JPS61154639A - Cardiac pulse detection circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a photoelectric pulse detection circuit used in electronic devices such as electronic wristwatches.

[Conventional technology]

Pulse detection methods include detecting the vibrations in the arteries caused by the heartbeat, and methods that detect the heart sounds caused by the heartbeat.

Methods such as detecting changes in blood volume are used. Particularly in the case of small electronic devices, it is effective to detect changes in vehicle volume using optical means and measure pulse rate and the like from the photoplethysmogram obtained thereby.

For example, LED (light emitting diode)
A light emitting element such as a light emitting element and a light receiving element such as a phototransistor are provided, and the light from one light emitting element is irradiated onto the light receiving element, and the reflected light or transmitted light is incident on the light receiving element, thereby changing the vehicle volume in accordance with the pulse of the blood. is detected as a change in the amount of received light, and the photoplethysmogram obtained is converted into a signal corresponding to the pulse via a filter circuit, amplifier, waveform shaping circuit, etc., and the pulse rate is measured by converting it into a signal corresponding to the pulse. do.

Conventionally, such photoelectric pulse detection circuits.

Keeping a light-emitting element such as an LED lit while pulse detection is a waste of power, so a method of pulse-driving the light-emitting element (see Utility Model Application Publication No. 53-76697) or a light-receiving element can be used to first remove external light sources other than the light-emitting element. A method of determining light illuminance and controlling lighting or non-lighting of a light emitting element depending on whether the external light illuminance is sufficient (see Japanese Patent Application Laid-Open No. 109030/1983)
etc. are being considered.

[Problem that the invention seeks to solve]

In the conventional pulse detection circuit as described above.

Although it can prevent power consumption to some extent.

For example, in order to provide an electronic wristwatch with a pulse detection circuit and operate it on one battery for several years, it is necessary to further reduce power consumption.

[Purpose of the invention]

In view of the above circumstances, it is an object of the present invention to provide a pulse detection circuit that consumes even less power.

[Key points of the invention]

In order to achieve the above object, the present invention includes a light receiving element, a light receiving element driving means for supplying a driving voltage to the light receiving element, and a pulse signal of a predetermined frequency is applied to the light receiving element driving means to pulse drive the light receiving element. The invention is characterized in that it has a control means for performing control as follows.

According to the above means, it is possible to efficiently reduce power consumption on the element side.

[Embodiments of the invention]

Hereinafter, nine embodiments of the present invention will be described in detail with reference to the drawings.

In this embodiment, the pulse rate detection circuit of the present invention is provided in an electronic wristwatch, and the pulse rate is measured by placing a finger on a predetermined position of the electronic wristwatch.

FIG. 2 is a diagram showing the external appearance of a part of the electronic wristwatch used in the present invention. In the figure, a watch case I is provided with a display section 2 for displaying the time, day of the week, pulse rate, etc., a pulse detection sensor 3 on which a finger is placed, and a switch for setting the time and day of the week (not shown). The pulse detection sensor 3 includes an LED 4 which is a light emitting element and a phototransistor 5 which is a light receiving element.

Metal electrodes 5a and 5b are provided outside the LED 4 and the phototransistor 5.

As shown in Fig. 3, the display section 2 consists of a liquid crystal display element 2, which displays the day of the week from Sunday to Saturday or the magnitude of the pulse wave when detecting the pulse, and the display element 7 which displays the time or the number of pulses per minute. It is composed of a display element 8 for displaying images. Normally, when displaying the time on the display element 8, all four digits are used, and when displaying the pulse rate, only the right three digits are used.

FIG. 1 is a circuit diagram of an electronic wristwatch including the pulse detection circuit of the present invention provided in the electronic wristwatch described above. In the figure, a frequency dividing circuit, a clock circuit, which is a circuit for clock functions such as the time and day of the week, a timing signal generator for outputting various timing signals, and the like are provided in a central processing unit (hereinafter referred to as CPU) 9.

The normal time display is 9.32.76 times the crystal oscillator (not shown).
A frequency dividing circuit divides the 8 KHz high frequency signal into a 1 h signal, and a clock circuit converts it into a time signal such as 1 minute 9 seconds and a day of the week signal, and displays the time and time on the display unit 2 via the display driver 10. Display the day of the week.

