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 circuit was published in a 1977 English magazine 1977, but it can be easily assembled since...
In this circuit the voltage across the LED is limited by the diodes. The maximum current also...
This circuit, using a unijunction transistor (UJT), converts a voltage applied to the input in a...