Development of extremely-small-sized portable recorder for heart rate, body temperature, step rate, and amount of physical activity

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A small-sized (9.2cmx6.0cmx2.5cm) portable device was developed which was able to record heart rate, body temperature, step rate, and amount of physical activity, continuously every minute for 34 hours. Heart rate was derived from the electrocardiogram with affixed electrodes to the chest, body temperature was meastured with an external equipment which converted the resistance of thermistor into frequency signal, step rate was counted from detected vertical acceleration of the center of body gravity with an acceleration sensor, and amount of physical activity was obtained by rectifying the acceleration signal and integrating this wave shape. Electrocardiogram was amplified and filtered simultaneotusly with 3/4 of the quadruple operational amplifier (MC14573), and acceleration signal derived from the sensor IC (ADXL150) was also amplified and filtered with remainder 1/4 of the operational amplifier. Two kinds of analog signal, the potential of analog ground, and a frequency signal were inputted to single chip microcomputer with built-in A-D converter (PIC16C711). Then, the data of heart rate, body temperature, step rate, and amount of physical activity were obtained by the software. Successively, they were written in a cereal EEPROM (24LC65) at an interval of every minute. After recording period, the data stored in the recorder were transmitted to the readout interface as infrared rays, then changed to electrical signal, and transferred to the host computer through the serial port. Moreover the method was also developed to estimate daily energy expenditure accurately by using more than two variables among above mentioned 4 kinds of data.