This circuit was found in Electronics Today International of the 80's. The circuit uses still common components, providing the indication through LEDs.
A bridge with greater sensitivity and, therefore, lower consumption for the microcontroller...
LTC7841 PolyPhase® Synchronized Boost Controllers Mouser Announces Analog Devices LTC7841...
This sinusoidal oscillator was found in Radio Electronics in 1989. It uses a 741, but other...