Optical sensor for PC (CB20548E)

This circuit was found in a PC documentation from 1996. It can be used as a shield with modern microcontrollers.

230 to 2.8 kHz Adjustable High Pass Filter (CB12571E)
The cut-off frequency of the filter shown in the figure can be adjusted to values between...
Burglar alarm (CB7428E)
This circuit was found in a Popular Electronics from the 90s. The components used are all common...
MOSFET RF Oscillator (CB19562E)
This circuit uses a dual floodgate MOSFET not very easy to obtain today. Its handling is very...