We found this circuit in the August 1994 issue of Electronics Now magazine. The circuit is based on the now uncommon CMOS 4046. The frequency range is given by C1.
This circuit is from a 1974 publication, but it can still be easily assembled today with BC548...
Found on Popular Electronics in the 1980s, this circuit detects a change in air pressure using a...
This 3-transistor amplifier stage was found in documentation from 1963. The transistors are made...