Vineyard + Arduino = Vinduino
Given the current water crisis affecting the Golden State, farmers are constantly seeking alternative ways to reduce agricultural consumption. Take Reinier van der Lee, for example, who has developed a solution that can cut H2O use by up to 25%. And for that reason alone, it makes for an excellent Hackaday Prize entry.
The project, which is aptly named Vinduino, began as a necessity to better manage irrigation on his Southern California vineyard. However, it’s not just the U.S. west coast that is impacted by drought. There are 36 countries, spanning from Africa to India, that are facing similar situations due to lack of rainfall. With this in mind, van der Lee hopes that his DIY system can reach a widespread audience by making it open source, affordable, and easy to build.
As a whole, the system is comprised of calibrated gypsum soil moisture sensors, a handheld sensor reader and a solar-powered remote platform. Based on an Arduino Pro Mini (ATmega328), the Vinduino is equipped with three inputs for soil moisture sensors, an RTC module, a load switch, irrigation valve control, and wireless communication via either a ESP8266 Wi-Fi or a long-range RF module. Most recently, the Maker installed extra gypsum sensors and implemented a 4G hotspot for Internet access on his vineyard by connecting to the ESP8266.
“Using a single soil moisture sensor, you can determine when to start irrigation, but overwatering is hard to avoid,” van der Lee writes. “By the time the irrigation water reaches the sensor, the layer above is saturated and likely there is more water than the plant can consume. The surplus water will now seep below the root zone, out of reach of the plant, taking unused nutrients with it as well.”
Instead, this problem was solved by using three sensors. The lowest most sensor is placed below the roots, so it should never go off. If it does, this means that the plant is not taking in all the water, and subsequently, the output can be reduced. The two sensors above it monitor the H2O as it transitions through the soil, and adjust the water amount and interval frequency accordingly.
With multiple sensors located at various depths, users can actually control irrigation to not exceed the active root zone, thereby saving water. Rather than have to irrigate for an extended amount time and with long periods of rest in between, Vinduino allows for much shorter, more frequent irrigation cycles. The result? The plants will be able to absorb the water before it even has a chance to reach the level below the active root zone. It is important to keep in mind, though, that different crops call for different depths. For instance, recommended sensor depths for grape vines are 24, 48 and 60 inches.
Resistive sensors, like gypsum sensors, need to be excited with short pulses of alternating current to avoid electrolysis effects. The Vinduino interface alternates currents through the sensor, while a pair of analog inputs are utilized to measure voltages over the bridge. This compensates for differences in battery supply voltage, as well as sensor bias voltage.
Since the sensors are connected together through a soil resistance path, multi-sensor measurements can only be achieved if the sensors are disconnected when not in use. For this, Vinduino employs regular 2N7000 FETs. The handheld reader is capable of only measuring one sensor at a time, thus can use a simpler interface circuit without FET switches.
For vineyards, irrigation reduction is sometimes practiced in the days leading up to harvest in order to get highly-concentrated wine grapes. The idea is that the best wines come from vines that have suffered water stress. In case you’re interested in van der Lee’s status, his vines are doing well under the new irrigation regime.