This power step for relay activation was found in the 1964 RCA transistors manual. The circuit is of the NF type and the transistors admit equivalents. R4 depends on the drive voltage.
This shield circuit uses a common CMOS port. The voltage depends on the interfaced logic. The...
This circuit was published in Popular Electronics from the 90's. The components are common, as...
This circuit with SCR was found in an old documentation. The SCR can be the TIC106, and the...