Infrared Heart Rate Measurement System Based on LabVIEW

A wireless heart rate measurement system is designed and implemented based on LabVIEW as the development platform. The HKG-07B infrared pulse sensor is used to collect ECG signals. After amplification, filtering, shaping, and AD conversion, the signal is displayed through LED to display the heart rate and sent to the PC terminal via wireless. The terminal signal is collected, displayed, and stored by LabVIEW, and the heart rate waveform can be called at any time. The design is small in size, good in real time, and has a friendly human-computer interface.

Heart rate measurement is one of the commonly used medical examination items and an important indicator for human health monitoring. The core chip used in the current home heart rate measurement system is mainly a single-chip microcomputer. Although the products designed by this development method are easy to carry, it is difficult to store the heart rate waveform in real time and effectively. The heart rate test system using LabVIEW can not only measure the heart rate in real time and display the heart rate waveform, but also store the heart rate waveform conveniently, which is convenient for subsequent algorithm processing.

1 System composition and principle

The system uses infrared sensor HKG-07B to collect heart rate signals. After amplification, filtering and A/D conversion, the data is calculated by MCU and displayed by LED. The A/D converted data is sent to the PC terminal via WIFI. LabVIEW is used on the PC terminal to display the waveform, store data and alarm through the network. The system structure diagram is shown in Figure 1.

Figure 1 System structure diagram

2 LABVIEW acquisition display storage module design

The heart rate graph received by the PC is collected and displayed by LABVIEW, and the storage time length can be selected. Its front panel interface is shown in Figure 2.

Figure 2 LabVIEW front panel interface

When collecting data, the serial port will be initialized and checked to see if any data has been received. If not, it will continue to wait. The program flowchart is shown in Figure 3.

Figure 3 Serial port initialization

After setting the serial port parameters, execute the acquisition module, read the data sent by the serial port, convert the received string data into ASCII code, and then convert it into the voltage value. Since the data received by the computer is 8-bit binary, that is, 0 to 255, its corresponding voltage value is (U/255)×5, and is input into the display waveform for display. As shown in Figure 4.

Figure 4 Character conversion

After the string data is converted into ASCII code, an array is created, a waveform is created, and the frequency of the input waveform is detected according to the waveform measurement module. The frequency is multiplied by 60 to get the heart rate per minute, as shown in Figure 5.

Figure 5 Pulse rate calculation

In order to facilitate the later use of historical data, the collected data is saved. The ASCII code is converted into a decimal voltage value and saved in a spreadsheet, as shown in Figure 6.

Figure 6 Storage module

When calling historical data, select the playback mode, read the saved file, convert it into an array, and display the waveform of the selected segment data, as shown in Figure 7.

Figure 7 Playback module

3 Test Results

The results after the system is powered on are shown in Figure 8. From the test results, the heart rate displayed by the LED is slightly different from the heart rate displayed by the PC. This is because the calculation methods of the two are different. The computer uses a longer statistical time to calculate the heart rate value, while the microcontroller uses a shorter statistical time to calculate the heart rate.

Figure 8 System working diagram

Figure 9 Heart rate graph after interference

During the test, it was also found that the heart rate pulse was partially disturbed, and the waveform after interference is shown in Figure 9. Interference includes interference from other signals during signal transmission and reception, and also includes interference from the external environment to the sensor during acquisition. In order to reduce the occurrence of bad signals, the acquisition and filtering circuits can be further improved.

4 Conclusion

The system uses LabVIEW as the platform, uses the Huake HDG-07B infrared sensor to collect heart rate signals, uses AD0809 as the analog-to-digital conversion chip, and uses the USR-WIFI232-B WIFI wireless transceiver module to measure and display heart rate. The test results show that the system has good reliability and can be further processed on the LabVIEW platform.