Introduction: Discreet Data Logger

About: My name is Randy and I am a Community Manager in these here parts. In a previous life I had founded and run the Instructables Design Studio (RIP) @ Autodesk's Pier 9 Technology Center. I'm also the author of t…

There is no better way to hide a covert device than to stick it inside a larger conspicuous device.

That said... Essentially, this is a guide for making a data logging system for use with the breathalyzer microphone.

To accomplish this, an Arduino and a Logomatic SD data logger are embedded into an old and considerably large tape deck. The data is fed into the tape deck through an unassuming 1/4" audio jack.

Step 1: Go Get Stuff

To do this, you will need...

- old tape deck or similar
- Arduino Diecimilia
- Logomatic V1.0 SD Data Logger (available from Sparkfun)
- SD card
- An SD card reader
- A 10K resistor
- A schotky diode
- 1/4" jack (unless you already got one fo the breathalyzer mic)
- 9V battery connector
- 9V battery
- hookup wire
- electrical tape

- philips head screwdriver
- soldering setup
- pliers and/or cutters
- power drill

Step 2: Prep the Case

The first thing to do is open the case and determine where the arduino, data logger, battery and 1/4" jack are going to be placed. This may mean, in many cases, removing some of the parts inside the device.

I decided that the best place to insert my electronics was in the battery slot of the tape player. Unfortunately, the battery slot was just slightly not deep enough for the Arduino. This was easily resolved by disassembling the case, breaking off some excess plastic and reassembling.

Once the plastic was broken, everything fit in with room to spare.

The only real rule with this is that there needs to be enough room to comfortably fit all of your parts inside. Don't forget to factor in a reasonable place for mounting the 1/4" stereo jack without creating too many problems.

Step 3: Insert the Stereo Plug

Once you have carefully determined where the stereo plug should be positioned, double check that it will actually work in that position. Once you are absolutely sure, drill a 1/4" hole in the side of the case. Pass through your 1/4" stereo plug from the inside and secure it on the outside with the mounting bracket.

In my case, I didn't have to drill a hole. I was able to pass it through an existing hole in the case and secure it that way.

Step 4: Prepare the SD Card

Plug your SD card into the card reader for your computer. Format the card to FAT 16. Once this is done, unplug the card and insert it into the Logomatic.

Step 5: Setup the Logomatic

Basically, this involves inserting the SD card into the socket on the datalogger and applying power from the Arduino.

Wait for a few minutes. You should see a flashing sequence of lights. When the lights are done flashing, remove the card and put back into card reader.

Two text files should appear called ___ and ____. You want to open them and configure it to have the following settings ______

Step 6: Build the Interface Circuit

Using the following schematic, build the circuit to interface the Arduino to the Datalogger.

Step 7: Program the Arduino

Program the Arduino with the code found below.

In other words, download this code. Download the Arduino development platform. Load this code into the Arduino development platform. Once the code is loaded, hit the upload button as shown in the picture below.

That's about it.

Step 8: Connect It All Together

Connect the Arduino to the Logomatic data logger using your interface circuit as pictured.

Step 9: Finish It Up

Plug the positive battery terminal into 9V socket on the arduino and ground to ground. secure everything inside of case so that the terminals can't accidentally touch. Finish by closing up the case.

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