This circuit is from American documentation from the 1980s. The circuit can make use of any common NPN transistor and the power comes from two small batteries.
This circuit with low impedance output and 900k input impedance was found in the October 1993...
This oscillator for Morse code training was found in a Popular Electronics from the 90s. The...
This is another one of the many debouncer circuits that the reader can find on this site, and it...