This Harmonic Distortion Meter designed for measuring the quality of AC supply. The meter is built with a PIC18F2550 and the full wave rectifier front-end circuit. The input signal to the 10-bit ADC is full wave rectified. For safety, the AC power line, 220VAC is measured through the step down isolation transformer. But, the meter can be applied for high voltage application with the appropriate signal conditioning.
The software performs DFT calculation finding the amplitude of the fundamental frequency and the 3rd harmonic. The distortion is computed by the ratio of the amplitude of the 3rd harmonic to the fundamental frequency. The meter has been tested with the square wave signal resulting 33% distortion. For low voltage AC utility, 220V, the reading showed approx. 3%.
Project Documentation and Schematic