Detection Of ETCO₂ Based On Zigbee Technology

End-expiratory carbon dioxide(ETC02)has become an important tool for intensive care,casualty transport and other medical applications in the medical field.ETCO2 has been listed by the American Association of Anesthesiologists(ASA)as one of the routine surveillance programs in 2005.It is widely used in intensive care,emergency medicine and telemedicine.Because of its noninvasive and continuous characteristics,ETCO2 has been widely used in medical clinic.However,ETCO2 is susceptible to external environment(temperature,humidity,atmospheric pressure)in the detection.Therefore,it has great research prospects to improve the performance of the breathing carbon dioxide monito-ring system.A chemical gas sensor to detect C02 concentration is used in the ETCO2 detection system studied in this paper.The principle of the sensor is based on crystal size effect and uses the change of metal oxide sensor material conductance to detect C02 concentration.In this paper,CSS811 model,a CO2 sensor,is used as the core chip,HDC1080 model,a temperature and humidity sensor,BMP280 model,a pressure sensor are used in the peripheral circuits in the detecting system.This intelligent detection system has finished the measurement of the CO2 concentration,temperature,humidity,gas pressure and the calibration of the concentration of CO2 temperature,humidity,gas pressure.The ZigBee wireless transmission system introduced in his paper is built with CC2530 chips,and a star network is used to build a wireless transmitted network.The hardware circuit is built with STM32F103ZET6 chip,and voltage stabilization circuit,level conversion circuit,communication circuit,and et al.The software design is divided in two parts,the upper computer software design and the lower computer software design.The upper computer software is written by the LabVIEW software,and the man-machine interface is designed to realize the functions of data communication,data processing,data storage and data display.I2C serial communication protocol and ZigBee communication protocol are compiled.The data transmission of ZigBee wireless network is realized by using the serial port transmission function of Z-Stack.The software programming code of the function realization is described.Data reception and storage of the Carbon dioxide concentration,temperature,humidity and gas pressure are realized by I2C bus transmission.In order to improve the accuracy of ETCO2 measurement,a calibration model of temperature,humidity and gas pressure on the concentration of carbon dioxide measurement was established,and the measured data were processed.The calibration model is established with simulation data,and the calibration model is validated with validation data.It is proved that the calibration model can improve ETCO2 measurement accuracy.