Ethanol breath measuring system

Driving after drinking is considered extremely dangerous and severe limits to alcohol drink before driving are enforced in several countries. This paper describes a simple and cheap device which is capable of estimating the blood ethanol level from the expired breath. The device employs a 3 mm×6 mm gas sensor based on Nb2O5 thin-film which features good sensing performance towards ethanol. A suitable electronic circuit is employed in order to measure the conductivity of the gas sensor and to control its working temperature. The circuit is based on a small microcontroller board (Teensy 3.2) and some additional analog circuitry. Similar devices are already available off-theshelf, however, most of them do not guarantee an accuracy suitable for a quantitative measurement of breath ethanol. The proposed system, instead, has been developed trying to optimize accuracy, power consumption and size. Furthermore, such a system employs a novel gas sensor based on a Nb2O5 sensing film, which has not yet been employed in such a field. The system allows one to set the working temperature of the sensor at its optimal value (350 °C) and to simultaneously measure the sensor resistance in the range between 10 MΩ and approximately 1 GΩ. The quite low power consumption together with the very small size of the system make it very suitable for portable applications such as alcohol drive tests which can warn drivers before starting driving.