OpenSprinkler › Forums › Hardware Questions › OpenSprinkler Pi (OSPi) › 3 wire ball valves and multi moisture sensors on the OSPi board › Reply To: 3 wire ball valves and multi moisture sensors on the OSPi board
It’s tricky, if not impossible, to modify OSPi to interface with 3-wire motorized ball valves. The first reason is that OSPi runs on AC power, while this valve requires DC power. OpenSprinkler 3.0 DC-powered would be able to interface with this valve, but even so, a hardware modification is needed: OpenSprinkler uses common anode (positive) design, while this valve requires common cathode (negative). Basically, the valve needs the common wire to be ground, while the controller has common wire dedicated to positive. As a result, you will need a transistor adapter to invert the logic of each zone. I’ve actually designed this transistor adapter (basically made of a PNP transistor on each zone) for another customer, and I’ve tested it to work well with 3-wire ball valve. The way it works is that each motorized ball valve will take over 2 zones, one for opening, one for closing. Let’s say the valve take 10 seconds to open (or close), so you have a program that does 10 seconds on the ‘open’ zone, that will open the valve at the designated time. Similarly for the ‘close’ zone.
So in short, it’s difficult to modify OSPi to interface with this valve. OS 3.0 DC-powered can, and it requires an adapter to do logic inversion, and I do have that adapter as well.
Do not that among the different types of motorized ball valves, there is a ‘2-wire auto return’ type, which would be the easiest to work with OSPi or OS, as it would not require either hardware or software modification.