Anyone who has ever wound a toroidal coil by hand can tell you ... of windings and their spread on the form. lacking a ferrite core for testing, [Sandeep] used a plywood ring as a stand-in ...

This probe design is little more than a 3D printed case, an old power supply toroid, and a conventional alligator clamp to make the business end. The sensor uses a ferrite core and a hall effect ...