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  • Alcohol Breathalyzer Circuit

  • Created: Dec 10, 2014

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Summary

Alcohol Breathalyzer circuit is a device that determines the blood alcohol content (BAC) of a person. The alcohol content is detected from the breath of the user and displayed in percentage using a three digit seven segment. The device uses SST89E58RDA-40-C-PIE microcontroller, a member of the FlashFlex family of 8-bit microcontroller that has dual block SuperFlash EEPROM with programmable counter array and low EMI mode.


The circuit also uses MQ135 gas sensor. It is a stable and sensitive sensor that can detect ammonia, carbon dioxide, alcohol, smoke, nitrogen dioxide etc. The sensor consists of a tin dioxide sensitive layer inside aluminium oxide micro tubes, measuring electrode and a heating element inside a tubular aluminium casing. The front end of the sensor is covered using a stainless steel net and the rear side holds the connection terminals. The ethyl alcohol present in the breath is oxidized into acetic acid while passing over the heating element. This ethyl alcohol falls on the tin dioxide-sensing layer and as a result its resistance decreases. This resistance variation is converted into a suitable voltage variation using an external load resistor. In addition, the sensor has different resistance values at different temperature and concentration of gases. The manufacturer recommends calibrating the sensor at 100ppm of ammonia or 50ppm of alcohol. Moreover, the recommended value of the load resistor is between 10K and 47K.


Alcohol Breathalyzers are generally portable hand-held device that may be useful for on-site alcohol recognition for students, workers, as well as suspects in roadway accidents where the subject has to blow in the mouthpiece to get the results. It is an appropriate device for random alcohol testing from places of work, industries etc. Thus, the device presents an accurate output that will help other people in effectively monitoring their BACs to maintain a healthy life.