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Alcohol breath sensor

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TheMerovingian

Wed Apr 19 2006, 10:16PM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

I found, in the place i usually buy my components, some little neat alcohol sensors. The datasheet is present but is a bit scarce of information regarding the way it is meant to be wired and calibrated. It needs 5V filament heating plus 5V for the sensor part and a load resistor for the response. Probably the response is a voltage but no sensitivities are shown. I want to wire one that way, buffer the output with an opamp and then measure it with a panel meter possibly calibrating the sensitivity to obtain 1mV = 1ppm. It's not easy to obtain an alcohol vapour with a know concentration but is possibile (it is possible to calculate the partial pressure of etanol in an hydroalcolyc solution kept at const temperature, in a closed container). Alternatively i would use a scale from 0 to 100mV calibrating on phisioligical response (aka on a drunk friend) to have a semi-quantitative scale (goodbye to repeteability .....

). Anyway it is more for learning and fun than for a specific reason that i want to build an alcool breath tester

...

Wed Apr 19 2006, 10:42PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Couldn't you get a reading by drinking a measured amount of the drink, then divide by the mass of water in your body, then making the display read that?

Interisting project... Probably a classic example of I could have bought for $15 but you ended up spending $50 and a few hours of you timet to get a device that is less accurate/bigger/etc

McFluffin

Thu Apr 20 2006, 02:09AM

Registered Member #119 Joined: Fri Feb 10 2006, 06:26AM
Location: USA
Posts: 114

Hey! Its not the cost, everyone knows that the 5 hours we spend looking for a broken microwave could probably buy us several if we were working.
Anyway, as far as calibrating, have you tried immersing the sensor in alcohol? Is this possible? Not really sure what sort of sensor this is, but it might give you some sort of extreme value if you can. Or, put it right over some ethanol. I'd be curious to put this over methonal or isoproponal and see what you get as well.

Desmogod

Thu Apr 20 2006, 02:10AM

Registered Member #139 Joined: Sat Feb 11 2006, 11:01AM
Location: Perth, Western Australia
Posts: 358

... wrote ...

Couldn't you get a reading by drinking a measured amount of the drink, then divide by the mass of water in your body, then making the display read that?

Nope, there are too many variables. Without suitable info on the datasheet, the only way to calibrate would be alongside a "real" breathalyser. Just don't get drunk, jump in the car and go and find one.
"But orifisher, I jusht need to cla-hic-cal-hic-calalibrate my project"

Superkuh

Thu Apr 20 2006, 03:20AM

Registered Member #59 Joined: Thu Feb 09 2006, 05:45AM
Location: Wisconsin, USA
Posts: 12

I know this only tangentially related to what you have asks for, but I would look for ideas here: Breath-o-Matic alcohol sensor

It is a well documented AVR based microcontroller design final project that uses a similar sensor to yours. They have various ideas for the mechanical sampling design you might use, or a thorough plan of action if you have experience with AVR microcontrollers.

Electroholic

Thu Apr 20 2006, 05:06AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

Sounds like a fun project!
I remember doing partical pressure in chem...
I guess you can make a 1L plexi box, then vaporize a known amount of ethanol...
nah, i have no idea what i am talking about...
Keep us updated tho! I love projects!

TheMerovingian

Thu Apr 20 2006, 09:15AM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

that's i want to do to calibrate it.

At given temperature i can calculate tha partial pressure of alcohol and water, hence the composition of vapour. Another method can be getting rid of the panel meter and using a logaritmic bargraph instead setting the last leds on a drunk person. IT would be fun measuring alcohol concentration in Drunk Units (oh man you have 10 drunk units

). THe problem is that peoples don't respond in the same way to alcohol, many methabolize slowly, others very quickly, maybe i can calibrate the device on them. It would be impossible for me to reach their alcohol concentration without dying..... (oh man, the sensor tells me that i'm dead

)

It would be a classical boring weekend project, with low cost and lots of fun ^^

Simon

Fri Apr 21 2006, 01:47AM

Registered Member #32 Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549

The concentration of alcohol in the breath is supposed to be directly related to the concentration of alcohol in the blood. So while larger people will need more alcohol to get a given BAC, that won't throw your tester. It still needs personalised calibration to be properly accurate.

For anyone who's interested, Jaycar in Australia also sells alcohol sensors (as well as a few other gas/vapour sensors).

TheMerovingian

Fri Apr 21 2006, 10:02AM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

I found them on futurlec., they cost 7.9dollars each
along with other sensors present in the store

Bored Chemist

Sat Apr 22 2006, 10:36AM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

To a good aproximation you, after a few drinks, are a solution of alcohol in water at 37C.
You can use that sort of solution to calibrate the machine.
Here in the UK the limit is (IIRC) 80 mg/ 100 ml so you could make a solution of that concentration in water by diluting vodka or some such, warm it to 37C then blow air through it and onto the sensor. That should give you a fairly good calibration point.

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