In the early 1970's my brother Chris experimented with several similar sensors manufactured by the Figaro Engineering Company in Japan. He found the sensors could detect various chemicals but didn't offer enough sensitivity or selectivity to alcohol in the presence of other chemicals to yield a quantitative result. I bet the same holds true for the sensor in this project. The data sheet for a similar sensor (MQ-3 from Hanwei Electronics) shows a predominate response from ethanol, closely matched by the responses to methane, propane, and hexane. Also, response varies with respect to relative humidity.
So, the project might offer a qualitative measure of alcohol, but I wouldn't trust it to detect alcohol well enough to avoid a drunken-driving arrest. It's best to not drink and drive. So, treat this project as a novelty to share with friends.
Also, breathalyzers use a fuel-cell arrangement in which the oxidation of alcohol at a platinum electrode produces a current than the instrument can convert to a parts-per-million or other value. The platinum-based sensors can last for a long time, but the semiconductor sensors last only for a year or two. Perhaps micro-engineering technologies will one day yield a surface that produces a selective response for ethanol. That type of sensor would not react to other chemicals.
I think you have a point, Absalom. But I think it may be because this device -- while valid and perhaps accurate -- would not meet the criteria for devices used by law enforcement. Even so, it this device discouraged a drunk from driving, it provides a real service.
Hey Jon, you are absolutely correct, semiconductor based alcohol sensors are not accurate as one may think. As such, this project is marketed and should be used as a novelty device only. I purposely stayed away from adding a specific Blood Alcohol Content (BAC) reading to the app for this very reason. There was recently an independent study done on the accuracy of consumer semi-conductor based breathalyzers here, it's quite interesting.
How about *not* drinking before you must drive? I am always amazed that people try to find how close they can get to breaking the law and putting others in danger before actually murdering someone. I don't see the value in that behavior.
Cvanderwater, that an ideal situation and more preferable. But due to some common commitments and business networking we may force for a sip in parties. I mean unavoidable circumstances, otherwise we are very cautious about it.
I guess "unavoidable" is a matter of opinion, unless someone is putting a firearm to your head to force you to drink... I will gladly take a beer if I am traveling by bus or bicycle, but when I have to drive then even if every one of my colleagues is drinking alcohol, I will still order a non-alcoholic beverage.
My simple reasoning is: I don't want to be able to say to myself "it would have been different if I had not been drinking" in case something would go wrong. So, I don't drink when I know I still need to drive, or I make sure I don't need to drive. It is very simple actually.
Thanks for the link, Al. that was good thinking to avoid adding a Blood Alcohol Content reading to the app. Very responsible. That could certainly be used to justify what might actually be drunken driving.
You're absolutely right, cvandwater, it actually is very simpl to avoid driving drunk. Yet, somehow, 32% of our annual highway fatalities in the U.S. are caused by drivers over the limit. Seems incredible, but it's true.
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