This circuit was found in a 1981 documentation. As you can see, this is a well-designed automatic scoreboard for Foosball games, in which the passage of the ball through the drawer channel after each goal changes the number of the display. Of course, for a normal application, two units like this must be mounted, installing their sensors, one at the passing of each goal. The author suggests that behind each goal there is a tube through which the ball passes when falling, and in this tube the sensor would be installed, an LDR that would be illuminated by a small lamp. The passage of the ball, interrupting the beam of light would trigger the circuit with the change of score. Of course, imaginative readers will have other alternatives for installing the scoreboard and may even be able to use it in other games or even counting objects, remembering that the use of a single display limits its capacity to values from 0 to 9.
