Abstract: This paper introduces a design method of intelligent human heart rate detection device with AT89C2051 as the control core. The photoelectric sensor is used to collect the pulse signal of the human body, and the signal processing circuit such as preamplifier amplification, filtering, integral comparison, etc. is converted into a pulse voltage signal, and then the pulse signal is processed by the single chip microcomputer to calculate the heart rate and display. Since the sensor signal is very weak, its amplitude is generally in the order of microvolts to millivolts, and it is mixed with various noises and interferences. Therefore, the preamplifier circuit is required to have high gain, high common mode rejection ratio and other technical indicators. The experimental results show that the system hardware and software design schemes are reasonable, and the micro signal amplification, display and alarm functions are realized. It has the advantages of high measurement sensitivity, good real-time performance and high cost performance.
0 Preface
Heart rate is a very important life information in the human body. Traditional pulse diagnosis has affected the accuracy of heart rate test because of its qualitative and subjective nature, and it has become a constraint factor in the application, development and communication of pulse diagnosis in TCM. In order to improve the accuracy of testing such biomedical signals, it is necessary to combine modern science and technology. At present, there are many instruments for detecting heart rate. Common types of test devices based on pressure sensors, photoelectric sensors, capacitive sensors, and electroacoustic sensors, but there is not much difference in the choice of pulse test sites, for the pulse can be made at the fingertips. There are still relatively few instruments for accurate measurements. The intelligent human heart rate detection device introduced here can realize non-invasive measurement of the human finger end, the test process is simple, the heartbeat frequency can be accurately measured, and the data display and the upper and lower limit alarm functions are realized.
1 device composition and working principle
The system composition is shown in Figure 1. The design takes the single-chip AT89C2051 as the core, and the pulse signal is collected by the photoelectric sensor. After the preamplifier circuit, the filter circuit, the integration and the comparison circuit, the pulse signal related to the pulse is obtained, and the pulse signal is sent as an interrupt signal to the pulse period of the single chip microcomputer. Calculation. Then get the pulse beats per minute (ie heart rate), and display the heart rate on the digital tube, while using the software to achieve the upper and lower limit alarm function, when the measured data exceeds the normal range (such as greater than 180 times / min or less than 45 times / min When an alarm is given to alert the doctor.
Figure 1 Block diagram of intelligent human heart rate detection device
2 device hardware circuit design
2.1 Sensor and signal processing circuit
Since the content of the arterial component in the fingertip tissue of the human body is high, and the thickness of the fingertip is relatively thin compared to other human tissues, the light intensity detected by the finger is relatively large, so the measurement position of the photoelectric pulse sensor is in the human body. fingertip. A pair of infrared emitting and receiving probes are placed on both sides of the finger. When the arterial blood vessels periodically contract and relax with the heart, and the blood volume of the arterial blood vessel changes, the infrared receiving probe receives the contraction with the heart periodically. The diastolic arteries beat the light pulse signal to acquire a heart beat signal.
The sensor for detecting heart rate uses infrared pair tubes HRl068C-5Y2 and PT331C. Since the physiological signals collected from human fingers are very weak, the amplitude is generally in the order of microvolts to millivolts, and a large amount of noise is generated during the test due to limb movements and strong power frequency interference. At the same time, the acquired pulse signal is subjected to high-amplification through the preamplifier circuit, which requires the circuit to have high gain and high common mode rejection ratio, at least 80 dB or more, that is, the integrated operational amplifier has high common mode rejection. For the ratio and the extremely low zero drift, etc., the selected resistance parameters should be as accurate as possible. The amplifier circuit consists of a resistor network and OP07. The sensor and preamplifier circuit are shown in Figure 2.
Figure 2 sensor and preamplifier circuit
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