This circuit is from a Popular Electronics from the 90s. It uses an opto-coupler with SCR directly controlling a 20 mA current load.
This circuit was obtained in a 1980 Hobby Electronics magazine. It is a digital slot machine using...
This circuit with the PLL4046 was found in the October 1994 Electronics Now magazine. The...
This resistive sensor was found in a 1969 US documentation. The circuit uses transistors of the...