Based on the LF256 operational amplifier, this circuit was found in the September 1989 issue of Radio Electronics magazine. The indicator is analog, and the power supply must be symmetrical.
This conventional circuit uses the 4017 to control incandescent lamps or LEDs, according to...
This circuit was found in the September 1993 Electronics Now magazine. It is based on the 555 and...
This interesting circuit with a neon lamp and a transistor was found in Radio Electronics magazine...