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.
We found this oscillator in an old documentation. The crystal frequency can be different to get...
This circuit is from an old publication from 1977 and can be implemented with more modern...
The circuit in the figure produces a perfectly rectangular waveform signal. For a 1 nF C1...