This circuit was obtained in an old Elektor and can be adapted to use white power LEDs. The transistor must be equipped with a heat sink. The circuit has a battery charger.
Found in a Popular Electronics from the 1990s, this circuit uses components from National...
This detector is from the 1990 Motorola Dataar Databook, but can be adapted to work with more...
This two competitor version of the game is shown below and uses lamps as indicators. You can...