Research And Design Of Multi-channel Automated Blood Culture System Based On CAN Bus

In recent years,the incidence rate of all kinds of infectious disease rise significantly.Among of these diseases,bloodstream infection is the most serious one.Blood culture is an important way of clinical diagnosis for Sepsis.The full-automatic blood culture instrument can test if there is bacterium in the blood specimens rapidly and accurately,which is high of application value for early diagnosis for pathogenic bacteria of bloodstream infection,as well as for rational use of antibiotics and decreasing the death risk rate of the patient.At present,the full-automatic blood culture instrument is used only in small number of large hospitals,and mainly is produced by foreign countries.The equipment and consumables are quite expensive.Thus,to design full-automatic blood culture instrument with independent intellectual property,is of great significance for reducing medical cost and economic burden of patients.It will also be of great significant for promoting the blood culture instrument to be popularized and encouraging the development of Chinese national industry in medical apparatus and instruments area.The full-automatic blood culture instrument which based on CAN bus and use STM32F107VCT6 as its control core is of high sensitivity,quick response and exact identification.On the basis of research in CAN bus technique and design of the slave part of a full-automatic blood culture instrument with multiple channels based on CAN bus,this paper will focus on the following five parts:(1)Design a Piezoelectric Quartz Crystal Piezoelectric Sensor based on research of Quartz Crystal Resonator theory,Quartz Crystal frequency modulation principle and Crystal oscillation circuit composed of quartz crystal.The signal frequency of this sensor is responsive to the solution of electric parameter changes.The growth of bacteria in culture medium solution will cause the change of the electric parameter of the solution.It can test if the blood is infected through the signal frequency response.(2)Research the CAN bus protocol and design the CAN bus network node of blood culture instrument.By implementation of distributed control base on CAN bus,2 of CAN node will get the Quartz Crystal Piezoelectric sensor signal from each channel.It will not only shorten the scan period of sensor Channel and also will be expanded easily.It will not influence the scanning speed.(3)Design the timeshare strobe circuit of the sensor channel and the signal conversion circuit.The relay strobe sensor channel control by 4-16 line decoder;using a voltage comparator the AD8611 transform the sensor signal waveform.(4)Study the frequency measurement method.Counts pulses of the converted signal by STM32F107VCT6 timer,we can obtained the frequency of the signal by calculating.(5)Research temperature control method and design temperature control circuitry.Acquire environment real-time temperature using DS18B20 and Achieve temperature control using a improved switching control method.