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Introduction
Automobile Breathalyzer
This topic was selected partially because it involves a bioengineering sensor, but primarily because it provides an easily demonstrable and extremely relevant application to the general public.
Objectives
1998, the last year for which statistics are available from the National Highway Traffic Safety Administration, brought 15,953 alcohol-related traffic fatalities. This figure does not even begin to reflect the number of people who were injured, both physically and psychologically, by these incidents. Methods for curbing drunk driving include revoking offenders’ licenses and enrolling them in substance abuse rehabilitation programs. Disabling a vehicle’s engine, however, precludes the possibility of such incidents altogether. If a Breath Alcohol Test indicates that a driver exceeds Illinois’s 0.08% Blood Alcohol Content (BAC) limit, the Automobile Breathalyzer will disable a car’s ignition.
Benefits
 Determines whether or not a user is legally in a condition to drive
 Protects the user, the general public, and property from injury, thus saving both lives and money
Features
 Indicates “Pass,” “Fail,” and “Warning” states of intoxication
 Disables the ignition if a user exceeds 0.08% BAC
Block Descriptions
the Alcohol Source consists of either a genuine or, for safety and for testing purposes, a simulation of a user’s breath. This sample is input directly into the Alcohol Level Indicator.
The Alcohol Level Indicator determines and displays the Alcohol Source’s BAC. Using a method appropriate for the device ultimately purchased, the electrical representation of this result (e.g., voltage) is fed into the Signal Processor for further analysis.
The Signal Processor includes possibly basic amplifiers to augment the output signal from the Alcohol Level Indicator and a microcontroller to regulate access to the ignition and to trigger appropriate messages to the user.
Based on outputs from the microcontroller, LEDs on the Message Console indicate such conditions as “Pass,” “Fail,” and “Warning.”
Coupled to the Signal Processor possibly by a transformer, the Ignition starts if the user’s BAC is acceptable. For demonstration purposes, this block is an appropriate model (e.g., alternator), not a complete vehicle ignition.
Performance Requirement
Assuming results from the Alcohol Level Indicator are accurate and depending on the resolution of that device, the system should function properly within 0.001% BAC.
Verification
Testing Procedures
Proper operation will be verified for simulated BACs ranging from 0.00% to .10%. The system should correctly enable or disable the Ignition block and display appropriate messages.
Tolerance Analysis
In order for the Message Console to work as specified, the output from the Signal Processor block must be 5 V 20%.