Step 2: Arduino + Ethernet shield
3 digital pins are controlling 3 relays that let the 24v AC through.
A 4th digital pin is used for the ground for convenience sake, really (the connector that came with the relay board conveniently had 3 relays + ground on 4 adjacent pins... if that makes sense...).
An old cell phone charger gives me 10v DC which I get to the arduino through the Vin + GND pins.
Finally, I added a couple of push buttons for manual control. I use the Analog input trick (different resistor values give different analog reads for each button). In the end I only used one of them.