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Optimal Buzz

Harvard John A. Paulson School of Engineering and Applied Sciences

ES 52: The Joy of Electronics Spring 2018

Engineering the Breathalyzer

 
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System Breakdown

As common inebriation tests simply measure alcohol content on the breath, we designed a dual-system (breathalyzer and reaction game) alcohol intoxication measurement device. I was responsible for the design and build of the breathalyzer, which began with the block diagram shown on the left.

 

Electrical Schematic

In translating the block diagram to schematic:

  1. To simulate different alcohol concentrations and one’s tolerance to alcohol, two potentiometers were used for easy adjustable resistance. Comparisons were made via a differential amplifier circuit.

  2. The comparator helps to reset the shift register counter, allowing for continuous use of the breathalyzer circuit.

  3. A shift register relays the stimulated alcoholic input to the LED Display output by storing and interpreting binary values.

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4. The LEDs’ increase in brightness display linearly correlates to levels of inebriation tolerance and toxicity.

5. Implementing the Synchronous Counter and Integrator allowed for the shift register and LED Display to clear, thus allowing for continuous trials of the breathalyzer to be completed.

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Testing the Final Product

The saw-tooth wave (channel 3) shows the integrator’s slope increasing to 5V and resetting on the falling edge of the comparator’s output (channel 2) and rising edge of the analog switch (channel 1), as the cycle restarts again. The LM555 timer (channel 4) has a 10 mSec pulse from rising to rising edge, which is the time specification allowing the breathalyzer to properly reset.