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Radio direction finding for robots

Discussion in 'General Electronics' started by Dingo, Aug 30, 2004.

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  1. Dingo

    Dingo Guest

    Hi group,

    I want to have a smallish robot (20 - 30 cm long) accurately detect the
    direction 2 or more FM radio beacons are in relation to it. I have found
    very little googling for it. Does anyone have a curcuit for a reliable and
    accurate (as possible) radio direction finder? Or a "bug" finder that shows

    I am quite surprised not many other people have tried to determine position
    of a robot via radio direction finding.

  2. Ken Taylor

    Ken Taylor Guest

    The search terms 'direction finding' and 'led' brought up suitable
    responses. A Doppler direction finder with LED display is what you want,
    although they generally aren't particularly accurate, and antenna sizing is
    going to be a problem. They would however interface easily to a parallel
    buss. DSE had a kit; Jaycar may still have it.

  3. The old EA project was discontinued long ago, although back issues of
    the article are still available via Silicon Chip.
    As Ken said, antenna sizing will be a major problem (and quite
    possibly entirely impractical) for a small robot.
    If memory serves me correctly, me EA project suggested antenna on all
    four corners of a car, and even then the accuracy wasn't that great.
    Do you have to use RF direction finding?
    What sort of range and resolution are you after?, if your resolution
    is a couple of meters minimum and your robot will be used outdoors
    then GPS may be a neat solution.

    Dave :)
  4. Dingo

    Dingo Guest

    I merely wish to know the location fo my robot within a few rooms in my
    house. I would like it to plot itself as accurately as possible within a
    couple of rooms. Odemetery would probably be too sloppy in a normal house
    environment where lots of turns are need to avoid unexpected obstacles and
    lots of different types of surfaces and my lack of sourcing the right sized
    stepper motors.

    I won't have line of sight so IR beacons won't work.

    Basically if I had three known location beacons and could find the direction
    to them from my robot then the robot could offload the processing to a pc to
    do the Trig and plotting of location on a known map.

    I was thinking "FM Bug" detectors or similar would be usefull (ie pretend
    the beacons are bugs) it all comes down to accuracy.

    I don't know about radio but with FM if you had two antenna spinning around
    a central axis. Couldn't you "catch" the two points during 360 degrees of
    rotation where the signal was strongest or most in phase? then at least you
    could draw one line on a map. Then just repeat with different beacons.

    Sorry for the long post :)

  5. Ken Taylor

    Ken Taylor Guest

    Well, if you're happy to put moving parts onto your robot, how about making
    it a cylinder with a slot in it, rotated by a stepper motor (so you can
    accurately determine where you're 'pointing'). Inside the cylinder is your
    antenna, just a length of wire, essentially. Rotate the hole in the
    cylinder, which otherwise shields the antenna (clue: make the cylinder
    something RF shielding :) and determine direction of max signal strength.
    If you have two receivers (or selectable channels) you can seek different
    beacons on different frequencies. Trig, etc is 'just computation'. I leave
    the trivial details to your good self. :)


  6. I'm no expert on RF or direction finding, but I think this most likely
    isn't practical within the size of a room. The wavelegth of FM is
    about 3 meters, and you'll probably have all sorts of issues with
    multi-path distortion etc.

    What about using say ultrasonics to measure the distance of your robot
    from various objects/walls around it? With an inbuilt electronic
    compass you can know which direction your robot is pointing, and if
    you know the distance to each object in certain directions then it
    should be possible to calculate the robots position based on a
    predefined "map" of the room.
    Ultrasonic sensors can be very accurate.

    Dave :)
  7. Dingo

    Dingo Guest

    Yeah - everyone seems to use ultrasonics - I've just found them to be picky
    about hard/soft materials they bounce pings off.

    I figure if there exists a curcuit to measure radio signal strength then why
    couldn't I have a highly directional antenna spin in 360 degrees taking
    measurements every so often and report in which direction it found the
    strongest signal.

    I only wish to plot the location in two dimensions.

  8. AnyBody43

    AnyBody43 Guest


    I am no expert however I have hears and seen a few things.

    Decca Navigator (UK + few others) and Loran (everywhere else)
    use the phase difference between signals to locate the position.

    Tracker (UK) service for tracking (stolen?) vehicles seems to
    have 4 antennas on the top of some (many) UK police cars. They
    are just 1/2 metre sticks about 1 metre, or less, apart arranged
    in a square. thay have not been observed to rotate :)))

    In aviation, the control tower can get an instant bearing of a
    sending aeroplane with every transmission.


    I don't think that you need moving antenna. If you have two
    antennas and measure the phase difference between them you can
    get a line or pair of lines? or more? (sorry too hard for me)
    that describe the position of the Tx. With more antennas you can
    get more info. I guess that 4 is the minimum for a bearing
    otherwise they would have less than 4 on the police car.
    Hmm not the same thing but maybe interesting.
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