I have a few questions concerning the [MQ-3 Alcohol Sensor and what it can do.
I want to make a basic breathalyser by interfacing it with an Arduino. I already have a working digital clock project, which basically consist of a housing, the Arduino and a LCD. I plan on just adding the MQ-3 (which I’ll place in a hollowed out microphone) to the clock, wiping the clock program and replacing it with a new one. The idea is to have the user blow into the mic, having the Arduino take the reading, and display it as a numerical value on the LCD which increases with the level of detected alcohol.
This is where I’m a little concerned. Will the MQ-3 take reliable enough readings to be used like this? As in, will it be able to determine a realistic average of the overall alcohol the person has consumed? And will I be able to determine a person’s BAC with the sensor? I think that I’ll have to know their body weight to be able to calculate it, or am I mistaken?](http://www.sparkfun.com/commerce/product_info.php?products_id=8880)
You don’t need to know a person’s weight, measuring Blood Alcohol Content (BAC) can be the “Volume of alcohol per volume of exhaled breath (eg. 0.08 mg/L)” AKA alcohol concentration, which the MQ-3 measures.
You can’t really “blow” into a microphone, you only sniff the person’s breath which might be diluted due to airflow (waving the mike around, singing far away from it etc) and give a low reading. Grabbing the sensor’s peak reading might help. The “pro” breathalyzers also incorporate a pressure sensor to monitor the “blow”, so that it’s from the lungs, mid-breath. The sensor (alcohol+pressure) is at one end of a tube, you blow in the other end of the tube (which has a vent in the middle).
I haven’t used the MQ-3 sensor, people complain its heater must be on for hours (24 hours in the manual) for it to stabilize.
If you Google ‘building a breathalyzer’ you can find many similar projects with an Arduino:
http://sensorworkshop.blogspot.com/2008 … ensor.html
http://www.danielandrade.net/2010/03/07 … d-arduino/
http://www.instructables.com/id/Breatha … icrophone/
Hope this helps.