Respiratory monitoring system using Bluetooth Low Energy

Abstract

The paper presents a system for monitoring respiratory frequency and strength using a BLE transmitter in non-connectable advertising mode and a variable impedance sensor operating in a relaxation oscillator circuit. The presented solution is characterized by low energy consumption. Both the measurement system and teletransmission system operate at 2.2 V power supply. By using a micropower operational amplifier, the analogue part of the system consumes 240–300 μW. Unipolar power supply and configuration of the relaxation oscillator enable to create a pseudobinary signal with the frequency f < 10 kHz. The relaxation oscillator is connected to the microcontroller binary input without having to convert the signal. By using a System On Chip (SoC) with CPU ARM Cortex to control the radio and perform measurements of the pseudobinary signal, the design was simplified and its dimensions were reduced. The operation of the analogue part of the system was compared with a commercial sensor. In addition, the ability of the system to reproduce the breath cycle signal on the BLE side was verified. Differences between the duration of individual cycles turned out to be statistically insignificant, both in the case of normal (p = 0.6889) and fast (p = 0.3226) breathing.