Found in the 1990 special issue of Radio Electronics Experimenter magazine, this circuit uses an automobile ignition coil. Adjustments can be made to suit the coil.
This interesting comparator circuit was found in an old Motorola documentation. The integrated circuit...
We found this circuit in a 1995 paper. The reed switches are surrounded by a few coils of coarse...
This circuit was obtained in a 1990 documentation and can be powered by the previous circuit...