Mq-3 Alcohol Sensor power

Projects General Guidance
1

I have coded and been prototyping multiple "breathalyzers" based on the MQ-3 alcohol sensor. AFTER I had begun to build my prototypes did I learn of a "drinkduino" shield that already exists using the same sensor (I believe).

There really isnt too much (or at least as much as I would expect) out there on this sensor.

Based on the MQ-3 data sheet the MQ-3 uses no more then 750mw of power. This is clearly too much for an Arduino pin to power.

In building my design and prototypes I included the venerable LM7808 5v regulator to power essentially the whole project including the Arduino Nano (in an attempt to keep both size and power usage down). Looking at pictures of the "Drinkduino" (which is a shield as I mentioned) there does not seem to be any type of voltage regulation. Also being a shield it would appear to be powered totally by the Arduino.

Having to obviously want to make my project (breathalyzer) mobile/ battery powered the LM7808 becomes a bit of a nuisance in the sense that it need a min of 7v in order to properly regulate everything to 5v.

My question is two fold.

#1 Is there anyone out there that has had direct contact with the "Drinkduino" shield that can comment on how the MQ-3 gets its power for the heater element?

#2 Can anyone suggest a potentially better way to power/regulate this project? I could not find any 6AA bat holders locally so I have currently procured a few 8AA (12v) bat holders. The holder and batts are MUCH larger then my project as a whole.

Compound the battery dilemma with the fact that running 12v (8AA) at what? 2000mah? totally causes my LM7808 to get HOT!!!

We all know that heat = lost energy and I just don't like that. I'm sure it would run a little better at 9v (6AA) but again I had a hell of a time finding any locally. Even thought Radio Shack says that they stock them in their stores.

I consider myself a novice and call upon the infinite wisdom of the Ardunio.cc veteran (or not) forum board members.

Thank you!

MQ-3 Datasheet via Sparkfun http://www.sparkfun.com/datasheets/Sensors/MQ-3.pdf

2

750 mW at 5V is 150 mA which is not too bad. To much to drive with an Arduino output pin but if the heater is drawing most of the power you should be able to drive it off the 5V power pin.

3

Indeed the heater element is the power hog in the scenario. Aside from the heater the sensor acts very much like a variable resistor (based on alcohol). The heater element essentially is there to vaporize your breath.

Thank you for the keen advice I will prototype this up and test ASAP. I only wonder why the few demos and docs I had read on project like this had not done it this way.

I am going to assume your idea will work as I would be willing to bet that this is how the "Drinkduino" I referenced earlier is powered.

Anyone have any other sound advice?