This oscillator that generates signals below the audible range (sub audio or infrasound) was found in a 1965 documentation. Transistors are for general use.
This heartbeat sensor circuit was found in the July 1992 issue of Radio Electronics magazine. The...
This amplifier circuit with a low power MOSFET was found in Popular Electronics from the 90s. The...
This circuit, which can be built with several CMOS gates, was found in the March 1996 issue of...