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.
This circuit simulates an inductor. Or operational amplifier of old type, but a configuration is...
We found this circuit in a 1967 Electronic Design. The circuit uses contemporary transistors that...
To control relays safely with double insulation, we suggest the circuit in the figure. The optical...