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The system we are designing will test an individual`s blood alcohol level by analyzing the breath exhaled into our system, in which the sytem will decide whether to let the individual start the car. We will be using an "Ensure" made by "Alcohol Countermeasures" to measure the blood alcohol level. We will also be including a numeric touch pad (state machine) that will replace the existing key ignition system. The driver of the car will have to key in their pin number instead of using a key. The the driver will then be signaled to breathe into our modified breath analyzer. If the driver passes the test he/she may start the car by pressing a start button that will control the starter for the vehicle.
The objective of this design is to help keep drunk drivers off the road. The system will be designed so that it will be able to interface with all current ignition systems. Our system will also eliminate the use of keys to start the vehicle, therefore eliminating the need for keys. The user of the system will be given audio feedback at each stage (ie. whether they passed the keypad test and then the blood alcohol test). This will be done by integrating standard voice chips into the system. These could be replaced by LED`s to control the cost for future designs.
BACKGROUND
Breath Alcohol Tester
The breath alcohol tester is an electronic device used to test the blood alcohol content (BAC) in a person`s blood stream. Several other methods of alcohol detection exist, such as chemical reactions, optical- interference, infrared absorption, and heat generation from a catalytic reaction on a hot platinum wire. These methods, however, have the disadvantages of being difficult to handle and maintain. They are also very expensive and have a very limited lifetime.
This device utilizes a semiconductor sensor to analyze a person`s exhaled breath. This method is both simple and affordable. The semiconductor device offers the an added advantage in that it is robust; it is highly immune to shock and vibration, and therefore more reliable.
The Sensor
The sensor consists of a semiconductor material mounted on a ceramic tube; it is protected by a double layer of 100-mesh-per-inch stainless steel screening. When the alcohol tester is turned on, the sensor is heated to normal operating temperature. During this process, oxygen is absorbed into the semiconductor surface. This causes a depletion region to form betw1een the surface and the body of the sensor. In turn, this increases the resistance of the sensor.
When an intoxicated person blows on the sensor, the alcohol is absorbed into the semiconductor surface and reacts with the oxygen that is already there. This decreases the sensor`s overall resistance in proportion to the alcohol concentration.