Given they're dirt cheap it was easier it just buy a DHT21 instead of messing about troubleshooting and now I have believable humidity readings. It's a little higher than I see in the body of the cellar, but the sensor is stuffed down on the floor right next to the tank of water. I plan to fit a longer lead and mount the sensor at chest height somewhere further away on the assumption it will sort this out.
For data upload I am using the Sparkfun Phant service as it's free and very easy for a microcontroller to deal with.
All I've done here is grab the data as a CSV and draw the graph in Excel, there's much more work to be done to make this readily accessible.
This is a bit of a dry run for a later project, a friend has asked me to set up some monitoring of the beehives she's setting up on a roof in London in the Spring. The interesting stats to collect are apparently internal temperature, internal humidity (may be hard due to bees messing with the sensor) and the weight of the hive. So I get to mess around building an calibrating load cells.
