This circuit from the 90s, found in an Electronic Engineering can be used as a shield since its control is digital with TTL logic of 5 V. The components used are still common today.
This simple metal detector was found in a 1960 Sylvania transistor manual. The phone must be high...
This is one of the many versions of this type of indicator that the reader can find on our...
Found in an English publication from the 1980s, this circuit can be built with equivalent...