Found in a Popular Electronics from the 90's, this circuit detects the approach of objects by the reflection of the radiation emitted by the LED. The relay is a 12 V sensitive type.
This circuit was found in a 1980s Intersil documentation. The integrated circuit used is not...
Although it is a common configuration today, these circuits were taken from an old publication. The...
This circuit, from an old publication, can also use modern transistors. Note that the unit is...