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Breathalyzer Enabled Ignition Switch

Breathalyzer Enabled Ignition Switch . ECE 345: Senior Design Todd Borrowman Robert Wilson. Overview. Sensor to detect BAC Microcontroller to calculate BAC and compare to state limits Wireless transmitter and receiver to transmit signal from handheld device to relay in ignition circuit.

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Breathalyzer Enabled Ignition Switch

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  1. Breathalyzer Enabled Ignition Switch ECE 345: Senior Design Todd Borrowman Robert Wilson

  2. Overview • Sensor to detect BAC • Microcontroller to calculate BAC and compare to state limits • Wireless transmitter and receiver to transmit signal from handheld device to relay in ignition circuit

  3. Understanding the TGS2620 Ethanol Sensor • SnO2 Semiconductor • Ethanol (C2H5OH) is detected by…

  4. Simple Calibration Circuit • RS = Ethanol concentration dependent resistor • VC = VH = 5V dc • RH = 83Ω • RL = 4kΩ • VRL = Measured output voltage; input to micro-controller

  5. Ethanol Response • Increased concentration results in decreased sensor resistance, RS, and increased load voltage, VRL

  6. Variables to Consider • Humidity and temperature of environment • Time-delayed response to reach steady-state

  7. On to Calibration… • Blood Alcohol Concentration, or BAC, is the amount (in grams) of alcohol per 100mL of blood • Alcohol concentration in the breath (g/210L) is proportional to the BAC by a factor of 2100 • Want to create test solutions representative of the following BAC’s: .02, .04, .06, .08, .10, .12, and .20

  8. Calibration Continued… • Flasks containing these mock-BAC’s were created • Repetitive measurements were performed to find an accurate linear calibration equation

  9. Calibration Achieved

  10. Voltages were applied to A/D pin of BasicX The digital outputs were recorded Correlation found between analog voltage and digital value to be about .2024 The A/D Ratio in the BasicX

  11. Breathalyzer Circuit

  12. Program Flowchart

  13. Analog to Digital conversion • Built in to Basic X microcontroller • Reads voltage output from the sensor circuit continuously until a maximum value is reached • Program converts maximum value to BAC equivalent

  14. Display • Implemented display using a 5X7 red LED array • Allows two-digit display using 12 outputs from the Basic X • Unfortunately the small array size prohibited differentiation of similar letters e.g. M and N, U and W

  15. State Select Button • Allows different state limits to be selected • Colorado, Delaware, Minnesota, and Pennsylvania have a legal limit of 0.10 BAC as opposed to the other states which have 0.08 as the legal limit • Pushing the button once displays the selected state, pressing repeatedly cycles through the states

  16. Linx Chips • Ready-made transmitter and receiver chips • Operate at 903.37 MHz • Sends signal from the Basic X on hand-held device to car circuit

  17. In Car Circuit

  18. Automobile Ignition Circuit • Output from receiver closes relay on ignition circuit allowing the operation of the vehicle • Relay is normally open and only closes when excited by receiver • In demonstration relay was represented by LED indicator

  19. Improvements • Fuel cell sensor to replace semiconductor • Complete linear response • No time delays • Fewer variables • More efficient algorithm to obtain accurate BAC on first attempt • Larger display • Improves clarity • Three-decimal precision

  20. Questions?

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