wo wo wo... those relay boards from sparkfun are not meant to actually control that much power. You will start a fire. The traces on those boards is way too small to handle even 3a. they are fine for a trigger chord for a bigger relay box (like MLC or titan Helios), but not to put a 5a dehumidifier on. If you want to use those relays, put them directly on the wire, not on small traces on a dc board. I use some I was able to pick up for cheap (crydom d2425) straight out of arduino (internal opto-isolation). they will flip with 3.3 too, and handle 25a. So running my 5a dehumidifier (with a 12a peak when compressor kicks in) doesn't even need a heatsink in the junction box the relay is in.
my system is using ds18B20 Dallas OneWire temp sensors , DHT-22 humidity sensors, and 5 25a relays. Everything is triggered from my control software I have written in c++ using boost libs for serial. so arduino sits there listening on serial and when it gets a line, it parses the command and switches to what it needs to do.
I am waiting to order my xBee parts due to the flooding in Tiawan a while back. the costs have gone up over twice what they were in Augest, so hopefully xBee modules will become cheaper soon.
Would love to join forces, as this has become my main project the past month. I havent gotten on these forums for quite some time, and it would be good to get involved in the community again instead of sitting in my basement 14hrs a day making things alone for myself..
I also have a bunch of scripts to go with motion, for multicam security motion detection, for starting reggea music 5 seconds after the door is open, also upload all still images and video to offsite sftp server as they are created.
I am hoping to port all of my project onto a beaglebone, change sensors for i2c (although more expensive, better compatibility), and use 3.3v GPIO to flip relays, also get some network cameras instead of cheap webcams I had lying around..
and ps. sparkfun free day was awesome this week. Im all fired up waiting for new parts..
pps. is your parts list distributer mostly sparkfun... cause you could save a lot of money going with digiKey or mouser as a supplier.