Position Locator

Apologies if this has been answered before, I can't seem to find what I need though (might be the wrong search terms?).

In a nutshell, I have a datalogger I am building (328p-based) that I need to be able to locate and collect. I will know within a ~1/2-3/4-mile radius and with a fair degree of certainty as to the rough direction where it is, but not much more than that. It could be buried in the ground a few feet, stuck under a rock, sitting right out in the open, etc. I just need to be able to find it and gather it, I don't have to transmit any data back (it is logging to internal memory).

The size doesn't have to be tiny, but anything more than a couple cubic inches could be troublesome. It only needs to run for maybe an hour off of batteries (long enough to deploy and then go collect it).

Ideally I'd like something fairly ready-to-go that I can integrate into my device that is something roughly to a beacon. Think of spy movies where they can go find an object they put a tracker on (yea, I can't come up with a better example today...coffee time...).

The only half-solution I came up with was to put a GPS chip on-board and periodically transmit the coordinates. But I got hung up on a good transmission system (I do not want to go cellular). Ideally the solution would be something even simpler, but I'll listen to any ideas that will get me there!

Any suggestions?

The most straightforward solution would use GPS to work out its position and a GSM modem to report that position to you. That would get you to within tens of yards of it. A loud buzzer that you could trigger via radio would tell you exactly where it is.

If you want to eliminate the GSM part you would be looking for a wireless transmitter with a range of 1/2 … 3/4 of a mile instead. That sort of technology certainly exists, it’d just be a matter of finding something within your budget.

If I can get within ~20-30 feet (which I know is well within reason for GPS), that is good enough, I can search that small an area easily enough. But I'd definitely like to avoid GSM.

madmattd: If I can get within ~20-30 feet... I can search that small an area easily enough.

Just curious: How will you "easily" find a couple of cubic inch object buried a few feet deep in a 900 square foot area? Metal detector?

bigred1212: Just curious: How will you "easily" find a couple of cubic inch object buried a few feet deep in a 900 square foot area? Metal detector?

Well, the whole thing will be roughly the size of a bowling ball, just not all that room is available for the transmitter. It's a flight tracker if you will, somewhat similar to some of the rocket boards that are out there. If it happens to be buried, there will be an impact crater ;)

Well if you are dead against GSM, then you are probably looking at 433Mhz radio. Maybe send GPS coordinates in serial over radio. And then use PeterH's buzzer to get you the last 20 feet.

I've looked a lot into various options the last week or so. I found the perfect setup, very close to what I was envisioning and I think it would easily handle what I need: http://www.walstonretrieval.com/main.htm. But gulp on the pricetag, at roughly $750 it is WAY more than I was looking to spend. It is used typically for finding a crash model airplane.

An audible LMA (lost model alarm) seems to be what most of those folks use instead, but I doubt the range will be good enough on its own in a mix of open field and trees. In fact I'm almost certain it will not be. Might be handy for the last couple of feet as PeterH suggested though, I might add that in, a simple PCB buzzer would be easy enough and save a little extra time.

I looked at the 900MHz XBee Pros last night, and I wonder if they might do the trick if coupled with a GPS, I was specifically eying the Xbee XSC S3B models. Any folks have experience with them in an application such as this? Specifically, I'm hoping that they aren't super-directional, as the orientation of the datalogger unit cannot be guaranteed (upward, downward, pointing away, etc), and that the signal will still leak through a few feet of ground (I don't think it will get buried, but down a hole is possible). I'm familiar with using XBees (series 1) in both AT and API mode to transfer data between a computer and an Arduino, so I'm not concerned about the code end. Heck, I might just hook the TX of the GPS to the RX of the Xbee and not even run it through a uC. Just the actual radio communication aspect, well, I'm not terribly familiar with radio technology in general (though I've learned a lot while researching this project). From what I've read, it sounds like 900MHz is way better at penetration than 2.4G?

Since I will know the approximate line that the datalogger will be along, even if it is initially out of range, I figure I could get in range of it and then receive the GPS coordinates, and move in from there (either using my handheld Garmin trail GPS or even just my phone with an appropriate app). Or, since I know the line, perhaps put a 3rd Xbee on a pole 1500-2000 feet out or so (the first 1000-1500 feet will generally be open field) and use Mesh mode to hop the signal back to the main receiver?

This sounds like it might work fairly well to me, but I was hoping some of the "experts" here could add their opinion. It's not cheap, but it's not super expensive either so its a definite possibility and the best I've come up with thus far. If I'm off the deep end and I'm not likely to get good results, please let me know ;)

"If it happens to be buried, there will be an impact crater ",,,, and it will be easy to collect most of the peices.... Not too encouraging a project description. Google 'FM Wireless mike' use a ping circuit to provide an audio beep. IF IT SURVIVES impact, you can track with a dipole antena on a FM pocket radio. Good luck (your'e gonna need it)

123Splat: "If it happens to be buried, there will be an impact crater ",,,, and it will be easy to collect most of the peices.... Not too encouraging a project description.

Says the guy named 1-2-3-Splat :D

Here's a nifty lil FM tracking transmitter that could work for you... Easy to make, directions, parts list, and even the pcb silkscreen on the webpage.. So simple you might already have all the components already except for the crystal. http://www.jbgizmo.com/page30.htm

Probably one of your best options and super cheap to do. Low-budget is probably best considering the "projectile" style experience and impact it's going to receive.

madmattd:

123Splat: "If it happens to be buried, there will be an impact crater ",,,, and it will be easy to collect most of the peices.... Not too encouraging a project description.

Says the guy named 1-2-3-Splat :D

How do you think I got the nickname?