This proximity sensor was found in a 90s Popular Electronics. The base is a PLL567 that operates at around 100 kHz. The circuit operates by capacitance sensing.
The circuit shown is from an old European publication. In it we have the way to activate a relay...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in an American documentation and can be added to common amplifiers of any...