On the other hand, the pulse detection circuit includes the pulse detection sensor 3 and CP described above.
U9. Current control circuit 14 for LED4. It mainly consists of a current control circuit 15 for a phototransistor 5. When the finger 16 is placed on the metal electrodes 6a, (ib), the metal electrodes 5a, 5
b is conductive and the metal electrode 6a is grounded, so a low signal (
ground potential) is input to the inverter 17. Inverter 1
A high signal is input to 7 by the voltage (■...) normally connected to the resistor R2, but this input signal inverts the output signal of the inverter 17 from a low signal to a high signal, and the high signal is sent to the CPU 9. input.

The CPU 9 uses this input signal to perform the transfer game)T.
It outputs control signals (s, d) and control signals (k) to I, T2, turns on transfer gates (TI and T2), operates voltage regulator 18, and turns on voltage regulator 1.
8 is an operational amplifier (operational amplifier) 11 to 13 connected to the output of the voltage regulator 18.
Supply driving voltage to.

By turning on the transfer gate T+, the emitter of the phototransistor 5 is connected to the current control circuit 15, and when the external light 19 is present and the light transmitted through the finger 16 is input to the phototransistor 5, the emitter of the phototransistor 5 is connected to the current control circuit 15.
A current flows according to the amount of light received. Analog/digital (hereinafter referred to as A/D) via transfer gate T2
A voltage is applied to the input of the converter 20, and at this time A/
A control signal j is also input to the D converter 20 from the CPU 9, and this voltage value is converted into a digital signal by the A/D converter 20 and output to the CPU 9. The CPU 9 compares the input digital signal with data necessary for pulse detection stored in advance in the CPU 9, and if it determines that this digital signal has a value that allows pulse detection, the CPU 9
A pulse-like control signal a is sent from the transfer gate T3 to the transfer gate T3.
is output and transfer gate T3 is turned on.

Turn off.

The emitter voltage of the phototransistor 5 changes as the transfer gate T3 is turned on and off.
Operational amplifier 11 when transfer gate T3 is on. The signal is input to a sampling and hold circuit 21 composed of capacitors CI and C2 and resistors R3 and R4.

The sampling and hold circuit 21 converts the pulse-like waveform shown in FIG. 4(a) into a step-like continuous waveform shown in FIG. Capacitor C3°C4, resistor Ra,
The signal is input to a low-pass filter 22 composed of Rs. The low-pass filter 22 removes the high-frequency ripple included in the input waveform and outputs the waveform as shown in FIG. The signal is input to an AC amplifier circuit 23 composed of a capacitor C5+Ca and resistors R7 and Re. The AC amplifier circuit 23 amplifies the input waveform and sends it to the Schmitt trigger circuit 2.
4, and the Schmitt trigger circuit 24 outputs the same figure (d
) is converted into a rectangular pulse-like pulse signal and output to the CPU 9. The CPU 9 calculates the period (
Pt).

The CPU 9 performs this operation every time each pulse of the pulse signal arrives, calculates the average value of the past three cycle data, and converts the pulse rate per minute from this average value (for example, (60
÷average value of period data)), and the result of this calculation is displayed on the display unit 2 via the display driver 10.

In addition, when calculating the average value of the periodic data mentioned above, each time new periodic data is obtained, it is compared with the past three periodic data, and the new periodic data is within the range of the past three periodic data. When this happens, the oldest data is cleared to calculate the average value, and when it is outside the range, new data is cleared and the previous pulse rate display continues.

On the other hand, if the digital signal input from the A/D converter 20 to the CPU 9 does not have a value that allows pulse detection, the CPU
9, the CPU 9 outputs a control signal C to the transfer gate T4.

