The firmware is completely open source Arduino code, and is hosted on github. The kit doesn’t come with a 24V transformer, so I salvaged one from one of my DewBees. You can see in the photo below that the rightmost 4 triacs are all askew due to my messy rework: I inadvertently soldered 4 of the triacs on the main controller board backwards, and had to clip the leads and solder them onto the top of the PCB in order to reverse the connections. It took me about 3.5 hours to assemble both the main board and extension board, and one hour of that was spent undoing a careless error on my part. The step-by-step assembly instructions are very clearly written, with lots of photos, and easy enough for even a noob to follow. Ray’s Hobby has great documentation on their website. The components were also bagged in separate groups, which made finding the parts easier: The kit came nicely packaged, with bubble wrap protecting all of the delicate parts: Shipping was very fast, and I received a box a few days after I placed the order. Pre-assembled SMT boards are also available at higher cost.
Since I needed 14 channels, I ordered a DIY OpenSprinkler 1.4u kit ($89.99) and an extension board ($25.99).
In the front yard alone, there are 14 channels, which have been controlled by two very old Irri-Trol DewBee 7-channel units. My house has a crazy amount of sprinklers.