Breathalyzer Microphone using an Arduino

Arduino Breathalyzer Microphone (1)

The breathalyzer microphone is a system for the inconscpicuous collection of blood-alcohol content level data sets. In other words, you can measure a person’s sobriety with a device, that for all intents and purposes, looks no different than a standard microphone. This tool adds new dimensions of truthiness to any standard interview. It can also easily be adapted for karaoke.

Don’t be intimated by the number of steps. It’s one of the least complicated projects I’ve ever made.

This project was initially developed with the love and support of the Eyebeam OpenLab.

Step 1: Go get stuff

You will need:
– A MQ-3 Alcohol Sensor (available via Futurlec. Allow a few weeks for shipping from Thailand. Be warned! Ordering anything else from Futurlec may place your order on backorder and leave you waiting a long, long, time without being notified).

Arduino Breathalyzer Microphone (1)

– An XLR microphone (you can pick up cheap dynamic XLR microphones intended for karaoke all over the internet)
– An Arduino Decimilla
– Logomatic Data Logger (via Sparkfun)
– An SD Card (can get a cheap 256MB card at Radioshack)
– An SD Card reader
– XLR to 1/4″ stereo plug
– A professional-looking audio device (working or not)
– resistors (100K, 10K, 1K)
– a schottky diode
– Acrylic or cardboard
– glue
– solid hookup wire
– 9V battery plug
– 9V battery
– isopropyl rubbing alcohol
– a 12 pack and some friends

(other stuff for interfacing Arduino and data logger?)

Soldering iron
Wire cutters
Mini screwdriver set
Needle nose pliers
Power drill or other rotary tool
Scissors, saw and/or laser cutter (see step 15)

Step 2: Remove the wind screen

Simply twist the windscreen counter clockwise and it should unscrew right off.

Step 3: Loosen the Mic

Loosen the mic from the casing by twisting them apart gently. That means that you need to simultaneously pull and twist to separate the two. The mic is usually glued in, but never well enough that can’t be defeated by some gentle force.

Step 4: Take out the switch

To remove the switch from the casing, the on off label has to be carefully peeled up. Be careful not to bend or destroy it, since you will be putting it back in place later. The best way to removed it is with a small flathead screwdriver or a safety pin.

Once the label is removed, there should be two screws. Unscrew these screws to free the switch from the case.

Set aside the label and screws for reassembly later. If you lose these, you won’t be able to reassemble this easily.

Arduino Breathalyzer Microphone connecting (1)

Step 5: Remove the XLR plug

Locate the screw at the bottom of the casing. This is holding the XLR plug in place. Unscrew this screw as well to free the XLR plug. Once you are done, set this screw aside.

Step 6: Take Out the Wiring

All of the microphone’s components should now be free from the casing. Gently pull on the microphone element to remove all the wiring from the casing.

Step 7: Prepare the XLR Plug

The XLR plug in most cases is probably setup for mono audio output. This usually means that two of the pins are grounded (notice in the secondary image how two round pins are connected to the flat ground tab).

For the purpose we are using the XLR plug, only one pin should be grounded. This means that the two round pins should no longer be connected. Take your wire cutters and cut away this connection. Bend any extra wire on these pins away from each other.

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