Just a little progress update! The garden is going well and a good deal has been grown over this summer. We're really feeling the stress now as the hot weather is here and most of the students have gone home so it's up to a dedicated watering team to keep the plants wet over this period - a problem which the irrigation system will solve! However, another source of sponsorship is taking a while to work with, so in the mean time I have been building an alternative shopping list using the cheapest parts possible. This of course has the added benefit of making it accessible to hackers and makers ;)
One of the most expensive parts of an automatic irrigation system is the valves. These have not had their price driven down like MCUs and wifi modules, so are still pretty pricey. For a typical irrigation solenoid valve the cost is £20 - £40, which is a lot of money considering we need about 21 of them! The lowest cost solution I have found is instead to use cheap washing machine solenoid valves, typically priced at under ten pounds each. However, six of these in each box, which is the current plan, needs quite a large box to space them out with fittings. A neater solution using the same technology is to use washing machine triple valves. These cost about the same as three of the single cheap valves and provide three outlets for each single inlet, saving a huge amount of space! This means I only need two of these in each box.
The valves are available in both mains (240V) and 12VDC varieties, the latter of which will be supplied to each box for the controller, sensors and valves.