Found in Popular Electronics from the 90s, this circuit uses a reed switch on the rails as a sensor. Instead of lamps, in a modern version, LEDs can be used.
This sound effect circuit was obtained from an article in the April 1969 issue of Radio...
Found in a 1990 Electronics Handbook, this circuit causes an LED to flash when the phototransistor receives...
Found in the May 1997 issue of Electronics Now, this circuit produces a variety of sound effects for...