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 simple circuit for a high impedance magnetic phone (500 ohms or more) has been found in a...
This 3 V rail to rail buffer was found in a National Semiconductor documentation. The gain is unit....
We found this circuit in the September 1971 issue of Radio Electronics magazine. The sensor is an...