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 small automotive NiCad battery charger uses only passive components and has the number of...
This circuit was found in a 1987 edition of the United States' Hands On Electronics magazine. The...
This 20 Hz high-pass filter was obtained in a 1965 American publication. The operational amplifier must...