SparkFun Forums

[Tre]

I am working on a device that would be used to monitor the position of people (such as in a hospital environment). I would like to use GPS and some sort of transciever that can obtain good indoor and outdoor range.

My primay concern however, is certainly the indoor usage. Thus, I am looking for a transciever with good internal range and a GPS reciever that is able to get a signal indoors.

Secondly, size and power are always a concern.

Any suggestions on particular SparkFun modules would be greatly appreciated.

I am currently leaning towards the "High Speed Low-Cost Tranceivers - 2.4GHz with Built-In Antenna" and the "12 Channel Laipac PG-31 GPS Receiver"

Thanks!

[dpaton]

Tre-

I think you're going to have a real problem using a GPS receiver in a hospital environment. Knowing how those buldings are usually built, unless you have GPD repeaters on every floor, or are right up against a window facing the right part of the sky, you won't get a usable 3D positioning fix.

The problem is that the L-band frequencies that the GPS downlink is on don't travel thru concrete and steel, and the multipath distortion gets so bad inside a building because of that, the position fixes are generally tenuous at best, and definitely won't be accurate enough to find someone more generally than "within 30m of the building, on one of 5 floors", which may or may not be acceptable for you.

Also, unless your project is being supported by some member of th emedical community, you may run into trouble bringing a tranciever into a hospital. They try to regulate the emissions inside the buildings tightly,due to the effect that EMI can have on some of the more sensative equipment. Cellphones are generally required ot be turned off, tho I've seen a lot of people ignore that rule.

The way I've always contemplated doing something like this is either with a large mesh of RFID readers capable of a 2m range (>100V excitation, which may be verboten in a hospital) or a set of known power fixed beacons and positional triangulation based on received signal strength. Both put a lot of RF into the air, and both require significantly more hardware than just the subject tracking monitor.

Finally, the 2.4GHz tranceiver will have issues going around corners and through some walls, not only because it won't go thru metal very well, but because 2.4GHz is one of the 'water bands", where water molecules are excitable, and suck up a ton of power. Human bodies, plants, etc all impact the signal transmission in the 1.2, 2.4, and 5.8GHz bands (the higher you go, the worse it is). Off the top of my head, I'd say 419/433mhz ISM would be a a better option, or perhaps something way down in the open 49MHz band.

If you manage to pull this off, I'll be the first one to congratulate you, but I think the technocal obstacles need further investigation and perhaps a different approach.

-dave

[Tre]

Ok, I guess that I need to calify a little bit more. The device will NOT be used in a hospital environment, there are far to many regulations regarding RF noise and other issues there. It will however, be used in nursing homes. I would not expect a nursing home to be nearly as resiliant as a hospital in construction aspects. I would expect it to more accurately resemble a home.

As far as getting an exact reading, thats not necessary but a general vacinity is very important. You mention 30m radius, I would hope that I could come a little closer to 10m or so.

The transciever would relay to a base station (or multiple base stations) located in the home and potentially outside of the home. This would primaily be to help elderly patients from wondering off unfound for hours at a time. It would also be nice to have communication indoors, possibly trough 3 or 4 walls. If 2.4 GHz or 300Mhz transcievers are not reliable options, the next best would be a cellular module, although that would get very expensive quickly.

[carterbrock]

I have seen this done with active IR transponders and active badges on the personel. http://www.rauland.com/healthcare/tracer.htm is one such system.

[dpaton]

WAAS-capable GPS receivers like the Lassen IQ can get inside the 10m circle of confusion pretty easily if you're in range of one of the many USCG WAAS broadcast sites, which are generally within 100mi of oceans or the great lakes.

FWIW, I've seen nursing homes built like woodframe houses, but many more are built with steel studs and steel roof structures, since they are commercial buildings and almost certainly required to use metal construction to mitigate fire issues, at least in every community I've ever been in. The trend here in the midwest right now is nursing homes and elder care facilities to be built in high-rise style, to allow as much density as possible. Of course, that kind of concrete and steel construction would cause as manu problems as the hospital, and many of the larger facilities near me (Chicago suburbs) have rules similar to, if not the same as the local hospitals in terms of RF devices.

I think something like Carter's solution makes a whole lot of sense on a whole lot of levels. Just remember, RF doesn't mix well with medical devices. IR is an easy way to get around it.

-dave