Reader [john] finished up his home power monitor over the holiday weekend. It uses a pair of current transducers clamped onto the mains. These output 0-3V and are read by the Arduino’s ADC. The Arduino averages samples over a 20 second period, calculates power used, and uploads it using an Ethernet Shield. The shield can’t do DNS lookups, so he uses a WRT54G to negotiate with the remote webserver. He admits that the system could be more accurate; it can’t detect small loads like wall warts. He also says that money could be saved by talking serial to the router instead of over ethernet. Here are the current usage charts.

You can find many power monitor projects like this in out Home Hacks category.

Arduino has just released an official ethernet shield. It’s based on the same WizNet W5100 chip that was used in the tiny ethernet board we covered earlier. The W5100 handles the full IP stack and can do TCP or UDP with four simultaneous sockets. The board has a power indicator plus six LEDs to debug the connection. It works with the standard ethernet library. The reset button resets the shield and the Arduino. The SD adapter is not currently supported by the Arduino software.