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:
- An MQ-3 Alcohol Sensor
- An XLR microphone
- An Arduino
- Logomatic Data Logger via Sparkfun (obsolete) ***
- An SD Card
- 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
- hookup wire
- 9V battery plug
- 9V battery
- isopropyl rubbing alcohol
- a 12 pack and some friends

*** This might work as a substitute, but would require some modification.

Tools:
Soldering iron setup
Wire cutters
Mini screwdriver set
Long nose pliers
multimeter
Power drill
Scissors, saw and/or laser cutter (see step 15)

(Some of the links on this page contain affiliate links. This does not change the price of any of the items for sale. However, I earn a small commission if you buy anything and reinvest this money into materials and tools for future projects.)

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.

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.

Step 8: Prepare the Switch

Preparing the switch is easy. Only the red wire coming from the XLR plug should remain connected to the switch. Cut away all extra wires with your wire cutter.

By doing this, you have just cut free the microphone element. This is a perfectly good microphone and element and could be used for a host of other projects. Store it away somewhere safe.

Step 9: Attach More Wires to the XLR Plug

Attach a wire that is about 8" long to the one pin on the XLR plug that is no longer connected to anything.

Also, take your wire cutters and remove the remove the remaining black wire. Replace that black wire with another black wire that is 8" long.

Step 10: Attach More Wires to the Switch

Attach a red wire that is about 6" long to the tab on the switch that used to be connected to the microphone, but to which no wires are currently connected.

A good way to figure out which is the right tab is by figuring out which two tabs the slider button is directly above when the microphone is turned on. It is these two tabs that need wires connected to them. One should already have a wire connected to it (probably the center one). It is the bottom tab that needs to have a wire connected to it (there should already be some solder on the pin, since you cut a wire off of it earlier). If you are still confused, just look at the pictures below.

Step 11: Reassemble

Reinsert the wiring into the microphone casing starting with the XLR plug. The XLR plug probably needs to be orientated in the right direction to be able to slide in. Look for guides on the side of the plug that need to be lined up right.

It helps to push the XLR plug as far as you can in using your fingers and then to pull it through with a pair of needle nose pliers.

Line it up correctly, and reinsert the screw you removed earlier.

Next, hold the switch in place with your finger and screw that in as well. Once that is screwed in place, stick the "on/off" label back on.

Make sure that the switch is orientated correctly with the label. In other words, when the switch is put in the "on" position, it should be sitting directly over the two tabs with wires attached to it.

Step 12: Test Your Connections

There should now have 3 wires sticking out of the top of your microphone casing. If it hasn't been done already, strip about an inch of plastic off the ends of each of these wires.

Using the continuity tester on your multimeter (normally has a picture of a diode next to it) touch one probe to one of the pins on your XLR plug and then, one at a time, touch each wire at the other end. For each pin, there should only be on corresponding wire that gives a positive reading of being connected.

If more than one wire gives you a positive reading, you need to remove everything once more and check the connections.

Also, if you find a pin that does not seem to be connected to any wires, try turning the switch on. If that still doesn't work, you need to disassemble and re-check your work.

Speaking of the switch, be extra careful to make sure that the switch both turns on and off.

Step 13: Prepare the Stereo Plug

Cut two red wires and one black wire of about 6" length. The black wire should be connected to the tab for the larger audio terminal. The red wires should go to the other two pins which include the smaller terminal and the barrel jack.

Step 14: Test Your Connections... Again

Before all of the components are soldered in place on the microphone, it would be ideal to determine which wire is going where when the XLR cable is connected.

So, first of all, connect the XLR cable to the microphone. Connect the other end of the cable to the 1/4" plug.

With the continuity tester on your multimeter test to make certain that the black wire connected to the 1/4" plug makes a connection with the other black wire coming out the top of the microphone.

Next determine which red wire coming from the 1/4" plug corresponds to the red wire coming out of the top of the microphone that is connected to the switch. This is easy to test because when the switch is turned on, they should make a connection and when the switch is turned off, the connection should be broken. Once you found these two wires, mark them with a piece of tape.

For good measure, double check that the other two red wires that aren't marked also make a connection when tested with your multimeter.

Step 15: Mounting Bracket

Attached is a file for a mounting bracket which will fit snugly inside the opening in top of the microphone (at least my microphone). You may need to adjust the diameter of the outside circle to be sized correctly for your microphone.

This file is set up for a laser cutter and can be used to cut out the bracket in seconds should you be lucky enough to have access to a laser cutter.

If, like most people, you don't have access to a laser cutter, this file is still very helpful to you. You can print it out on any sheet of computer paper and then cut out the outer circle with a pair of scissors. Once this is done, tape this circle to whatever material you wish to make this bracket out of. Once its taped down, use this as a guide to cut out a circle and drill holes. I recommend using wood, acrylic or a thin, sturdy, board-like material.

Step 16: Start Soldering

Pick one side of the bracket to be the top and insert resistors through the outter holes so that one sits nicely on each side (forming a V-shape).

Twist together the two closest metal leads and then connect them with solder.

Step 17: Finish Soldering

On the side of the bracket upon which you inserted the resistors, insert the alcohol sensor.

Flip over the bracket. There are two groupings of three pins coming from the sensor.

For the first grouping of three pins, you are going to want to connect one of the outside leads from the resistors to one of the outside pins in the group. Then, you will need to solder the other resistor lead to the middle pin.

Once those connections are made you will need to solder the wires from the microphone. Solder the black wire also to the middle pin. If it is easier, you can also solder it to resistor lead connected to the middle pin.

Next, solder the red wire that is not connected to the power switch to the other outside pin that resistor lead is connected to.

Lastly, it is now time to connect the red wire coming from the power switch to the sensor. This wire gets connected to the grouping of three pins that you have yet to connect wires to (the one furthest from the resistors). Simply wrap this wire around either of the two outter pins and the center pin and then, in turn, solder it to the outter and center pin.

Step 18: Glue the Bracket in Place

Position the bracket neatly in place. If this looks good, take it back out of place, put some glue on the sides/underside and put it back once more. Try to keep from getting glue in the treads for the windscreen or you'll never get it back on.

If you sized your bracket right, you won't need all too much glue to hold it in place, since it should stay pretty securely on its own.

Step 19: Put the Windscreen Back On

Once the glue is dry, put the windscreen back on by twisting it on clockwise.

Step 20: Make a Discreet Datalogger

To make your mic truly portable, you will need to make a discreet datalogger as seen in this Instructable.

Step 21: Program the Arduino

Below is the code needed to test the Arduino.

First, open the Arduino development environment. Next, load up the file found below. Lastly hit the "upload" button.

Note: Older version of the Arduino may require hitting the restart button first before uploading

breathalyzer.zip
Download

Step 22: Testing... Testing... Is This Thing On?

I found the easiest way to simply make sure that its working is to turn on the serial monitor, wet a napkin with isopropyl alcohol, place the napkin near the windscreen of the mic and to blow. This should increase the resistance on the microphone and make the numbers that you are seeing increase.

If you really want to test it, you are going to need to get some beers and a couple of friends. Monitor their alcohol intake. Vary the rate at which they are drinking. Also, take note of their height and weight to accurately calculate their intoxication level.

Or... you could just bring it to an art opening and see what happens.

Step 23: Taking a Reading

To take a reading, approach your subject and turn the microphone on at least one minute before having them speak into it. About thirty seconds into the reading turn the microphone off to take a string of "zero" readings. This is important because it is the initial reading taken within the first thirty seconds that you need to clearly delineate.

Once you turn the microphone back on, it probably will no longer be completely accurate and need some time to reset.