, “top”, “bottom”, “top”, “bottom”, “inside”, “outside”, “inside”, and “outside” indicate orientation or positional relationships.

[0087] In the description of the embodiments of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "install", "connect", "connect", and "assemble" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0088] In the description of the embodiments of the present invention, specific features, structures, materials or characteristics may be combined in a suitable manner in any one or more embodiments or examples.

[0089] In the description of the embodiments of the present invention, it should be understood that "-" and "~" represent a range between two values, and the range includes the endpoints. For example, "AB" represents a range greater than or equal to A and less than or equal to B. "A~B" represents a range greater than or equal to A and less than or equal to B.

[0090] In the description of the embodiments of the present invention, the term "and / or" herein is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " herein generally indicates that the associated objects before and after are in an "or" relationship.

[0091] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A heart rate chest strap wearing detection circuit, characterized in that: include: A processor, a first protection resistor, a second protection resistor, a first electrode sheet, a second electrode sheet, and a differential amplifier; The first protection resistor is connected to the first electrode sheet and the first port of the processor respectively; the second protection resistor is connected to the second electrode sheet and the second port of the processor respectively, the first electrode sheet is also connected to the first input terminal of the differential amplifier, the second electrode sheet is also connected to the second input terminal of the differential amplifier, and the output terminal of the differential amplifier is connected to the third port of the processor; The processor is used to control its first port and second port to output a square wave signal with alternating high and low levels, and based on the return signal received by its third port, calculate the rising voltage amplitude information of the return signal, and determine whether the heart rate chest belt is worn according to the rising voltage amplitude information of the return signal; When the first port of the processor outputs a high level, the second port of the processor outputs a low level; when the second port of the processor outputs a high level, the first port of the processor outputs a low level.

2. The wearing detection circuit of the heart rate chest strap according to claim 1, characterized in that: The rising voltage amplitude information of the return signal is the amplitude ratio of the return signal at 1 / 2 of the time when the output signal is at a high level; The processor is also specifically used to determine that the heart rate chest strap is not worn when it is calculated that the amplitude ratio of the return signal at 1 / 2 of the time when the output signal is at a high level is higher than a first threshold, and to determine that the heart rate chest strap is worn when it is calculated that the amplitude ratio of the return signal at 1 / 2 of the time when the output signal is at a high level is lower than the first threshold.

3. The wearing detection circuit of the heart rate chest strap according to claim 1, characterized in that: The rising voltage amplitude information of the return signal is the amplitude ratio of the return signal at 1 / 4 of the time when the output signal is at a high level; The processor is also specifically used to determine that the heart rate chest strap is not worn when it is calculated that the amplitude ratio of the return signal at 1 / 4 of the time when the output signal is at a high level is higher than a second threshold, and to determine that the heart rate chest strap is worn when it is calculated that the amplitude ratio of the return signal at 1 / 4 of the time when the output signal is at a high level is lower than the second threshold.

4. The wearing detection circuit of the heart rate chest strap according to claim 1, characterized in that: The wearing detection circuit of the heart rate chest strap also includes an acceleration sensing device; The acceleration sensing device is connected to the fourth port of the processor; The processor is configured to detect the wearing condition of the heart rate chest belt in response to a detection signal after the acceleration sensing device is triggered.

5. The wearing detection circuit of the heart rate chest strap according to claim 1, characterized in that: The processor is also configured to be awakened once at every first periodic interval, and after being awakened each time, detect the wearing condition of the heart rate chest belt.

6. The wearing detection circuit of the heart rate chest strap according to claim 5, characterized in that: The processor is further configured to extend the interval time in a step-by-step manner after the heart rate chest belt is not collected for n consecutive times when the chest belt is in a wearing state; When the heart rate chest strap is not collected for q consecutive times in the wearing state, it is automatically shut down; wherein q is an integer multiple of n, and q is greater than n; and n is a positive number.

7. The wearing detection circuit of the heart rate chest strap according to claim 1, characterized in that: The wearing detection circuit of the heart rate chest strap also includes: a first resistor and a second resistor; The first resistor is connected in series between the first electrode sheet and the first input terminal of the differential amplifier; The second resistor is connected in series between the second electrode sheet and the second input terminal of the differential amplifier; The first resistor and the second resistor are used to adjust the gain of the differential amplifier.

8. The wearing detection circuit of the heart rate chest strap according to claim 1, characterized in that: The wearing detection circuit of the heart rate chest strap also includes: a third resistor, a fourth resistor, a first capacitor and a second capacitor; The third resistor and the first capacitor are connected in series between the first electrode sheet and the first input terminal of the differential amplifier; The fourth resistor and the second capacitor are connected in series between the second electrode sheet and the second input terminal of the differential amplifier; The third resistor, the fourth resistor, the first capacitor and the second capacitor are used to adjust the gain of the differential amplifier.

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