At 11:00 PM 3/31/2005 -0600, you wrote:
>I'm trying to build a little network of microcontrollers that can report 
>their status to a central server, in a forest. We want to make the various 
>flag/objective stations when we play paintball automatized, and I'm 
>looking for some ideas/recommendations. The uC need to report something 
>simple (eg, which sides owns that station), and maybe a timer. However, it 
>would be great to further expand it to use rfid/bluetooth technology to 
>record when a player is actually 'holding' the station. It would transmit 
>this data to a central server that would display the whole results.
>
>Any ideas for bluetooth/rfid/'presence' signalling?
>
>Even more importantly, should I try to use little rf transmitters, and do 
>it myself, or woiuld it be better to use 802.11 wireless types? The 
>picotux (recently posted, 
>http://www.linuxdevices.com/news/NS8386088053.html) looks great: I could 
>just use tcp/ip for reports and command line scripts, since they run 
>linux. But they are 100 euros a pop. I'm also concerned about how much 
>power consumption I should expect from these things, as well as what range 
>would I get in forests?

I faced a similar problem like this last year with some PIR monitors in a 
forest.

We first tried using 802.11 and found that if we had a clear line of sight 
between the sender and receiver
that it worked fine out to about 200 yards. Of course, we could only get a 
clear line of sight with 2 of the
senders. Without a clear line of sight, we could only get about 100 feet of 
reception amongst softwood
pines trees, and around 50 feet of reception amongst hardwood hickory trees.

The solution we used was to buy a bunch of the 2-mile range hand held 
radios and hack them apart.
We set them all to the same frequency, replaced the send button with a 
transistor to act as a switch,
and replaced the microphone with a simple beeping circuit run from a pic. 
Once the PIR was activated,
the PIC would broadcast its beeps 5 times.  (The beeps just identified 
which monitor it was - 9 beeps
for monitor #9).  On the receiver end, we had another hacked hand held 
radio with a PIC that would
count the number of beeps (voltage pulses) that came in and dump it into a 
computer serial port. A simple
basic program on the computer then logged the time and receiver number.

I think we pretty much got all of the basic circuits from a model rocket 
telemetry web page.

There is one problem with the system though. If two of the monitors 
activated at the same time then we
would get the wrong the sensor logged. (If sensor 1 and sensor 2 activated 
at the same time, then we
would get 3 beeps and the computer would log sensor 3). Luckily that only 
happened a couple of times
and when we looked at the data it was obvious that something had messed up.

Good luck
_____________________________________________________________
Cris Wilson
Information Resource Consultant
College of Architecture, Arts, and Humanities
Clemson University
cris@clemson.edu
To report problems email: aah_computers@clemson.edu




                                

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