Design And Research Of Impedance Measurement System Based On STM32

Impedance is an inherent property of every organism,representing the ratio of voltage phasor to current phasor.The purpose of impedance measurement is to study the electrical performance of electronic components or unknown networks.With the rapid development of integrated circuit technology and the emergence of new demands,the related research of electrochemical impedance mainly focuses on the impedance integrated chip,the design and manufacture of impedance electrodes,and the surface modification of impedance electrodes.The main research and results of this paper are as follows:(1)In order to meet the needs of broadband and portable impedance measurement in electrochemical applications,the technical specifications of impedance measurement system were determined,and an impedance measurement scheme combining potentiostat and amplitude and phase identification module was proposed.In this scheme,the amplitude and phase identification module is used instead of the frequency response analyzer,which greatly reduces the volume of the measurement system.At the same time,the analog-to-digital converter with microcontroller can realize the purpose of signal acquisition,and the cost is relatively low.In addition,the scheme can be redeveloped according to the actual situation,and the range of impedance measurement can be flexibly selected.It can be widely used in the electrochemical analysis of biological materials.(2)The hardware design and software compilation of the impedance measurement system are completed.The hardware circuit includes signal generation module,potentiostat module,impedance measurement module,communication module and power module.The software program is divided into three parts: lower computer program,C# interface and Android APP.The lower computer program includes initialization program,DDS control program,impedance measurement program and serial communication program;C# interface consists of serial communication program,measurement window,drawing window and data calculation window;Android APP can be divided into login interface,navigation bar interface,Bluetooth communication program and data display program.(3)The function and index of the impedance measurement system are tested.The ripple,crystal oscillation signal and communication module of lithium battery power supply and USB power supply are measured in hardware circuit.The ripple value of analog power supply is less than 1%,the crystal oscillation is normal,and the data of communication module is normal.In the software part,firstly,the standard impedance is measured with 0.1% resistor and capacitor.The measurement frequency range is 1 Hz-10 MHz,the average error of modulus is less than 3.1%,and the average error of phase is less than 1.766 degrees.Then,the solution impedance is tested with PB buffer.In the frequency range of 100 Hz-1 MHz,the concentration of PB buffer is 0.2 mol/L,0.02 mol/L and 0.002 mol/L,respectively,and the corresponding maximum modulus is measured.The average errors were 4.51%,5.7% and 5.88% respectively.