Transfer gate Ta is driven. Transfer game) When Ta is turned on, the transistor 25 is turned on and off by the control signal a, current flows through the LED 4 connected to the collector of the transistor 25 and the current control circuit 14 connected to the emitter, and the LED 4 emits light. do. The light from this LED 4 is reflected by the finger 16, and the reflected light is irradiated onto the phototransistor 5 described above. At this time, the transfer gate T3 is already in the on/off driving state, so as in the case where external light is present as described above,
The current flowing through the phototransistor 5, which indicates the change in the amount of received light, is input to the sampling and holding circuit 21 via the transfer gate T3, and is further input to the filter circuit 22. The pulse rate per minute is inputted to the CPU 9 via the AC amplifier circuit 23 and the Schmitt trigger circuit 24, and the pulse rate per minute, which is the calculation result of the CPU 9, is displayed on the display section 2.

Further, the control signal d from the CPU 9 is input to the transfer gate Ts via the inverter 26, and when the control signal d becomes a low signal, the waveform output of the AC amplifier circuit 23 is transferred to the A/D converter via the transfer gate T5. Input to converter 20.

The waveform output is converted into a digital output and input to the CPU 9, and the display element 7 of the second display unit 2 is used to display the magnitude of the pulse wave.

Further, the current control circuit 14 is as shown in FIG.

transfer gate T6 and resistor R9, transfer gate T7 and resistor R+o,) transfer gate TI+
The current control circuit 15 is composed of three series circuits including a resistor R++ and a resistor R++, as shown in FIG. 6(b).

Transfer game) T9 and resistance R+ 2. It is composed of two series circuits: a transfer gate T1o and a resistor R13. Transfer gates Ta to Too are driven by control signals e to i of the CPU 9, respectively.

In the electronic wristwatch having the external appearance and circuit configuration as described above, the operation of detecting the pulse rate will be explained below with reference to the flowchart and table shown in FIG.

When the finger 16 is placed on the metal electrodes 6a, 6b, a high signal is input to the CPU 9 via the inverter 17, as described above, and the CPU 9 initializes each control signal a to y k to a low level. , control signals S, d, h, j, and k are set to high level (step 1). As a result, drive voltage is supplied from the voltage regulator 18 to the operational amplifiers 11 to 13, transfer gates T+ and Too are turned on, the phototransistor 5 is put into operation, and the transfer gate T2 is turned on, so that the A/D converter 20 A voltage value is output according to the amount of light received by the phototransistor 5.

The A/D converter 20 converts this voltage value into 5-bit digital data ("11111" when the voltage is maximum, "oooooo" when it is minimum) as shown in the table below.
”) and output to the CPU 9.

(table) ! Next, the process advances to step 2 and the input data is judged.

As shown in the table, when the input 5-bit data is "oooooo", the CPU 9 determines that there is no external light, moves to step 3, sets the control signal C to high level, turns on the transfer gate T4, and outputs the control signal. The LED 4 is turned on in synchronization with the signal a, and the control WI signal g is set to high level to select the resistor R9 (lkΩ), and the current flowing through the LED 4 is controlled to maximize the amount of light emitted from the LED 4. Also, on the phototransistor 5 side, the control signal is set to high level and R+3 (50Ω) is selected as the load resistance of the phototransistor 5.
The voltage waveform received by the phototransistor 5 at the timing of the control signal a having a pulse width of 300 μsec is increased to the sampling and hold circuit 21.
A control signal having a pulse width of 360 μsec drives the phototransistor 5 on and off. At this time, the timing of the control signals a and b is as shown in the time chart of FIG. 8. The control signal A is driven at a frequency of 128 Hz 60 μsec earlier than the control signal a, and when the light from the LED 4 is input to the phototransistor 5, the phototransistor 5 is in a stable state. Therefore, the waveform is shown in the same figure! A stable output waveform of the phototransistor 5 is obtained as shown in FIG. Furthermore, the control signal d is set to low level and the A/D
The voltage for detecting the level of received light input to the converter 20 is cut off, and the output of the AC amplifier circuit 23 is switched to input.

Next, the 5-bit data input to the CPU 9 is “000”.
10" and "00001", it is determined that the external light is present but the amount of received light is insufficient, and the process of step 4 is performed.Similarly to the above, the control signal C is set to high level and the LE
D4 is turned on in synchronization with the control signal a, and the control signal f is set to high level to select the resistor R+o (10Ω) to make the amount of light emitted by the LED 4 smaller than when the above-mentioned external light is not present.

