Found in a 90s Popular Electronics, this sensor operates by infrared reflection. The components are modern, and the phototransistor can be of almost any type.
Found in a documentation for radio amateurs from the 90s, this circuit is suitable for RF...
This circuit found in the February 1992 issue of Radio Electronics magazine is designed to adapt an...
This traditional version of a double time constant dimmer using triac is from the 90s...