Metal detector receiver (CB22457E)

Found at Popular Electronics this receiver is used with a transmitter for quadrature-coil signals.

CMOS 4001 Crystal Oscillator (CB888E)
Frequencies up to 5 MHz can be poroduced by this circuit. The output is a square wave signal. The...
Parallel Switch Indicator (CB17218E)
This circuit monitors the activation of a lamp or other load through parallel or two-way switches. The...
Emergency light (CB7044E)
This circuit was obtained in an old Elektor and can be adapted to use white power LEDs. The...