Design Of Three-electrode Blood Alcohol Concentration Detector

Blood alcohol concentration (BAC) has been widely used in judgment of traffic accident which caused by drunk and adopted by traffic police department. The equipment of detection for BAC is gas chromatograph. It is so expensive and time consuming and bulky that not suitable for field testing.At present, there are some problems such as low accuracy and impacted by environmental factors in Breath alcohol testing instrument. Therefore, it is practical significant to design a field blood alcohol concentration tester which can improve the level of determine the accuracy and effectiveness of driving accidents by drunk. It was prensent to design a portable blood alcohol concentration tester based on three-electrode sensor.The working principle of tester is based on the linear relationship between the values of the test current and blood alcohol concentration. By measuring the current, and then the blood alcohol concentration is calculated. An enzyme three-electrode sensor was adopted in this tester.Three electrodes are composed by counter electrode, working electrode and reference electrode. When a constant voltage was applied between reference electrode and working electrode, a current would be generated between working electrode and the counter electrode.Hence constant potential circuit and micro-current measurement circuit are needed on hardware circuit.The core device is high precision instrument amplifier, which uses the depth of the negative feedback voltage to achieve a stable voltage.The micro-current voltage is measured by converted to a voltage.The tester adopts the STM32microcontroller as the main chip to achieve the goals of low power consumption and high reliability.In software design, it was based on μc/OS-Ⅱ.First μc/OS-Ⅱ operating system was transplanted to STM32microcontroller, and then multi-tasking software’was designed based onμc/OS-Ⅱ. Multi-tasks are composed by DA converter control task, AD sampling task, display tasks and other tasks. DA converter control task can manipulate DA converter generating different waveform. AD sampling tasks sample convered current and calculated the concentration, then the concentration was pass over to display task. The display task drive screen to display the concentration.The results show that the error of potentiostat circuit is less than lmv and the stable voltage range is between-3.3V to3.3V. The micro-current test circuit can measure the limit current reached0.01μA. The tester can detect blood alcohol concentration from1.00to10.OOmmol/L accurately.