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 oscillator for the practice of telegraphy provides a good sound in a loudspeaker, with only...
This ultrasonic insect repellent was found in American documentation from the 1980s. The...
The short-wired circuit is suggested by National Semiconductor in documentation on the LM3909. The power...