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Who gets there first!

Discussion in 'General Electronics Discussion' started by superheterodyne, Aug 2, 2017.

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  1. superheterodyne


    Aug 2, 2017
    Hello all guru's, I hope you might be able to help me out?

    I've been given the task of building/buying a circuit that is able to indicate who can reach the top speed in a static bicycle pedalling race.
    The premise is simple enough; three cyclists mount their respective bikes and pedal like fury!

    The person reaching a/the desired speed will light an L.E.D or something similar indicating their winning the "race"

    I have no idea where to start with this conundrum. I have a feeling this request may have to be turned down!!!

    Any thoughts?

  2. BobK


    Jan 5, 2010
    That is an odd kind of contest. A stationary bike, (at least the ones I have tried) do not have that much inertia. The time to reach top speed would likely be no more than a few seconds, maybe even less than a second.

  3. kellys_eye


    Jun 25, 2010
    Connect a simple generator to the driven wheel. Measure the voltage output and feed it to a comparator.

    When the speed reaches a preset point it can be arranged to light a lamp (and lockout the other bikes from triggering it).
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    I would measure the frequency. There are several analog ways of doing that.

    The main issue is component tolerances, because these may cause one circuit to read higher than the other.

    A digital circuit that waits until it sees more than a certain number of pulses in a given time (most easily accomplished by measuring the time between pulses and looking for a period of time in which no period between pulses is greater than 1/f (where f is the frequency corresponding to the target speed)
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    On second thoughts, a race to a specific distance makes more sense. That way you simply count revolutions of the wheel and see who gets to a particular count first.
    kellys_eye likes this.
  6. AnalogKid


    Jun 10, 2015
    I agree with Bob; the race as described would be very short. But if that really is the thing, then a tach sensor on each bike, three level comparators, and a 3-input game show circuit to latch the winner.

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