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Drag race Christmas tree

Discussion in 'Electronic Design' started by pimpom, Nov 19, 2009.

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  1. pimpom

    pimpom Guest

    A bike drag race is being formally organised for the first time
    in my state by local enthusiasts and a government department. As
    they can't afford a full set of pro equipment yet, they asked me
    if I could rig up something for them - not for free, but
    obviously at a significantly lower cost and, if necessary, with
    limited features.

    ATM, they are most concerned with the start line rather than with
    things like accurate measurement of elapsed time. Everything will
    have to be built from scratch. Commercial units are out of the
    question for now. This is not just due to cost, but also because
    we don't have easy access to the services and facilities you take
    for granted in more advanced places.

    I can't even ride a bike and what I know about what's needed is
    what I've gleaned from the internet over the past 24 hours. None
    of the organisers know all the details either. The event is to
    take place about 3 weeks from now, so I told them that I'll do
    some investigations but can't promise anything at such short
    notice.

    I may need help with the technical side if I decide to take up
    the project, but for the moment, could you please answer the
    following general questions first?

    1. Do Christmas tree light starting systems normally come
    integrated with timers and sensors for elapsed time?

    2. How much do they cost? I expect that this varies with the
    level of sophistication, but some ballpark figures will help.

    3. Are they usually standalone units or software controlled from
    a PC?
     
  2. PeterD

    PeterD Guest

    Some do come with everything, but all integrate with the system so
    that there is coordination between timing and start.
    Check Jegs, or one of the other automotive (custom/racing) supply
    houses. There are choices there.
    No, standalone. But: you could easily build one using a PC's parallel
    port and a bit of software if you are running an early version of
    Windows, or running DOS (to allow easy access to the port).

    If your PC has a game controller that is another option, but these
    have fewer ports for output.

    Even a couple of serial ports (the control lines) could be made to
    work for your needs if you don't need a big countdown. (say a single
    amber then green)
     
  3. pimpom

    pimpom Guest

    I'm thinking of something a bit more complex than simple running
    lights, and more accuracy than a 555. I /have/ been considering a
    4017, fed from a 4060 14-stage counter with a 32.768 KHz crystal
    oscillator to get the 0.5 sec countdown. Then there will be the
    detectors for position and foul starts, etc.
     
  4. pimpom

    pimpom Guest

    OK. Thanks for the reply.
    I've found out a bit more about that side of the matter.
    Portatree seems to offer low-cost solutions. But "low-cost" is
    relative and customs hassles make it impracticable to buy from
    such sources (I'm in a remote corner of India). In any case, I
    asked about prices mainly to get an idea of what's involved with
    commercial products.
    Again, that question was mainly to get a feel of how it's usualy
    done. I'm not so hot with programming and a computer-controlled
    option will still involve designing and building the external
    hardware like sensors, power supplies, lamps support structure,
    lamp drivers, etc. Given the limited amount of time available, I
    think I'll stick to a purely hardware approach.

    I've been thinking of using a crystal oscillator-counter with a 2
    Hz output - probably a 4060 - and good old 4017 decade counter,
    latched at the 4th pulse.

    There's still an important gap in my understanding of how it all
    works. The sources I've read say that the prestaging and staging
    points are detected with two beams of light, 7 inches apart, near
    the starting line. Fine, I guess I can use laser pointers and
    photosensors coupled with the countdown circuit. The gap is that
    none of the sources say how a foul start (before the green GO
    light comes on) is detected. No mention of a third beam.

    Since the staging detector beam is already cut off by the
    vehicle's front wheel before the countdown begins, I don't see
    how that can be used. Detecting the instant the front wheel
    /leaves/ the beam seems unsuitable as variations in the size and
    design of the wheel will introduce a factor of uncertainty. Can
    you or anyone else provide some enlightenment?
     
  5. pimpom

    pimpom Guest

    Puzzle solved (I think). Although I have not seen a specific
    statement to the effect, I've come across some indication that
    the time a racer leaves the starting line /is/ taken as the
    moment the front wheel leaves the staging marker beam, thereby no
    longer blocking it.

    I also read that the beam is placed about an inch above ground.
    At that height, the wheel of a car or bike would be roughly a
    foot wide. From a standing start, the time taken for a part of
    that foot-wide section to cross the beam will be an appreciable
    fraction of a second. As a point of academic interest, that's
    quite significant when reaction and elapsed times are measured to
    within a millisecond.
     
  6. Rich Grise

    Rich Grise Guest

    You don't need precision timing for the Xmas-tree, just so it's consistent
    from light to light, so the driver has a sort of countdown.

    As far as staging beams, the vehicls stops at the first beam, with some
    kind of "ready" indicator. If the vehicle interrupts the second beam
    befor the tree goes green, then it's a foul. Is there some kind of
    structure between the two lanes at start? That way you could have two
    "foul" beams, so you could tell which one fouled.

    So, press the "ready" button, the red light at the top of the tree comes
    on, and if the contestants are "staged", you're ready to go Maybe put some
    kind of interlock, so you can't start until both vehicles are "staged".
    Operator presses "Go" button, the tree counts down, and as soon as the
    green comes on, send a "start" signal to the timer at the end of the
    track. I don't know how you'd arrange for two "finish line" beams without
    something between the lanes, but when somebody wins, who cares what the
    loser's time was? ;-)

    Good Luck!
    Rich
     
  7. pimpom

    pimpom Guest

    According to what I've learned these past few days, even *that*
    is still not quite correct. Going past the first beam before the
    start (called "deep staging") is usually allowed, but it carries
    the risk of also going past the second beam and being
    disqualified.
     
  8. Frank Buss

    Frank Buss Guest

    If you have a parcel service like UPS, I think Digikey will deliver parts,
    but other shops can deliver full systems, too, if there are no export
    restrictions to your place.
    3 weeks is not much time for building a professional system. The low-cost
    solution: Some switches, some lamps and a human operator (someone sitting
    beside the start line and switching the switches while watching for false
    starts :)
     
  9. pimpom

    pimpom Guest

    Thanks for your interest, but no way is that possible. In this
    remote place - really the most isolated state in India - I can't
    even get things shipped quickly from another state.
    It's an interesting project but the short time available is
    frustrating, especially since I've never anything similar to this
    before. But the fully manual option is just not acceptable (I
    assume the suggestion was made tongue-in-cheek :)). They might
    just as well count 1-2-3 with a megaphone.
     
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