This harmonic oscillator controlled by crystal was found in an American documentation of the 90's. The circuit uses transistors of the time. Current equivalents can be used.
This circuit was obtained from a Linear Technology manual from the 1990s. The sensor is of the...
This circuit is from a PE Hobbyst Handbook from 1991. The integrated circuit is a common 555 and...
This traditional circuit with a neon lamp is a flip-flop that draws which of the two lamps will...