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 was indicated in an old American publication to serve as a Laser alarm system as a...
This circuit, which uses only transistors as active components, was found in a 1987 documentation. The...
This sound meter or sonometer was found in a Popular Electronics from the 80's. The circuit can be...