This very simple circuit uses a phototransistor and a very sensitive relay (reed type) being used over short distances with a lens system. The circuit is from a 1967 Japanese publication.
This normally open, two-terminal, high-sensitivity circuit was found in General Electric's...
Bubba's oscillator, shown in the figure, is another type of phase shift oscillator, but it takes...
This sensitive electroscope uses a MOSFET 3N128 and can detect electrostatic charges of objects....