This primitive solar radio was found in a Gernsback publication from 1960. The transistor is made of germanium of the time and the earphone is magnetic with high impedance.
This FM detector circuit was found in a 1977 documentation. The circuit uses a 1977 Signetics...
This very simple circuit turns on an LED when an object interrupts the light that falls on the...
This 1970 Philips circuit uses a mechanical counter. The circuit is triggered by a reed switch...