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Introduction |
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Results |
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Conclusions |
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Appendices |
In
Retrospect…
(Or: What we wish we had done differently, assuming that it took no additional
time, money, mechanical competence or effort)
The first thing that really boiled our asparagus was our mechanical design. Our design needs two main things: a chamber in which the user’s breath sample can stabilize, and a method of preventing saliva from accumulating within said chamber. As lowly aspiring electrical engineers, we didn’t know jack shoot about mechanical design, so we only semi-succeeded on both counts.
Our pressure chamber, which consists of a largish party balloon, mostly holds the breath sample pretty well, but there’s some inevitable leakage at all straw joints and the holes through which the sensors’ leads poke. There are three straw joints (mouthpiece to pressure balloon, and two between the pressure balloon and the ETOH balloon), and eight holes through which leads poke (four for the pressure sensor and four for the ETOH sensor). Of course, we need some pressure leakage (we don’t want the user to actually blow up the balloon and stress all of our flimsy mechanical parts), but we’d prefer if it were under our exclusive control; breath leaking out through sensor holes may throw off the sensors’ readings.
We didn’t realize that it was necessary to prevent saliva accumulation until very late in the game, after we noticed that (WARNING: the rest of this sentence contains a graphic description of bodily fluids) spit was bubbling out the sensor lead holes and contaminating the leads. We elected to use a ripped up shirt as our Saliva Shield, which seems to work as measured by the reduced volume of spit leaking out of the balloons. But we were unable to eliminate the saliva factor entirely, which means we have to periodically clean the ETOH sensor. Of course, had we more time, etc., we would implement a magical Super Saliva Shield that would block all saliva from entering the Breath-o-Matic.
Another thing that we found somewhat lacking in our design was the method in which code was written and the circuit built. Our design process consisted of testing each component on a white board with a snippet of code to ensure that it worked; after testing the component, we added giant, vaguely related blocks of code to our final C file. We had written most of the code (~700 lines worth) without testing it, and we also built the complete circuit on a solderboard without testing it. Then we crammed the two together, and as is predictable, they didn’t work. Debugging took nearly a week. We could have saved ourselves a lot of pain, frustration, stomach churning and nose running if we had built and tested discrete portions of the circuit on the solderboard, eventually building up to the completed thing. “Oops,” is our feeling on this particular topic.
We sampled the TGS 2620 from Figaro Electronics, and we sampled two Mega32s from Atmel distributors for our project. One Mega32 fell out of our solderboard somewhere, never to be seen again. We killed another one with static death discharge. Finally, we got a working processor from the lab, which is the one that is currently in the Breath-o-Matic. In the spirit of this “In Retrospect” section, we kinda wish that we were able to use at least one of our original samples, which would have allowed this report to paint us as being somewhat more competent.
We also, given the opportunity,
wouldn’t have broken our pressure sensor.
Ethical
Considerations
(Or: Ethics? We don’t need no steenkin’ ethics)
As regarding the IEEE code
of ethics…
1. to accept responsibility in making engineering decisions consistent
with the safety, health and welfare of the public, and to disclose promptly
factors that might endanger the public or the environment.
As we discuss in this section, there are two concerns with our project
that may, under the right circumstances, prove to be a danger
to the public. We have disclosed these concerns fully, and we accept responsibility
for any injuries incurred from our device as long as the device is used
in a safe and responsible fashion, in accordance to
all manufacturer’s guidelines, which include, but are not
limited to:
• Use separate mouthpieces for each person
• Only blow into the mouthpiece of the Breath-o-Matic; under NO
circumstances inhale through the mouthpiece
• Do not use the Breath-o-Matic while excessively intoxicated
• Do not subject oneself to excessive intoxication for any reason
whatsoever relating to the Breath-o-Matic
• Do not open the Breath-o-Matic’s container, except to replace
the battery
• Do not modify the Breath-o-Matic
• Do not use the Breath-o-Matic with any other devices or appliances
• Do not subject the Breath-o-Matic to excessive liquid, heat, vibration
or pressure
2. to be honest and realistic
in stating claims or estimates based on available data
Although we have attempted to calibrate the Breath-o-Matic to the reasonable
extent of our abilities, our methods are intrinsically imperfect. As we
mention in the introduction of this report, we, the designers and manufacturers
of the Breath-o-Matic, make no claims about the Breath-o-Matic’s
ability to detect “legal BAC limits” for the purposes of driving,
operating heavy machinery, or any other potentially dangerous operation.
The Breath-o-Matic should absolutely not be used for this purpose.
In addition, we believe that a BAC of 0.00 is the only safe level for
driving, and related actions.
6. to maintain and improve
our technical competence and to undertake technological tasks for others
only if qualified by training or experience, or after full disclosure
of pertinent limitations
Although we do not claim to be experts at measuring blood alcohol content
we do admit this fact openly. We are, however, familiar with alcohol’s
effects and, as such, feel that we have sufficient perspective to design
this breath alcohol tester. We acknowledge the fact that we do not have
a rigorous or definite method of calibrating the Breath-o-Matic, and to
that end, we do not consider it to be a precision instrument. However,
we were willing to learn quite a few things about BAC levels and their
effects, in addition to a variety of circuit design considerations while
designing and manufacturing the Breath-o-Matic. In this manner, we have
improved our technical competence.
7. to seek, accept, and
offer honest criticism of technical work, to acknowledge and correct errors,
and to credit properly the contributions of others
We were very happy to accept criticism during the course of our project
design, and we were constantly correcting errors during testing (the “forgetting
to divide by a million” bug comes to mind). We’d like to thank
Professor Land for all of his help, guidance, and concerned looks when
we knocked things over. We’d also like to thank John Lee for helping
us decide on speaker noises, and Dave for constantly coming around with
a glazed look in his eyes, asking if we needed a test subject, and all
the other TA’s and consultants and colleagues and yak yak yak, etc..
We also thank Figaro Engineering and Atmel for sampling us the TGS 2620
ethanol sensor and Mega32s, respectively.
8. to treat fairly all
persons regardless of such factors as race, religion, gender, disability,
age, or national origin
BAC measurements are universal across race, religion, gender, disability,
age and national origin. Additionally, our multiple feedback methods,
including auditory and visual, allow persons with various sensory disabilities
to enjoy our product (note that said disabilities may be the result of
alcohol ingestion). Unfortunately, people who don’t have any lung
capacity are out of luck in terms of using our product; we cannot compute
a BAC if we do not have a sufficient breath sample.
Alex tested and and soldered components onto the final solderboard, wrote the keyboard code, helped to test the ETOH sensor and designed the web site. Dan did preliminary design, spoke to parts distributors to get samples, tested and soldered components, built the mechanical structure, performed final ETOH testing, wrote the rest of the code and wrote the writeup.
The Breath-o-Matic is an easy to use, semi-accurate, enjoyable little device, contained in a small (relative to Michigan) little package for Your Convenience. We find it to be informative and fun, and we plan on taking it everywhere we go - just in case. If we had a million trillion dollars, we would buy the world a Breath-o-Matic. Because Lord Knows - it needs it.