The Design Of Low-Frequency Portable Bioelectrical Impedance Detector

Bioelectrical Impedance(Electrical Bioimpedance)technology,is also called bio-impedance(Bioimpedance)or impedance(Impedance)technology simply.It can effectively detect the physiological and pathological information of biological tissues,organs and cells,etc,therefore it plays a very important role in the field of medical diagnosis and scientific research and so on,for example the applications of electrical impedance tomography,impedance flow diagram and bioelectrical impedance analysis of body composition in the medical.Currently,the bio-impedance has not only a wide range of the field of medical applications,but also becomes an increasingly widespread in the agricultural sector,for example the relations' research of beef tenderness with its impedance,the nondestructive testing of quality of fruit and vegetable,impedance determining the freshness of fish and so on.However,currently available bioelectrical impedance measurement instruments have generally higher prices,such as upscale Agilent 4395A impedance analyzer's price is about 400,000 yuan,and ordinary AT2816B of Changzhou Amber Precision Instrument Co.has around 7,000 yuan.And these instruments in the market have the defects of no direction,larger,smaller output current range and so on.Therefore,this paper presents the design of a low-frequency portable bioelectrical impedance detector.The system uses Microchip's PIC16F887 as the core controller,which is embedded A/D converter,and it has no external crystal oscillator circuit and reset circuit and simplify the circuit.The desired signal source of systems is produced by direct digital frequency synthesizer technology(DDS)based on the AD9850 chip,and it becomes the current signal through voltage-controlled current source as the excitation source.The information of amplitude and phase of bioelectrical impedance is measured by the high-performance AD8302 chip detecting amplitude and phase,and is displayed on the LCD screen of YAOXY12864B.The drive code of entire system is performed to write and debug in the integrated development environment of MPLAB IDE v8.88.Now,the design of the entire system's hardware and software is completed.