Wile I was working with Niewma Systems, a Swiss gun range nearby needed some way to signal from the firing position to the target bunker that the shooter was finished firing.  They had a system in place a while back, but that had broken.  They ran cables under the lake in between the two areas and used a simple switch/light set up. When someone was done shooting, they would hold down the switch, which would light a light under their target.  Someone in the bunker that was holding the target would then pull it in, mark the score, and put the target back up.  They wanted something that would be robust, consistent, and that wouldn’t deviate from the previous system, meaning people wouldn’t need to learn something totally new.   The distance was about 300m (just under 1000 ft) and each end only had a car battery for power (12V).  They also wanted something that was either indestructible or moveable because the range is out in the country and not protected/guarded.

What I ended up doing was essentially trying to replace the cable with something wireless that took no setup once connected.  Xbee seemed to fit the bill pretty well.  The 1.5km range (with line-of-sight) of the pro version gave a little buffer room in case something wasn’t ideal.  I could also pair the two modules ahead of time to make sure interference wouldn’t be a problem and that it was plug-and-play.  Arduino also proved a very simple platform to implement this.  A simple loop was used to constantly read the state of the input buttons, which was sent to the other device.  If the entire string arrived properly (basic error-checking), the receiving device would turn on some LEDS as indicator lights using the wiring already in place.

The system worked very well for them.  They added some connectors at each end to make it more plug-and-play.  One connector connected all necessary wires as well as power.  They’ve used it for a couple tournaments so far without a problem.