Design and Implementation of a Low-Energy Wearable Physiological Sensor

• Main Authors: Chen, I Hsuan, 陳易萱
• Other Authors: Ma, Hsi Pin
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/sv7tr6

碩士 === 國立清華大學 === 電機工程學系 === 105 === In this thesis, a wearable sensing device is proposed. The system is microcontroller-based and features Bluetooth Low Energy (BLE) technology for wireless transmission. Three types of sensors are integrated in our system. A wearable physiological device is developed to record single-lead electrocardiography (ECG) signals, respiration signals, and the motion trackings of users. An ECG and respiration sensor is adapted to detect single-lead ECG signal and thorax impedance variation caused by respiration of the users. The sampling rate is 250 Hz for ECG and 28 Hz for respiration and the resolution is 16 bits for both. A inertial-measurement sensor with 3-axis accelerometer, 3-axis gyroscope, and 3-axis magnetometer is used to monitor the motion tracking. The sampling rate is 50 Hz and the resolution is 16 bits. Choose by the smart phone or tablet, these sensors can be selected and record the physiological signals individually or collectively. By used of the firmware design, we switch the microcontroller and the bluetooth low energy between the active mode and sleep mode to make the reduction of the power consumption. This work also do with the down sampling of the sampling rate for respiration (250 to 28). It reduce the amount of data, and therefore the BLE can transmit the data faster and go into sleep mode longer. When we adopt the sleep mode, the power consumption of the BLE reduced from 32.2 mW to 6.03 mW. When also using the down sampling and down resolution, the power consumption of the BLE reduced to 2.93 mW, which is only 48.6% of the original version with sleep mode and 9% of the original version without sleep mode. For the 9-axis sensor, the power consumption of the BLE reduced from 31.63 mW to 4.26 mW, which is only 13.5 % of the version without sleep mode. A 300 mAh battery can make device continuously recording and transmitting data for at least 43 hours. The power consumption for the ECG and respiration sensor is about 9.93 mW under 3.3 V operation voltage, and the power consumption is 22.54 mW for 9-axis sensor. It can reduce maximum 29.27 mW on BLE after this work on the BLE.