I'm currently looking for options to build a 3 piece game for an outdoor activity company based around the warmer/colder game.

  • Two teams are each issued a receiver, and each team starts around 400 meters apart.
  • In between the two teams is a transmitter, which is the objective.
  • The receiver units periodically emit a "ping" sound.
  • The intervals between each "ping" sound become shorter the closer the receiver gets to the transmitter.
  • The teams are released in to the play area, which will be a forested area, to hunt for the transmitter.
  • The first team to reach the transmitter is the winner.
  • The transmitter/receivers should be able to run for at least 4 hours on a LiPo.

I'm not generally a low-level engineer. I'm quite experienced with Arduino/Netduino/Zigbee/Xbee, but nothing lower level with that really.

My initial idea for this was to use the RSSI output from an XBee on each receiver to measure the signal strength, and parse that with a small Arduino in to whatever output I wanted. The issue with this idea, is it relies on two transmitting XBees, and two Receiving XBees, as well as two Ardunios. Quite an expensive build! (two of each pair so the receivers don't measure the distance to each other!)

I'm pretty certain there is a significantly cheaper way to implement this, as PMR radios (for example) are able to meter signal strength), and you can even get those little WiFi key chains that show signal strength around you.

Would love to know peoples thoughts, or even if somebody has done something like this before a block implementation would be great!

  • 2
    \$\begingroup\$ RSSI is a pretty rubbish way of determining distance. Also, radios change their power output to compensate for noise, received power and multi-path effects. Take a look at chirp spread spectrum. Devices exist that can measure distance to a few cm by measuring round trip time. \$\endgroup\$
    – Jason M
    May 12, 2012 at 22:20

1 Answer 1


Different: Place a GPS receiver in each "receiver". Program target coordinates in each rx. Go. Vegetation will affect the result.


Location of transmitters by competing teams is traditionallyknown as "Fox Hunting". Traditional "Fox Hunt" transmitter hunters use directional aerial with nulling. Receivers CAN be very simple - essentially "crystal sets" in some cases. Others use very complex systems.

Extremely good paper on Fox Hunting systems

Good but complex VHF system
.. manual for: Use of Mk4 Foxhunt receiver for pulsed signals


More ...

80 m = 3.7 MhZ FH rx

  • 1
    \$\begingroup\$ Some Arduino specific code and information on setting up and using sensors, such as your purpose: Sensor Workshop \$\endgroup\$
    – rdivilbiss
    May 13, 2012 at 14:53

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