Project #14: Components – SparkFun Alcohol Gas Sensor – MQ-3 – Mk18


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SparkFun Alcohol Gas Sensor – MQ-3

SparkFun Item: SEN-08880

This alcohol sensor is suitable for detecting alcohol concentration on your breath, just like your common breathalyzer. It has a high sensitivity and fast response time. Sensor provides an analog resistive output based on alcohol concentration. The drive circuit is very simple, all it needs is one resistor. A simple interface could be a 0-5V ADC. This sensor has a high sensitivity and fast response time. The sensor’s output is an analog resistance. The drive circuit is very simple; all you need to do is power the heater coil with 5V, add a load resistance, and connect the output to an ADC. This semiconductor gas sensor detects the presence of alcohol gas at concentrations from 0.04 mg/L to 4 mg/L, a range suitable for making a breathalyser. The sensor’s simple analog voltage interface requires only one analog input pin from your microcontroller.

To calculate estimated peak blood alcohol concentration (EBAC), a variation, including drinking period in hours, of the Widmark formula was used. The formula is:

EBAC = ( 0.806 × SD × 1.2 BW × Wt \ MR × DP ) × 10


-0.806 is a constant for body water in the blood (mean 80.6%)
-SD is the number of standard drinks, that being 10 grams of ethanol each
-1.2 is a factor to convert the amount in grams
-BW is a body water constant (0.58 for males and 0.49 for females)
-Wt is body weight (kilogram)
-MR is the metabolism constant (0.015 for males and 0.017 for females)
-DP is the drinking period in hours
-10 converts the result to permillage of alcohol

BAC% = Breath mg/L * 0.21

1 x SparkFun Alcohol Gas Sensor – MQ-3
1 x Pololu Carrier for MQ Gas Sensors
3 x Break Away Headers – Straight
1 x 220k Ohm

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