+ Post New Thread
Results 1 to 6 of 6
  1. #1
    Newbie level 3
    Points: 23, Level: 1

    Join Date
    Jan 2016
    Posts
    3
    Helped
    0 / 0
    Points
    23
    Level
    1

    Am creating a game that requires a simple magnetic field sensor....

    I have been tasked with creating a game for a charity event.

    The game is, essentially, shooting a Nerf dart through an 8" hole approximately 12' away from the shooter.

    I want to install tiny neodymium supermagnets in the tips of the darts and, when they pass through the hole in the target and strike the backboard, set off a siren and flashing lights.

    Thus far I have not been able to nail down a simple but sensitive enough design that will act as a trigger for the sound and lights. I understand a copper coil would be required to boost the sensitivity, but cannot seem to find anything that does not power a set of headphones.

    Any ideas out there?

    Thank you,

    Cent13

    •   AltAdvertisement

        
       

  2. #2
    Advanced Member level 5
    Points: 40,508, Level: 49

    Join Date
    Mar 2008
    Location
    USA
    Posts
    6,531
    Helped
    1919 / 1919
    Points
    40,508
    Level
    49

    Re: Am creating a game that requires a simple magnetic field sensor....

    First, why magnetic rather than (say) a set of optical beams
    where interrupting any one of them, rings your bell? Is the
    goal a functioning game, or is it to explore this particular idea?
    You might be able to get even simpler if the Nerf dart has any
    decent momentum remaining, like a suspended screen that is
    made to contact a back comductive plate and close the circuit,
    but hangs short of that at rest.

    Magnet to induce meaningful current in a large coil, will have
    to move fairly fast. I suspect a Nerf dart is not very.

    You would have to apply some gain and likely some noise
    rejection (ambient 60Hz hum is likely bigger than your slow
    flying magnet's input, because it will fill the coil area while
    the magnet is a tiny fraction making a tiny blip).

    If time is your enemy then simplicity is your friend.



    •   AltAdvertisement

        
       

  3. #3
    Newbie level 3
    Points: 23, Level: 1

    Join Date
    Jan 2016
    Posts
    3
    Helped
    0 / 0
    Points
    23
    Level
    1

    Re: Am creating a game that requires a simple magnetic field sensor....

    Dick,

    This is not attempting to create a meaninful current. It's just a circuit that detects when a magnet is near and sends a trigger pulse to a 555 timer.

    https://www.reddit.com/r/Nerf/commen...ronic_scoring/

    Someone has already done it. While there doesn't appear to be enough demand to fund their Kickstarter project, the fact remains that they did it and I think I can do it, too.

    Regards,

    Steve



    •   AltAdvertisement

        
       

  4. #4
    Super Moderator
    Points: 53,524, Level: 56

    Join Date
    Apr 2011
    Location
    Minneapolis, Minnesota, USA
    Posts
    13,062
    Helped
    2604 / 2604
    Points
    53,524
    Level
    56

    Re: Am creating a game that requires a simple magnetic field sensor....

    I have played with neodymium magnets and coils of wire. Your idea is good but I find they need to be very close together, in order for a passing magnet to induce current in the coil.

    At a distance of 4 to 8 inches, I don't think you'll see much response.

    And then what if the dart hits only the rim of the 8" hole, but doesn't go in? Wouldn't the magnet impact as close (or closer) to the coil as it would when the dart goes through the center of the hole? Therefore counting incorrectly as a score?

    Besides recommendations in post #2, I think a photosensor would work for you.

    - - - Updated - - -

    Now I see dick_freebird mentions optical beams (which implies an optical sensor) in his post. I believe the dart flying past will alter the light falling on the sensor, so you can detect it a few inches away.



  5. #5
    Newbie level 3
    Points: 23, Level: 1

    Join Date
    Jan 2016
    Posts
    3
    Helped
    0 / 0
    Points
    23
    Level
    1

    Re: Am creating a game that requires a simple magnetic field sensor....

    If you take a look at the provided link, it leads you to the demo video at the Kickstarter site.

    That video clearly shows a tiny magnet being inserted in the dart tip, then dropped tip-first onto the sensor plate, which responds with a flashing light and signal. That's what I am shooting for. Is there any way of duplicating that feat? I want the dart, having made it through the 8" hole, to strike a similar plate set six inches back from the hole and set off the 'jackpot' alarm and lights.



    •   AltAdvertisement

        
       

  6. #6
    Super Moderator
    Points: 53,524, Level: 56

    Join Date
    Apr 2011
    Location
    Minneapolis, Minnesota, USA
    Posts
    13,062
    Helped
    2604 / 2604
    Points
    53,524
    Level
    56

    Re: Am creating a game that requires a simple magnetic field sensor....

    It's now clear what you want to do. The magnet hits a plate which is a few inches in diameter. This ought to be detectable by a sensor of some kind, to trigger a 555 timer. It may be amplified by a transistor or op amp.

    One obvious tactic is to place two metal plates very close, held apart by very loose non-metallic springs. A dart impact causes the plates to touch. The tricky part is to make them large enough, and sturdy enough, to maintain a hair's breadth between the plates, yet touch together when a lightweight dart hits it. Then they must bounce back into position reliably.

    I think the easy and reliable sensor will be a small speaker glued to the back of a large cardboard. It generates voltage just like a microphone.

    - - - Updated - - -

    If you use an acoustic sensor, you won't need to embed a magnet in the dart.



--[[ ]]--