This Schmitt trigger was found in old documentation. The transistors can be of the general-purpose type like BC548 or even 2N2222.
Found in a publication by Gernsback from 1960, this circuit makes use of germanium transistors of the time....
To control relays or DC motors safely with double isolation via the parallel port, we suggest the...
This circuit is from a 1975 Sperimentare (number 11). The circuit uses optical coupling for a...