Also, on the phototransistor 5 side, as in the case where no external light exists, the control signal is set to high level, the load resistance of the phototransistor 5 is set to the resistance R + 3 (50Ω), and the sampling and holding from the phototransistor 5 is performed. The amplitude of the voltage waveform input to the circuit 21 is increased, and a voltage waveform signal is outputted to the sampling and hold circuit 2I at the timing of the control signal a having a pulse width of 150 μsec, thereby generating a control signal having a pulse width of 1210/J sec. The phototransistor is already turned on and off. At this time, the timing of control signals a and b is the ninth
As shown in the figure, the control signal A is driven 60 μsec earlier than the control signal A at a frequency of <128 Hz, and after the phototransistor 5 is in a stable state as described above, the LED 4 is
lights up. Therefore, the output of the phototransistor 5 has a stable output waveform as shown in waveform m. Further, the control signal d is set to low level, the voltage for detecting the level of received light input to the A/D converter 20 is cut off, and the output of the AC width circuit 23 is switched to input.

Next, when the 5-bit data is "00011", it is determined that although external light is present, the amount of received light is somewhat insufficient, and the process of step 5 is performed. Similarly to the above, the control signal C is set to high level, and the LED 4 is turned on in synchronization with the control signal a.
Furthermore, the control signal e is set to high level and resistor R++ (100Ω) is selected as the load resistance of LED4.
Minimize the amount of light emitted by the In addition, the phototransistor 5 side is controlled in the same manner as in step 4 above, and the control signal is set to high level, and the control signal is set to high level for 150 μsec and 210 μsec, respectively.
Control signals a and b having a pulse width of sec are applied to the transfer gates T 3 and T + to increase the amplitude of the voltage waveform input to the sampling and hold circuit 21 and to keep the phototransistor 5 in a stable state.
Turn on D4. Further, the control signal d is set to a low level to cut off the light reception level detection voltage input to the A/D converter 20.

Next, the 5-bit data is "00100" to "1111"
0'', the external light is present and the amount of light received is sufficient, so it is processed in steps and 6, and the control signal C remains at a low level and the LED 4 is turned off.

Controls the phototransistor 5 side. The control of the phototransistor 5 uses the sufficient amount of external light 19 received by the phototransistor 5 since the LED 4 is not lit, and performs the same process as in step 4 above. That is, the control signal is set to high level.

Control signals a and b each 150 μsec, 210
A signal having a pulse width of μsec is applied to the transfer gates T 3 and T +, and the control signal d′ is set to a low level as described above to complete the process of step 6.

Further, when the 5-bit data is "11111", it means that extraneous light is present and the amount of light is sufficiently large, and is processed in step 7. At this time as well, the control signal C remains at a low level to turn off the LED 4, and the control signal i is set to a high level to turn off the phototransistor 5.
The example load resistor R12 (5Ω) is selected, the current flowing through the phototransistor 5 is set as the maximum, and a voltage waveform is input to the sampling and holding circuit 21. In addition, the control signal a
.

b is set in the same manner as in step 6, and the control signal d is set to low level in the same manner as described above to complete the process in step 7.

After any one of the above steps 3 to 7 has been carried out, the process proceeds to step 8, in which the rectangular pulse signal shown in FIG. Display element 8 displays the pulse rate per minute, and display element 9 displays the pulse wave level. This display of the pulse rate and pulse level continues until it is detected in step 9 that the finger 16 is removed from the pulse detection sensor 3. When the finger 16 is removed, the control signal aw k is output under the control of the CPU 9. becomes low level (step 10), and the pulse detection process ends.

As shown in the above operation description, in this embodiment, when detecting the pulse rate, changes in the amount of traffic flowing through the finger 16 are detected by the LED 4. External light 1
The phototransistor 5 detects a change in the amount of reflected light or transmitted light of 9, converts it into a 5-bit digital signal by the A/D converter 20, and inputs it to the CPU 9. In addition to controlling the duty of the transfer gates T1 to Too, the on/off drive of the transfer gates T1 to Too is controlled to reduce the current consumption during pulse rate detection.

