Metal detector receiver (CB22457E)

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

Shield for MSX (CB18698E)
If the reader has an old MSX still working, it can be used as a microcontroller for your robotics...
Locator transmitter (CB8729E)
This circuit was found in a 1993 Electronics Hobbyst Handbook. The circuit operates in the FM...
SCR Simulator (CB16615E)
In the figure we have the way to simulate an SCR using two complementary general-purpose...