Picture of Arduino Breathalyzer

What is a breathalyzer you may ask? It is a device for estimating blood alcohol content (BAC) from a breath sample.In simple terms it is a device to test weather a person is drunk or not. As the title suggests it runs on the arduino.Our breathalyzer uses the MQ-3 alcohol sensor from sparkfun.It is a simple and fun to do project.

This instructable explains how to create your own breathalyzer , making a shield for the arduino , putting the breathalyzer in a box, and making some changes to your breathalyzer.

This Breathalyzer is not meant to be used as a means of breathalyzing. The MQ-3 is not accurate enough to register exact BAC and is sensitive to temperature and humidity.Never drink and drive and if you do call me =D .

Remove these adsRemove these ads by Signing Up

Step 1: Parts & Tools

Picture of Parts & Tools


~ Arduino Uno -

~ MQ-3 Alcohol Sensor -

~ 100k Ohm Potentiometer -

~ 330 Ohm Resistor -

~ 5 x Green LED's -

~ 3 x Yellow LED's - Sparkfun.conm

~ 2 x Red LED's -

~ 7805 Voltage Regulator - Local Electronics Store 

~ 1000 uf Capacitor - Local Electronics Store

~ 2 x 9v Batteries - Local Electronics Store


~ Soldering Iron -

~ Solder Wire -

~ Jumper Wires

~ Protoboard -

~ Project Box - Local Electronics Store

~ Inhaler Tube - I Found It In My House 

Step 2: The Chemistry

Picture of The Chemistry

When the user exhales into a breath analyzer, any ethanol present in their breath is oxidized to acetic acid at the anode:

CH3CH2OH(g) + H2O(l) → CH3CO2H(l) + 4H+(aq) + 4e-

At the cathode, atmospheric oxygen is reduced:

O2(g) + 4H+(aq) + 4e- → 2H2O(l)

The overall reaction is the oxidation of ethanol to acetic acid and water.

CH3CH2OH(l) + O2(g) → CH3COOH(l) + H2O(l)

The electrical current produced by this reaction is measured by a microprocessor, and displayed as an approximation of overall blood alcohol content (BAC) by the Alcosensor.

blackcamo3 months ago

you can get all the parts for a fraction of price..

redinside4 months ago

Hi, I bought LM393-MQ-3 Gas Sensor module. How should I connect this module to Arduino and what kind of conversion and calibration should I do to get the level of BAC and display it on a LCD.

Thank you very much

philbot1 year ago
I have tried this a few times but I can't get anything to work, all of the LEDs turn on immediately and just stay on, any ideas on what I'm doing wrong?
pasteler01 year ago
The code was taken from:

Should at least leave the header...
Bot1398 (author)  pasteler01 year ago
Mentioned the header sorry for not mentioning it before
djoy21 year ago
can put a LCD display on this project and how? could you please help for my project
djoy21 year ago
can i use atmega328 instead?
mattgilbert2 years ago
As pointed out in the comments on this page, Sensor pin B needs to be connected to VCC, not GND. This is what the sample circuit in the datasheet shows, and a student of mine couldn't get the project to work until we did it this way.
nodoubtman2 years ago
Hi! How the MQ-3 SENSOR is hoocked up on the board?

thank you!
Bot1398 (author)  nodoubtman2 years ago
I have attached the schematic on step 5
The ed2 years ago
I wanted to ask, is 6 volts from 4 AA batteries too much for the sensor? Can I use 4.5 volts instead?
Bot1398 (author)  The ed2 years ago
Yes, You should use 4.5 volts instead always be on the safer side
The ed Bot13982 years ago
Thanks a lot. I have since gotten a DC-DC converter and got the 5 volts I needed. But anyways thanks for the reply
nice one what is the cost after shipping to india??
Bot1398 (author)  Pranavthegreat3 years ago
They take 11$ to ship to india but its worth it.
techxpert3 years ago
very nice! i've been looking for a breathalyser for a long time now and this is the cheapest except the arduino uno try this one instead :)