Making the ball traps
The next step is to enable the ball bearing to make an electrical contact between two points. This is a bit harder than you might think. The ball is a sphere and only makes contact with a surface at one point. If you want it to bridge two conductors, they have to be very close. The solution is to use a raised wall for one contact and a conducting strip for the other. For this task, we need self-adhesive copper strip (foil). It is sold by the reel in hobby shops for making Tiffany-style stained glass and also by electronics suppliers for radio frequency (RF) screening. You can get it in various widths; we used a 5mm (1/4") wide strip. Figure 15-17 shows how this foil can be used to make a detector or trap for the ball.
Figure 15-16: Attaching the two pillars to the playing surface.
See how the ball is forced against the corner of the wall and at the same time makes point contact with the foil on the playing surface? On the playing surface, first drill and countersink a 2.5mm (1/8") hole, and then lay the foil over the top and smooth it down. You will see the indentation of the countersink hole. Take a sharp pencil and make a hole in the foil. Gradually make it larger and then put the countersunk bolt into the hole and tighten up a nut on the other side. This pulls the foil into the countersink and make a good electrical contact. It’s a good idea to make the ...