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Measure distance between players in the field via radio?

  1. Apr 25, 2010 #1
    I would like to measure the distance between team players in the field.

    I need a device that can signalize when a distance between 2 players of the same team approaching a certain distance (2, 3 or 4 meters).

    The device must be relatively small (in order to have in on a players), to measure an accurate distance (~ +/- 5%) and have to provide the signal in real time (less than 1/2 Sec.)

    Is that possible with common circuits available.
    I'm not an engineer of any sort please keep it in layman's terms.

    Thank you.
  2. jcsd
  3. Apr 25, 2010 #2
    One of the things about radio waves is that if you want to get an accurate measurement of distance then the wavelength needs to be on the same order or smaller than the geometric features. At 2 meters, the frequency would have be 150GHz.

    GPS is not accurate enough for what you want.

    Ultrasonic range finding could be a good choice. One master device could send pulse. All smaller devices could send back their ID codes. A listening device could calculate everyone's position from that. This option is going to require a good knowledge of digital signal processing.

    The best option would probably be to implement some sort of motion capture technology with a camera. Have you ever seen in tennis games where a player challenges a ruling and a computer traces the ball's path to verify the call? Maybe you could put the equivalent of a tennis ball on your players and a computer could track their location.
  4. Apr 25, 2010 #3
    You need to give the issue considerably more thought and define some parameters.

    First of all what do you mean by 2 metres distance?
    2 metres from what part of the player? The kicking foot? the back of the head? what if the player is lying prone?

    Then you need to clarify, can each player in both teams be required to carry a small electronic device?

    Then there is the question of who is notified when the trigger distances are reached?
    The player? Someone monitoring, who is not playing?

    Then there is the question of budget.

    I could conceive of a sytem where each player wore a small transponder which transmitted an ID signal to two fixed base stations. These would each perform a distance measurement and pass the information on to a computer. These two distance would be enough to 'fix' the transponder's momentary postion on the field. The computer could perform the distance calculation to every other transponder and display as required.
    This measurement and display process could take place up to 1000 times per second which would be fast enough I'm sure.

    We use something similar for using oil rigs about, but it is not cheap.

    If this is a university project, perhaps your surveying department has an old Syledis or Trisponder that could be pressed into service.
  5. Apr 25, 2010 #4
    Thank you
  6. Apr 25, 2010 #5
    It's a long time since I worked offshore. Both Syledis and Trisponder are obsolete today, but there is plenty about them on Google.
    Modern miniaturisation should be able to make the kit small enough to clip onto a belt, but i think you would need some zeros on your budget.

    Good luck. I will post again if I think of anything better.
  7. Apr 25, 2010 #6
    This is not true. I used to work for a company that manufactured units that worked in LF (200 - 400 kHz) to determine distances from about 20 to 100 feet. It's advantage was that it worked in the near field where signal strength drops off faster than 1/distance^2. Once set up properly, they were quite accurate and immune to multipath.

    All good points. In addition, no radio antenna has an isotropic pattern (equal radiation in all directions). This means as players lean in different directions, the signal strength between them will vary not only due to the distance between them but also from the relative angles between their antennas. Also presumably the tranceivers would each have to transmit on a unique frequency and receive the frequencies of all the other players. This would be difficult to do in a half second. There are ways of doing this but they are quite elaborate and expensive.
  8. Apr 26, 2010 #7
    I was thinking of using one frequency and digitally coded pulses. There are only 20 something players to code. Say the pulses were 10 microseconds long, you could get 100/2 pulses per millisecond.

    The system works by having two or more base stations set up outside the playing field. These constantly send time of flight interrogating pulses to the mobile transponders. The return signal time would indicate distance and a computer could solve the positioning calculation on the field for each player. It could then solve the interplayer distances.

    The problem is that the information available would be off field.

    I suppose the computer could be programmed to send an alarm signal to players approaching too closely.

    I think there would be no problem in the 2.4 or 9.6 Ghz range, both available for public device use, to cover the field at adequate resolution and speed.

    But it would not be cheap.
    Last edited: Apr 26, 2010
  9. Apr 26, 2010 #8
    Well waddaya know?

    Bought my first Everyday Practical Electronics for ages (May 2010 issue)

    And in the circuit ideas on P72 Thomas Scarborough of South Africa has a circuit just for you.

    Based on 40kHz utrasounders the units could be built for about $10 apiece.
    He says

    The unit will break into oscillation when two units are 1 mete distant. Other distances can be made with more circuitry.

    You would need an electronics enthusiast for a bit of development.

    Sorry I cant post the circuit, for copyright reasons but PM me.
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