This project is built to monitors the instantaneous current, voltage, frequency, and real power consumption in home. To monitor voltage, the project uses a dedicated miniature transformer. Current is measured using a home built current transformer that clamps around the incoming power feed. The current transformers are homemade from split ferrite cores with 100 turns into a 0.1 ohm ‘burden’ resistor. The real power is calculated with an analog multiplier followed by a low pass filter to obtain the DC component (real power).
These analog quantities are then fed to a 12-bit A/D converter driven by a ’77 PIC. The circuit gain give resolution of 5 Watts. As a result you can even see the effect of turning on one lamp. Power usage monitor is designed by Edward Cheung.