[Willem] has been using an Arduino to monitor temperatures and electricity usage. For the temperature monitoring he picked up some 1-wire temperature sensors similar to those we’ve featured in the past. To pick up on electricity usage he’s not using an amp sensors, but because he’s in the UK he does have a flashing LED on his power meter. There’s a known trick to pick up these flashes with a photo cell to calculate energy usage based on meter readings. Finally, the data from the three sensors (indoor temp, outdoor temp, and energy usage) is piped over the Internet via an Ethernet shield so that it can be collected and graphed.

[Willem] has had the system running for a year. If you’re nosy you can look at the temperature graph generated from his collected data.