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.
This power source, obtained in a 1973 publication, suggests the use of partially burned germanium...
This circuit was obtained from an Electronic Design from 1964. Transistors admit modern...
The circuit is from the 1994 National Semiconductor Linear Applications Handbook but can be...