This circuit was obtained in a 1982 English magazine. The purpose of this circuit is to interface signals other than TTL circuits with TTL inputs. The transistor can be a BC548, 2N2222 or any equivalent.
This configuration appears elsewhere on this site. This is from a 90’s Popular Electronics and is valid for...
This circuit is from an Electronics World of 1968. The transistors are of the time and the power...
An way to change the frequency of the previous oscillator (CIR112E) is to add a variable capacitor in the...