I have a clear plastic ball with some electronics inside. When bounced, LEDs flash on and off. I suspect that it contains a piezoelectric crystal and I would love to know how it operates.
Vincent B. Maier
Actually the 'flash-when-bounced' ball works on a much simple principle than what you suspected. I happened to have one of these balls at home so I took some photos for you - picture is worth a thousand words. So here it is:
When you bounce the ball spring starts vibrating and in most cases it touches the middle rod. This establishes the contact that the microchip starts flashing the LEDs.
- is the ball from far,
- zoom into the electronics inside the ball. One can see the microchip and battery at the bottom and to the left, transparent domed thing is a LED (Light Emitting Diode) at the middle top and the activation spring on the upper right.
- zoom into the activation mechanism: basically one end of the contact switch is just a loose spring with another contact being a rigid rod in the middle of the spring.
Other activation mechanisms are also possible. Two metal disks separated by a slight gap and mounted on the flexible holders are another configuration (suggested by Paul Walorski).
Piezoelectric crystal (material that produces potential difference as a result of applied mechanical stress) could be used for this purpose too, however, generally it is not used due to high cost.
Anton Skorucak, M.S. Physics, Founder of PhysLink.com