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.

Rocket Altimeter (CB25357E)
Today we have more compact solutions. This is from a Radio Electronics magazine from October 1990....
Band rejector active filter (CB7405E)
This filter was found in Texas Instruments documentation from the 1980s. The circuit uses a common...
Transistor test (CB22545E)
16 commercial test circuit for tubes and transistors appeared in Radio Electronics magazine in...