This circuit was found in a 90s Popular Electronics. It uses an LS3404 melody chip that has several recorded melodies and that is uncommon nowadays.
This simple metronome, from 1985 documentation uses only transistors and has two settings. For...
We found this circuit in a 1988 documentation. The circuit uses a conventional complementary...
This circuit was found in a 1990 publication. The sensors are electrodes placed in the water tank...