This circuit was obtained in a French documentation from 1981 and can be easily assembled. The analog instrument itself can be replaced by the current scale of an ordinary multimeter.
This circuit was found in a 1977 publication, but it can be easily assembled, although unijunction...
This circuit produces an intermittent ring tone being triggered directly by the telephone line. However,...
This 20 MHz bandwidth circuit was suggested by the National Semiconductor in 1970 documentation. Modern...