Virtual Pool, Real-world Interface


Sunday we saw robots playing pool and an augmented reality pool game. Today we’ll complete the pool trifecta: virtual pool using a real cue stick and ball in another vintage video from Hack a Day’s secret underground vault. The video is noteworthy for a couple of reasons:

First is the year it was made: 1990. There’s been much buzz lately over real-world gaming interfaces like the Nintendo Wii motion controller or Microsoft’s Project Natal. Here we’re seeing a much simpler but very effective physical interface nearly twenty years prior.

Second: the middle section of the video reveals the trick behind it all, and it turns out to be surprisingly simple. No complex sensors or computer vision algorithms; the ball’s speed and direction are calculated by an 8-bit processor and a clever arrangement of four infrared emitter/detector pairs.

The visuals may be dated, but the interface itself is ingenious and impressive even today, and the approach is easily within reach of the casual garage tinkerer. What could you make of this? Is it just a matter of time before we see a reader’s Mini-Golf Hero III game here?

9 thoughts on “Virtual Pool, Real-world Interface

  1. I played this game back in the early 90’s! They had it at Keansburg Amusement Park in New Jersey. The creepy thing is this amusement park used to be nicer, but was now on it’s way out because trains didn’t go there and people were going to better places.. such as Seaside or Point Pleasant.

    This one building had two doors opens I remember and no lights on inside. Always gave me the feeling somebody was watching or going to rape me.

    I recall this pool game and maybe 3 other games inside.

  2. Very impressive for 1990 the dedicated processor and hardware must have made these games more expensive. And what keeps the jerks at the arcade from just keeping all the cue balls or throwing them at other people? Neat games thou.

  3. Yeah – ball stealing is a pain – but people seem to cope with pool and snooker balls. You could build in a deposit function i guess – put in $5 to release the balls and $1 to play, then get your $5 back at the end if you return the ball, but you are going to put more people off playing there…

    Still pretty amazing for the time, really like it, would love one for the games room… ho hum

  4. Humm, why 4 beams?

    2 parallel beams should give you the velocity. Then, only 1 additional beam at a different angle should be enough to derive vector information.

    See, once you know the velocity, you can use that to find the unknown vector. That is, where the ball crossed the lines.

    For those of use better with pictures, think of it this way… we know how fast the ball is going and we know the time between the breaking of the diagonal beam and, say, the 2nd parallel beam. So, draw a circle with radius equal to the distance the ball could have travel in that time. Now slide the center of that circle along the 2nd parallel line until the edge touches the diagonal line. Now you have 2 points giving vector information.

    If, by chance, you built your “pool table” where the diagonal line crosses the 2nd parallel line, then you will also need to note which beam (the 2nd parallel or diagonal one) broke first as there will be two positions where the circle just touches the diagonal line.


  5. Apologies…

    We really don’t know how fast the ball is going with only 3 beams.

    That is, given only 2 parallel beams, it would take shorter for a ball to travel between them if the vector of the ball were perpendicular to the beams. But we can’t assume that.

    With 2 sets of parallel beams that are at different angles, we can get 2 velocity vectors perpendicular to the beams that we could add up to get the overall vector of the ball.

    Humm… maybe the 3 beam solution would work if we could prove a unique solution for all possible cases. But I am guessing there will be multiple solutions (possible ball paths) for a given set of beam interruption timings. An interesting problem though.

  6. Wow Wouldn’t it be nice if you could acquire one of these and replace the old screen with a new LCD one and THEN replace the 8 bit processor with a Parallax Propeller! would make for a GREAT remake

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