Which sensor is best? (Motion detection)

Discussion in 'The Projects Forum' started by brianllama150, Dec 1, 2008.

  1. brianllama150

    Thread Starter Member

    Nov 6, 2008
    12
    0
    Hi everybody, I've been lurking a while and decided I'm in need of my own topic.

    I have a project involving a game table (Beer pong/beirut) and am in need of a motion detection system for when the ball goes into the cup. This will eventually trigger lights in celebration, but this topic will be simply about the sensors.

    If you do not know what beirut or beer pong is or how to play, and would still like to help, then thank you very very much and watch this to understand it: http://www.youtube.com/watch?v=HQdhF9AaZ6s (While I don't agree with the rules, you get the jist of it)

    So my table will be glass and I plan on having to modify the cups either cosmeticly or electronicly or both. I will be having water in the cups instead of beer, so remember that in terms of sensors.

    At first I planned on having the bottoms of the cups clear and painting the rest of the cup and putting a PIR sensor underneath. The motion of the ball landing in the cup would ideally trigger the sensor. Surely I'd have to lower find the right sensitivity as to avoid false positives with hands over the cups. My friend told me this wouldn't be good because it'd have to go through the water in the cup (refraction might be a problem) and the ping pong ball wouldn't be have a high enough temperature difference to trip it. Do you all concur or it possible?

    We then thought of photodection, like the technology in garage door obstruction sensors or convenience store customer sensors in the doors. The setup would look like this: http://cantaloupearmy.com/random/sensors.jpg
    The we would modify the cups as follows: Install sensors on the sides of the cups at potential ball level, hook the leads up to magnets at the bottom of the cup. Hook the power leads to magnets in the glass, so that when the cup is put in place, the sensors are powered. The magnets would be there to keep cup in place so that the circuit would be complete. Questions on this one: Can magnets carry charges? What type of sensors do I need? (Cheapest possible, considering we need 20 of them)

    Then we thought of light difference sensors. This setup would be like this: http://cantaloupearmy.com/random/sensors2.jpg With the shadow of the ball while in the cup, the sensor would notice the change in light. This, too, would be susceptible to false positives without LEDs halfway down the cups pointing down towards the light sensor. Question remainds, whether we're right in thinking magnets would carry a charge.

    Do any of these ideas sound promising? We had other ideas but these seemed best to us, assuming we could modify the cups in a discrete and non game-changing manner.

    If the emitter and receiver idea would work, please let me know which type of sensors/diodes I need to buy because I am at a loss of knowledge in that area.

    Any questions will be immediately answered, because I really would like some help on this project as soon as possible. Thanks everyone!
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    LEDs / Light Sensors perhaps?
     
  3. brianllama150

    Thread Starter Member

    Nov 6, 2008
    12
    0
    Why do you say that? Do you just like it the best? haha
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    If the balls are colored or opaque, the idea of a light sensor in the bottom of the cup is the easiest way to go. The change in illumination with a ball in the cup would be easily detected. You might want to have a light source over the cups.

    It's a lot less elaborate than paired emitters/sensors.
     
  5. brianllama150

    Thread Starter Member

    Nov 6, 2008
    12
    0
    Right, but a light source above the cups would then enable hands across the cups (Which happens alot) to cast shadows. So I figure I'd need to put the light source within the cups, but above the potential ball area. Is this still the best way to go or did you consider it the best only because you didn't foresee modification of the cup?
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Well, once the hands are removed, the only thing blocking light is the ball. I'm a bit past playing beer pong, so I'm not up on the scoring speed. If it has to be immediate, then breaking a light beam in the cup is going to be best.
     
  7. brianllama150

    Thread Starter Member

    Nov 6, 2008
    12
    0
    I suppose it comes down to cost. Do you know what type of transmitter/receiver would I need to use the 2nd idea? (Breaking a light beam opens up circuit)
     
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