Breathalyzer Enabled Ignition Switch

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Breathalyzer Enabled Ignition Switch

• ECE 345 Senior Design
• Todd Borrowman
• Robert Wilson

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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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Understanding the TGS2620 Ethanol Sensor

• SnO2 Semiconductor
• Ethanol (C2H5OH) is detected by

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Simple Calibration Circuit

• RS Ethanol concentration dependent resistor
• VC VH 5V dc
• RH 83O
• RL 4kO
• VRL Measured output voltage input to
  micro-controller

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Ethanol Response

• Increased concentration results in decreased
  sensor resistance, RS, and increased load
  voltage, VRL

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Variables to Consider

• Humidity and temperature of environment
• Time-delayed response to reach steady-state

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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 BACs .02, .04, .06, .08, .10,
  .12, and .20

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Calibration Continued
Concentration of Alcohol in Breath (grams/liter) B.A.C. ( limits)
0 0.00
9.5 x 10-6 0.02
1.9 x 10-5 0.04
2.8 x 10-5 0.06
3.8 x 10-5 0.08 (illegal to drive in most states)
4.7 x 10-5 0.10 (illegal to drive in all states)
5.7 x 10-5 0.12
9.5 x 10-5 0.20

• Flasks containing these mock-BACs were created
• Repetitive measurements were performed to find an
  accurate linear calibration equation

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Calibration Achieved
Input BAC Mixtures Average Sensor Voltage Output (VRL)
0.00 .6 V
0.02 4.02 V
0.04 4.14 V
0.06 4.25 V
0.08 4.32 V
0.10 4.42 V
0.12 4.61 V
0.20 (saturated at) 4.75 V
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The A/D Ratio in the BasicX

• 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

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Breathalyzer Circuit
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Program Flowchart
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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

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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

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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

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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

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In Car Circuit
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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

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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

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Questions?