This project uses Atmega168 microcontroller to compute the power usage at home and logs it to an SD card. It has a graphical LCD display too that shows the power usage as a strip chart. Besides, the voltage and current waveforms can also be displayed on the LCD.
The current is measured using a pair of current transformers whereas the voltage is measured using a 2000:1 voltage divider network. An LMC6484AIN quad op-amp and an AD623AN instrumentation amplifier are also used for signal amplification from the current sensor and the voltage divider.
For more detail: Power usage monitor using Atmel AVR using Atmega168 microcontroller