The digital dehumidifiers usually have a regulated 5 VDC and/or 12VDC rail, as well as an unregulated low voltage source,on the control bosrd, that you can tap into to run a developer board. They also have a relay driver chip that is connected to all the parts that need to be switched. An arduino stamp can be "jumped" into various points of the existing control board without many extra parts at all. I've detailed this procedure in previous threads. It's kinda fun!
Here's one:
http://ecorenovator.org/forum/geothe...-window-c.html