Diagram Of The Basic Layout Of Catadioptric Telescope Where Can I Find A Basic Circuit Diagram For A Switch That Uses A Hall Effect Transistor?

Where can I find a basic circuit diagram for a switch that uses a hall effect transistor? - diagram of the basic layout of catadioptric telescope

A schematic and parts list would be nice too. You need only one transistor to an alarm control switch, LED or piezoelectric. Simple is better.