This project is part of a full home automation solution implemented on our residence. The design shown here has 8 stations with no humidity feedback, which is quite sufficient for most residential projects. It can be expanded to up to 64 stations for commercial installations.
If no humidity feedback is required, the cheapest solution is to use the 8-Relay Expansion Card (available soon) This stackable card for the 40-pin Raspberry Pi family packs 8 relays in the same form factor with Raspberry Pi.
Humidity sensors are cheap and can provide a water saving solution in regions where there is a shortage of water, like California. The Mega-IO card (available now) has 8 analog inputs, which could read the humidity from 8 irrigation zones.
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