Tracking Device Progress

Once again, it's been a while since I've made a new post (seriously, it's becoming cliche). But that doesn't mean we haven't been working hard at our project. In fact, we've made some serious progress on the Arduino based tracking device. After realizing we had a major oversight concerning radio communication, we decided to change our methods from serial communication to DTMF (Dual Tone, Multiple Frequency) communication. Don't know what DTMF is? You know the sound you hear when you push a number on your telephone? It's that. The tones you hear through your phone are actually a combination of two frequencies. Each number on the phone corresponds to a unique combination of two of a set of frequencies. When the telephone station (or whatever it's called) receives these tones, it recognizes the combined frequencies as a set of numbers, and takes action accordingly. What exactly does this have to do with our project? Well, because audio signals transmit over radio much better than binary signals, we've decided to use dual frequency signals to communicate the latitude, longitude, and altitude values. We have an IC (integrated circuit) that will take in binary data and convert it to these tones, so we can easily plug output of this chip into the mic of a radio, and plug the speaker of the other radio into a computer to interpret the signals.

DTMF tones of different numbers

So we have a language to communicate the data, but we also need a way to get the data. You may think it's pretty simple, just take the GPS data and plug it into this magical chip. However, we have to convert the GPS data, which is stored in "float" (a type of variable which has numbers after the decimal point), into an array of numbers, so that they can be called individually. After a long time programming, filled with frustration, we finally got it. The video you see below is the GPS data being converted to individual numbers, and then displayed sequentially as binary numbers in four bits. It's probably hard to tell what the numbers are because the LED's are so bright, but the sequence is 2,6,3,7,8,0,3,7,8,4,0,0, and then it repeats again after all the LED's go on. This means that the location in "minutes" (1/60th of a degree) is 26.3780 by 37.8400. I disregarded the degrees because the balloon's trajectory should not cover more than a degree of latitude, and if it does, we'll know which degree area it is in anyway.

Now, all that's left is to get all of the hardware ready and test the range of the radios. That's still a lot of stuff to do, and we only have under 3 weeks left. This is the part of the project where stress levels rise to a record high. I'm fairly confident we can get all of it done, but we're nowhere near where I thought we'd be at this point. What's left on the shopping list? The balloon, the helium, and any materials we need to fashion the capsule. Oh yeah, and another unexpected cost came up recently. As it turns out, the radio range of 40+ miles is only reachable in the GMRS setting. And the FCC requires you to have a license to operate the GMRS channels. And the license costs $85. Yeah. Donations, anyone?