HackaHouse - [Paul] was pretty sure that he and his family used a lot of electricity throughout the day 
. Admittedly, he enjoys his creature comforts, but was wiling to try living a little gre ener. The problem was, he had no idea how much electricity he was using at a given time.
. Admittedly, he enjoys his creature comforts, but was wiling to try living a little gre ener. The problem was, he had no idea how much electricity he was using at a given time. While some power companies offer devices allowing homeowners to monitor their energy usage, [Paul’s] did not. After a bit of research however, he was ready to build a power monitoring system of his own. He found that his meter emits a small infrared pulse every time a watt-hour of electricity is consumed, so his system counts how many flashes occur to measure usage.
The counting circuit is pretty simple consisting of only an AVR, a resistor, a capacitor, and a phototransistor. The data is fed to a computer where the results are graphed with gnuplot.
It’s quite a useful little hack, and undoubtedly far cheaper than purchasing a whole house power monitor.