That is, by controlling the lighting and non-lighting of the LED 4 depending on the intensity of the external light 19, and controlling the lighting time, the L
To prevent waste of the current consumption flowing through the ED4, by selecting the resistors R9 to R++ of the current control circuit 14, the LED4 is driven with the minimum current value necessary for pulse detection, and furthermore, the phototransistor 5 is driven according to the amount of light received by the phototransistor 5. The drive time of the rephoto transistor 5 is controlled by changing the duty of the pulse width of the control signal 5, and the input signals to the operational amplifiers 11 to 13 are also gate-controlled to the control signal a to efficiently control the pulse rate with low power consumption. It detects numbers.

It goes without saying that the embodiments of the present invention are not limited to those used in the above-described electronic wristwatch, but can be used in other pulse-beating electronic devices having a light-emitting element and a light-receiving element. Furthermore, the digital data output by the A/D converter 20 is not limited to 5 bits, but may use other bit numbers (furthermore, instead of the direct output of the phototransistor 5, the output of the AC amplifier circuit 23 is used as the output of the A/D converter). 20 to determine the driving conditions.

〔Effect of the invention〕

As described in detail above, according to the present invention, the pulse rate can be detected with less power consumption during pulse detection, and in particular, it is possible to reduce the power consumption of driving the light receiving element side.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of an electronic wristwatch including the pulse detection circuit of the present invention, Fig. 2 is an external configuration diagram of a part of the electronic wristwatch, Fig. 3 is a diagram of the configuration of the display section of the electronic wristwatch, and Fig. 4 is a diagram of the electronic wristwatch. Voltage waveform diagram,
FIG. 5 is a block diagram of the current control circuit 14, FIG. 6 is a block diagram of the current control circuit 15, FIG. 7 is a flowchart, and FIGS. 8 and 9 are waveform diagrams of control signals a and b. 2...Display unit, 3...Pulse detection sensor,
4...LED, 5...Phototransistor, 6a, 6b...Metal electrode,
9...CPU, 14.15...Current control circuit, 16...Finger. 19... External light, 20... A/D converter, 21... Sampling hold circuit,
22...filter circuit. 23...AC amplifier circuit, 24...Schmitt trigger circuit, T+~T5...transfer gate. Patent Applicant Casio Computer Co., Ltd. Representative Patent Attorney Yoshiyuki Osuga Figure 2 Figure 3 Figure '4

Claims (8)

[Claims] (1) In a photoelectric pulse detection circuit, a light receiving element, a light receiving element driving means for supplying a driving voltage to the light receiving element, and a pulse signal of a predetermined frequency are applied to the light receiving element driving means to pulse drive the light receiving element. What is claimed is: 1. A pulse detection circuit comprising a control means for controlling the pulse rate as follows. (2) The pulse detection circuit according to claim 1, wherein the control means changes the waveform of a pulse signal applied to the light receiving element driving means in accordance with the output of the light receiving element. (3) The pulse detection circuit according to claim 1, wherein the control means controls the pulse width of the pulse signal applied to the light receiving element driving means in accordance with the output of the light receiving element. (4) The control means performs control such that the pulse width is shortened when the output of the light receiving element is large, and the pulse width is lengthened when the output is small. Pulse detection circuit described in Section 2. (5) The pulse detection circuit according to claim 1, wherein the control means gate-controls the output of the light receiving element in synchronization with a pulse signal for pulse-driving the light receiving element. (6) The light-receiving element receives light from the light-emitting element through a part of the human body, and the control means generates a waveform of a pulse signal for pulse-driving the light-emitting element in accordance with the output of the light-receiving element. 2. The pulse detection circuit according to claim 1, wherein the pulse detection circuit changes the pulse rate. (7) The light-receiving element receives light from the light-emitting element through a part of the human body, and the control means pulses a pulse signal for driving the light-emitting element in accordance with the output of the light-receiving element. 2. The pulse detection circuit according to claim 1, wherein the pulse detection circuit controls the width. (8) The light-receiving element receives light from the light-emitting element through a part of the human body, and the control means pulses a pulse signal for driving the light-emitting element in pulses according to the output of the light-receiving element. The pulse signal for driving the light receiving element has the same frequency as the pulse signal for driving the light emitting element, has a wider pulse width, and is output earlier than the pulse signal for driving the light emitting element. A pulse detection circuit according to claim 1.