Weekly Project: Noggin Logger--A Wearable GPS Data Logger

Where have you been? And, where did you go today? While words can aptly describe your daily activities, a picture can communicate around a thousand words, or something like that. Better yet, take that picture and wrap it around a fistful of GPS data and now you're really talking.

The GPS Logger V1.1 kit from Spark Fun Electronics (#GPS-00671) is a complete plug-n-go solution for logging every step you take during a day, a week, or, even almost, a month (in KML logging mode). Just pop in some batteries, flick the teensy switch, and within a couple of minutes you'll know exactly where you're standing when you flicked that teensy switch.

Based on the Lassen iQ GPS module by Trimble, roughly every second is recorded with the Spark Fun Electronics GPS Logger V1.1. You can select between The National Marine Electronics Association (NMEA) data or Keyhole Markup Language (KML) data. The latter has been uniquely massaged for assimilation directly into Google Earth coordinates format.

If you're a data miser, though, you'll probably opt for logging the NMEA data. As such, your GPS plate will be full; very, very full of data. Specifically, there are two lines of GPS data recorded every second with the GPS Logger V1.1:

$GPGGA,220536.00,3024.9664,N,08849.1198,W,1,04,3.70,00023,M,-026,M_*52

$GPVTG,236.3,T,235.2,M,000.0,N,000.0,K,A*21

Where:

• $GPGGA-Global Positioning System Fix Data
• 220536.00-Coordinated Universal Time (UTC)
• 3024.9664,N-Latitude
• 08849.1198,W-Longitude
• 1-GPS Fix
• 04-number of satellites being tracked
• 3.70-horizontal dilution of position
• 00023,M-altitude above mean sea level in meters
• 026,M-altitude of mean sea level in meters
• *52-checksum
• $GPVTG-velocity/track made good
• 236.3,T-heading in degrees
• 235.2,M-magnetic heading in degrees
• 000,0,N-ground speed in knots
• 000.0,K-ground speed in kilometers per hour
• *21-checksum

Armed with your prodigious pile of GPS data, you can view your whereabouts inside Google Earth. But getting the raw data into a brag-worthy picture could take longer than the trip you just logged. Some deft fingered text manipulation with an industrial-strength text editor (e.g., BBEdit) and Microsoft Word can convert your NMEA data into useable KML coordinates in a matter of minutes.

So where can you carry this fancy GPS logger? Well, use your head, man; literally. The GPS Logger V1.1 will easily fit inside the top peak of a baseball cap. Just route the embedded antenna out through one of the cap's ventilation holes and you'll be loggin' in no time.

Ja, das ist der Noggin Logger.

Time: 30 minutes
Cost: $153.70
Difficulty: Easy

Parts List

• GPS Logger V1.1 kit from Spark Fun Electronics ($150.70 #GPS-00671)
• Velcro Brand Sticky Back Tape 3-feet x 3/4-inch ($3; craft center)
• scrap fabric swatch (FREE; scavenged)
• baseball cap (FREE; repurposed)

The folks at Spark Fun Electronics have made the assembly of the GPS Logger V1.1 kit pretty much foolproof. Slip in the coin cell battery, insert the blank SD memory card, snap four AA-size batteries into the holder, and attach the battery holder plug to the PCB battery connector.

Route the embedded antenna through one of the small eyelet ventilation holes in the top of the baseball cap. Plug the antenna into the bottom of the Lassen iQ module. Snap the module onto the PCB connector.

Cut an oversized round piece of scrap fabric for the liner of the baseball cap. This piece of fabric should be big enough to cover the entire GPS Logger V1.1, plus add a seam allowance of 5/8-inch around the perimeter of your scrap. Slowly roll this seam allowance toward the inside of the fabric swatch, press it with an iron, and stitch it down.

Line the inside of the cap's peak with some Velcro Brand tape hooks. Make sure that you have ample hook pieces for holding the GPS Logger V1.1 and the fabric liner. Attach Velcro Brand tape loops to both the underside of the GPS Logger V1.1 battery holder and the bottom of the fabric liner. Press the logger into place, then install the fabric liner.

Pull the fabric liner aside and flick the power switch on the GPS Logger V1.1. In about 2-5 minutes, you'll be logging NMEA GPS data. Don't just stand there, don your chapeau, and get loggin'.

At the conclusion of your journey, pull the fabric liner aside, turn off the power, and remove the SD media card. Use any SD media reader to transfer the files onto your computer. The data is platform independent so you can read and massage your GPS content on any computer that can read an SD media card. You should have at least two files on your properly logged card:

• GPSx.TXT
• GPSCON.TXT

The GPSCON file is used for selecting either NMEA data (i.e., "NORMAL") or KML data (i.e., "KML"). The other file (or, files; files are sequentially numbered GPS1, GPS2, etc. for each activation of the logger's power switch) contains the GPS data. Now it's data crunchin' time. Here are a couple of shortcuts and tricks that you can use with BBEdit for quickly trimming your data fat:

• Delete lines that contain "$GPVTG" - removes all velocity & heading data
• Find/Replace "," with tabs
• Use MS Word for converting tabbed data into a table
• Move/delete columns
• Convert table back to text
• Back in BBEdit, Find/Replace tabs with ","
• Delete Line Prefix "0"
• Insert Line Prefix "-"
• Move those decimals with wildcards

If you'd like to retain as much GPS data as possible and disdain the KML data mode, you can reprogram the GPS Logger V1.1 yourself. Spark Fun Electronics has the firmware and an LPC Serial Port Programmer for getting the job done.

Write a KML shell for holding your coordinates, altitude, and other pertinent GPS data. Consult the KML 2.1 Reference for adding appropriate tags. Insert the data, fire up Google Earth, and open your KML file.

Now, THAT'S, where I've been.