The nature of this tracking device is extremely limited and technical, but if you can hack it, this really works -- and that in itself is really exciting. The limitations are at times frustrating:
- The 2-way radios necessitate a linear or nearly linear sight on your tracking device (which in many cases may spoil the whole point anyway).
- You must be closer to the transmitter than the nominal range of your radios.
- The tracker can get bulky (think about it -- you're basically lashing together two electronic devices that were originally meant to work separately).
- This one is the worst limitation: you will need to be able to manually sift through the static garbage that radios usually emit to find the data your GPS is trying to send. If you are a total 1337 h4ck3r, you may be able to write a program that pulls it out automatically and feeds it into Google Earth. (If, incidentally, you do accomplish this, tell me what to do to gain your favor when you take over the world.) Beware! Radio static can get really random, and will even imitate the data you are after, often giving you misleading results.
To quote, with a slight change, someone who inspired me to think this way: "If you can't modify it, you don't own it!"
Building on that, the lesson I have learned and hope to teach others is that something's label should not limit the way we use it.
Step 1: Gather Supplies, Tools, and Materials
Get a cable that connects the GPS to a computer. For my project, I used a COM port plug, since I already had it lying around, but I suspect using a USB connector would have been slightly easier.
Get a pair of walkie-talkies (Americanese for 2-way radios) that have an impressive range. For this example, I am using a pair that boasts a 12-mile range.
Other materials included in this project: Wire, solder, batteries, a computer, and glue or epoxy. Optional: something to track.
Tools you will use include: wire cutters, wire strippers, screwdrivers, pliers, a soldering iron, a DMM (Digital Multi-Meter), scissors, an undefiled radio, and the user manual of your GPS.
Find a quiet, peaceful place to fine-tune this. Several of the steps are bound to be frustrating for a first-timer, as they were to me.
Step 2: Break It Down
I use scissors to cut and strip my wires, but that is because 1) I am too lazy to get the wire cutters and strippers out, and 2) I don't care about how dull I make the scissors. I find them to be both convenient and dangerous. Be careful!
Next, open up the radios. Spend some time with their insides. get to know them. Maybe take them out for a nice dinner or a walk on the beach. Carefully solder out the speaker on one, and the microphone on the other. I tore them off using pliers, which in retrospect was a stupid risk, and I was lucky nothing bad happened. Make a note of the contacts on the circuit board where those components had been. You'll be using those contacts later. Toss the speaker and the microphone into your spare parts bin.
Step 3: Wiring the Transmitter
If this info isn't in your manual, you can determine which two wires you are interested in because a strong current goes across them when your GPS is attempting to transmit information. When applied to the tongue, it feels like quite a kick, while combinations of any other two wires are barely noticeable. Don't shock your tongue for too long, or it will go numb and probably even get injured.
Also keep in mind that the polarity of the contacts is important, so don't make the connection permanent. Once you are sure the contacts are in the best position and polarity possible, solder them good and then glue them down for sturdiness. I used hot glue, but I think epoxy would have been a lot better.
Step 4: Wiring the Receiver
Twist together and solder the wires that correspond to pins 2 and 3, so that you get one node out of the two pins. I'm not sure why the receiver won't work if you don't do this, but it took me six hours of fiddling with it before I figured that out.
Connect the wires to the contacts in the receiver that used to host the speaker. Again, polarity in this is important, so test everything before making it permanent.
Step 5: The Software Side
Step 6: Bridging the Gap
Initially, my GPS com signal was strong enough to tell the transmitting radio when to transmit and when to relax. I'm not sure why it was fine before, but now the transmitter omits the North coordinates unless the PTT button is held down, so I'll have to tape it down when tracking something.
Once all this is set up and the radios are both on the same channel, make sure the receiver is on full volume so Earth Bridge can hear it. Click the "Connect" button and it should immediately start spewing garbage onto the text box. If you study this garbage for a while, you should notice a pattern that follows specific rules about what the GPS is trying to say. You can use these rules to sift through the garbled mess to pick out coordinates. (If you happen to have a Garmin sending text at 1200 baud, and for some reason also have WordPerfect 12 on your computer, I have written a few rule-based macros you can use to sift through the radio junk quickly!)
When you start to recognize what your coordinates look like, you can type them in as a placemark in Google Earth and see precisely where your tracking device is! After a lot of practice, this process can be compressed into a 2-minute frenzy that makes you look like a computer hacker from the 80s (wear steampunk goggles and gloves for full effect)!
Backing up a bit, if you have everything set up but are not receiving any signal, or just a completely unusable signal, it is very likely that the polarity on your receiver or transmitter is reversed. Try reversing the contacts on either device (or, in my case, both!) until you receive a usable signal.
Another good way to test the transmitter is by using a radio you have not hacked apart. Listening to the transmitter through the test radio should sound a bit like a broadcast from the Emergency Broadcast System (which makes me wonder if that is a string of data they're broadcasting). After tweaking with everything for a while, you'll get a really good idea of what it is supposed to sound like.
Step 7: Power Options
I tested my setup with rechargeable batteries. My radios take 3 AAA batteries, and my GPS takes 2 AA batteries. I used AAA batteries rated at 1000 mAh, and AA batteries rated at 2600 mAh. Initial calculations led me to predict that the transmitting radio would last 2.5 hours. Based on this, I'd recommend that your transmitting radio batteries have the highest mAh rating possible. If you're doing long-term tracking, this isn't for you.
Interestingly, the receiving radio hardly uses its batteries at all. I gave mine a fresh set of alkaline AAAs at the beginning of this whole ordeal and haven't changed them once.
I gave my transmitter a second test a bit later, using D-sized 12000 mAh batteries (yikes!). They survived more than 24 hours of transmitting, but I'm not sure exactly when they died because I left it alone for too long. This was when the GPS did not omit the North coordinates, so I'll have to do another test with the talk button taped down and post the results here.