Step 5: Build the Circuit

The Circuit is pretty straight forward.To connect the sensor, you have to connect one of the H pin to +5V Supply (use a external power supply) and the other one to Ground.Pin B (any of them) you connect to Ground.And pin A to arduino analog pin0 via 100k ohm potentiometer.To make the LEDs work, I have connected them in sequence using the Digital Pins 2 till 11 (ten LEDs total). Remember to use a resistor between 220Ω and 470Ω for each LED.I soldered the LEDs on a small protoboard and connected one wire to each LED which connected the LEDs to the arduino.To Power the arduino we are going to use a 9v battery and I also soldered a switch so that the breathalyzer can be switched on or off.I used a common switch for the 5v power supply and the arduino power supply.See the Last Image For The Circuit Diagram.

<p>Thanks this is interesting and unusual. </p>
Nice description, I simplified it for prototyping and, I added a wait timer in the code for the mq3 to warm up about 15min.
<p>Why do you need the potentiometer? </p>
<p>hello, i made a cheap Breathalyzer2.0. please check it out</p><p>All credit goes to you.</p><p>Thanks</p><p>https://www.instructables.com/id/Remix-Breathalyzer-20-Alcohol-Meter/</p>
<p>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.</p><p>Thank you very much</p>
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?
The code was taken from: http://www.danielandrade.net/2010/03/07/building-an-breathalyzer-with-mq-3-and-arduino/ <br> <br>Should at least leave the header...
Mentioned the header sorry for not mentioning it before
can put a LCD display on this project and how? could you please help for my project
can i use atmega328 instead?
As pointed out in the comments on <a href="http://www.danielandrade.net/2010/03/07/building-an-breathalyzer-with-mq-3-and-arduino/" rel="nofollow">this page</a>,&nbsp;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.
Hi! How the MQ-3 SENSOR is hoocked up on the board? <br> <br>thank you! <br>marC:)
I have attached the schematic on step 5
I wanted to ask, is 6 volts from 4 AA batteries too much for the sensor? Can I use 4.5 volts instead?
Yes, You should use 4.5 volts instead always be on the safer side
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??
They take 11$ to ship to india but its worth it.
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 :) <br> <br>http://www.dealextreme.com/p/arduino-uno-rev3-development-board-120464?item=15

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