Dew point detector:
I just got my Arduino talking to my $2 China Temp/Humidity sensor. The software reports temp, relative humidity and calculates dew point. One of the big problems in my shop/garage is keeping my machines from rusting. When the temperature falls below the dew point water condenses. When that happens on iron/steel it rusts. I'll be raising a digital output on my Arduino when the temperature comes close to falling below the dew point. I'll lower that digital output when the temperature rises somewhat above the dew point. That digital output will control a solid state relay to turn on/off a space heater or heat tape under a shroud/tarp covering my equipment. Using this, I still won't have to heat my shop/garage but I won't have to scrub rust off my equipment as often.