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Although products are becoming more and more available for monitoring your home power usage, I'm one of those idiots who can't leave well enough alone and who would rather shell out $100 and hours of my time in order to save $20 and learn something in the process. Building on the fine work of Trystan Lea and others at OpenEnergyMonitor.org as well as various and sundry web sources and acquaintances the result is a self-contained Arduino shield for monitoring the energy usage of your home using clamp on current transformers, an ethernet shield, and an Arduino. The resulting Energy Monitoring Shield has a built in switching power supply and with mains voltage (120VAC in the US) to the board can do power factor correction as well. With mains voltage to the board it is also more dangerous than your typical home electronics project and as such has been rejected for distribution by commercial maker outlets like adafruit and sparkfun.
A thermocouple datalogger based on the Arduino platform & (previously, rolling your own thermocouples )…
Abstract: I picked up a cheap RGB LED from RadioShack (276-028) on my way home from school/work yesterday.