This circuit was found in a 90s American publication. The same configuration appears in several places on this site, obtained from different sources. The lamps can be replaced by LEDs.
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...