| Car accidents caused a very serious impact on human property and human life. The traffic accidents caused by drunken driving is16times of drunk driving. Therefore, the detection and prevention of drink driving is attracted attention by more and more countries. Now breath alcohol tester and blood type detector are the mainly traffic police detection tools at home and abroad. Breath tester is mainly use the circulation principle of the blood, the testing instrument measure the alcohol concentration by coefficient which set according to the ratio of the alcohol concentration and the air concentration of alcohol. The breath tester had the detection precision problem. Blood type test is the wound detection method, it had the time difference problem. Near infrared is a rapid, accurate and noninvasive detection method, it widely used in the human body material detection, Compared with the former two testing methods detection the near infrared detection has irreplaceable advantages. This paper designed a detection system which detect the driver’s alcohol volume fraction of blood.This paper introduced the light propagation mode in the skin tissue, the interaction with the skin and optical parameters proved pulsation theory can detect the blood alcohol volume fraction use the formulas based on Lambert beer’s law. Determined that optical path correction factor B which influenced by scattering is feasible. In addition selected the fingers front-end that contains abundant micro arterial blood as the test position, Light incident from the back of the fingers is the detecting method.Transmitted optical signal through the TE-InGaAs detector converted into very weak light signals. Therefore, interference with the signal can easily be lost and disturbed in the later process.A blood alcohol detection method was investigated based on NIR (near-infrared) spectroscopy. And a low-noise, low-drift and high-precision preamplifier was designed to detect the blood alcohol volume fraction accurately. In the current-voltage conversion section, the simulation of drift and error of two kinds of circuits were carried out by Multisim software. AD620was selected in the preamplifier part which could improve the CMRR (common mode rejection ratio) of circuits. The results of simulation showed that the current-voltage conversion circuit of symmetrical compensational low-temperature drift can suppressed the drift and reduced error better. Compared with the OP07current-voltage conversion circuit, the error could be reduced by2%, while the draft could be reduced by97%, which could support weak signal analyzing. The system designed a band-pass filter with cutoff frequency range from0.3Hz to10Hz, which mainly used to reduce interference during the detection process. The main amplifier circuit used comparative methods, selected the OP07operational amplifier amplified the signal100times. This met the input requirements of the microcontroller. In addition to its own noise, other outside noise especially the frequency noise may drown valid signal, therefore, a notch filter can be designed in the subsequent circuit part and a narrow-band filter can added to reduce the noise. Further, isolated the overall circuit can effectively reduce the external interference.Finally, the peripheral acquisition circuit was designed based on the new8051STC12C5A60S2/AD/PWM series SCM in the digital circuit part, the new8051STC12C5A60S2/AD/PWM series SCM have high-speed, low-power, super anti-jamming features, and it contains A/D conversion function. Chip-level conversion circuit STC232composed the serial output circuits, the system baud rate is9600bps. |
PDF Full Text Request