This very low current circuit was found in the April 1995 Electronics Now magazine. The frequency should be chosen for maximum efficiency according to the small transformer used.
This circuit can be used to recognize a tone by its frequency. When this tone is present in a...
Found in a 1980s documentation, this amplifier uses an operational aplifier of the time with two...
This circuit, from a publication of the 1970s, can compare the intensity of two light sources,...