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Xbees and rf modules

Hello guys. 

I was thinking about buying a few xbees for my lasertag project but since they're a bit costly i wanted to ask you if it fits my project before buying them.

I'll tell you what i want to to: basically lasertag is a game where there are lots of players that "shoot" at each other with IR pulses. What i wanted to add to it is some sort of "hit feedback", something, be it sound or LED, that tells me whether or not i have succesfully hit my target.

I was planning on having a "server" at the center of the playing field, and an xbee on every player's module. Once a person is hit, his system check the ID of the bullet understanding who shot it, then it sends a "this ID shot me!!111" code to the server xbee, which then sends it back to the ID of the shooter, and finally his system plays a sound.

Couple of questions:

a) is the server really needed or is player to player communication possible? Do consider that number of players might be around 4 per team or more.

b) since these modules cost a lot, could i have a powerful and costly xbee working as the server and cheaper ones on each player's module? Say the server xbee is a 60mW pro and cover 1.5km, does that mean that a player at 1.5km can also have a weaker 500m module or not (as long as he is in range of the powerful server xbee)?

c) is there a better solution to xbees or any tip you'd like to give me?

 

thanks!

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have you had a look at quasars 2.4ghz tranceivers?

the maplin link is here

and the manufacturer link is here

Looks like the range on those is too limited, i'm looking for about 200m.

I gotta find myself some more powerful modules i think. Datasheets say these things reach a distance of around 150m. I would need something like 250m to be 100% sure it is gonna be transmitted. Anyone know of something capable of that similar to these modules? (or even different, as long as it is cheap :=) )

Just saw rik's post!

While i was eating pasta, i came up with the following facts:

-IR beam's range is at most 200m, at "very" most.

-to hit a player there have to be no obstacles in between

now, I ANDed the above statements and remembered rik talking about achieveing a range of about 200m or more in open space, so i guess Easy Radio or similar modules might work, not to mention i have one in my "electronics box". Why didn't i think of that before? Silly me.

Thanks for reminding me of the easy radio modules :=)

It all comes down to distance. If 200 m is the absolute maximum transmit/receive distance, then MAYBE you could use the 434 MHz radio links (don't call them Easy Radio unless you're willing to pay much higher prices). And there are a lot of prerequisites there:
1) big antennas, on both sides
2) sit still, well at least your central server should
3) more volts is bigger signal, this means more batteries on the person/shooter/victim
4) one direction only, victim signals to server, no talking back
5) all transmitters use the same frequency, so don't keep broadcasting or you will block the channel for others
6) use short data bursts, but also repeat your data/info, use checksums
7) altitude, higher antennas are better

I suggest every victim keeps his own score on a uC and transmits it to the server at (ir)regular intervals. Don't send messages like "I've been hit again" and trust the server to count them all up. This would violate rule 6).
Worst case: your scores finally make it to the server once everybody gets together after a match. Probably next to the server,

Hey thanks for the infos rik!

The point is not really keeping track of the score, since that can be done at the end of the match with cables (everyone gets back to the main base and uploads the score to some computing machine.

What i am looking for is a fast way to tell the shooter he has hit the target. I think i might stick with those modules (easy radioish) but maybe not exactly the ones you used, as official datasheets talk about 150m while the IR could get up to 200m. I guess i would need to go for 250m rf modules to be 100% sure.

Gotta find myself a more powerful module maybe.

When they say "150 m", they mean "you should expect something in the neighbourhood of 150 m depending on all that shit Rik talked about".

And you're right. There is no way my modules will give you an immediate, guaranteed notification that you've hit something in the last second. But then again, what marksman at 200 m would get that kind of data in the heat of battle?

True. As usual the best way of understanding if things work is just testing them. I've found myself something to do that will keep me busy tomorrow :=)

I'll have to test both range and speed. They're both a great concern...if it's not fast enough (say 200/300ms at most) then it's gonna become more annoying than it would be useful. 

 

EDIT: I'm not sure i should trust those guys but....they're extremely cheap, no shipping charges and 500m (hope it's true)! :O http://cgi.ebay.com/RF-RFID-Transmitter-module-315MHz-500-meter-9906A-/130422527383?pt=LH_DefaultDomain_0&hash=item1e5dc9d597#ht_687wt_1137

 

I'm not sure, but I think 315MHz modules are not allowed in europe and these are only transmitter modules, no receiver. 433MHz and 868MHz is ok in Europe, 433MHz gives you a greater range. Maybe the RFM12 transceiver modules is an option too or the RFM02 when you only need a transmitter, they are cheap and should work >150m. With a better receiver antenna (Yagi) the range should be more than 200m.

Thanks RobotFreak.

They do look very interesting, i'll see if i can find a distributor for those.