Using Backscatter Radio for a Soil Sensor Network

With almost 8 billion souls to feed and a changing climate to deal with, there’s never been a better time to field a meaningful “Internet of Agriculture.” But the expansive fields that make industrial-scale agriculture feasible work against the deployment of sensors and actuators because of a lack of infrastructure to power and connect everything. So a low-power radio network for soil moisture sensors is certainly a welcome development.

We can think of a lot of ways that sensors could be powered in the field. Solar comes to mind, since good exposure to the sun is usually a prerequisite for any cropland. But in practice, solar has issues, the prime one being that the plants need the sun more, and will quickly shade out low-profile soil-based sensors.

That’s why [Spyros Daskalakis] eschewed PV for his capacitive soil moisture sensors in favor of a backscatter technique very similar to that used in both the Great Seal Bug and mundane RFID tags alike. The soil sensor switches half of an etched PCB bowtie antenna in and out of a circuit at a frequency proportional to soil moisture. A carrier signal from a separate transmitter is reflected off the alternately loaded and unloaded antenna, picking up subcarriers with a frequency proportional to soil moisture. [Spyros] explains more about the sensor design and his technique for handling multiple sensors in his paper.

We really like the principles [Spyros] leveraged here, and the simplicity of the system. We can’t help but wonder what sort of synergies there are between this project and the 2015 Hackaday Prize-winning Vinduino project.

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Fully automated watering robot takes a big leap forward toward greenhouse automation


Greenhouse owners might find [David Dorhout]’s latest invention a groundbreaking green revolution! [David]’s Aquarius robot automates the laborious process of precision watering 90,000 square feet of potted plants. Imagine a recliner sized Roomba with a 30 gallon water tank autonomously roaming around your greenhouse performing 24×7 watering chores with absolute perfection. The Aquarius robot can do it all with three easy setups; add lines up and down the aisles on the floor for the robot to follow, set its dial to the size of your pots and maybe add a few soil moisture sensors if you want the perfect amount of water dispensed in each pot. The options include adding soil moisture sensors only between different sized plants letting Aquarius repeat the dispensing level required by the first plant’s moisture sensor for a given series.

After also digging through a pair of forum posts we learned that the bot is controlled by two Parallax propeller chips and has enough autonomous coding to open and close doors, find charging stations, fill its 30 gal water tank when low, and remember exactly where it left off between pit stops. We think dialing in the pot size could easily be eliminated using RFID pot identification tags similar in fashion to the Science Fair Sorting Project. Adjusting for plant and pot size as well as location might easily be automated using a vision system such as the featured Pixy a few weeks back. Finally, here are some featured hardware hacks for soil moisture sensing that could be incorporated into Aquarius to help remotely monitor and attend to just the plants that need attention: [Andy’s] Garden sensors, [Clover’s] Moisture control for a DIY greenhouse, [Ken_S’s] GardenMon(itoring project)

[David Dorhout] has 14 years experience in the agriculture and biotech industry. He has a unique talent applying his mad scientist technology to save the future of mankind as seen with his earlier Prospero robot farmer. You can learn more about Aquarius’s features on Dorhout R&D website or watch the video embedded below.

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Garden sensors measure soil moisture and greenhouse temperature

[Andy] is getting his garden up and running. This year it’s been pretty cold so he decided to get small plastic domed tunnel which acts as a mini greenhouse. To help monitor that environment he built this sensor array which displays temperature and soil moisture readings.

Temperature is quite simple. He’s using a TMP36 sensor which is held a few inches above the soil. The moisture sensor is of his own design. It uses two building screws embedded in foam. These are pushed into the soil and a resistance reading indicates moisture level. By driving voltage on one screw, and measuring voltage on the other he gets some useful data. It’s not a standardized value, but observation over time will let him know how the scale relates to dry or wet soil.

During the build process he found that he needed a pull-down resistor on the probe used to take the moisture measurement. He also uses an I/O pin to drive the other screw. This gives him a way to shut off the juice when not taking a reading. We just hope he’s either got a current limiting resistor, or is using a transistor to drive it high.

Flood triggered camera

When the Department of Natural Resources of Australia decided that they needed to capture data about the natural flooding of a cave, they turned to a hacker to get results. The goal was to photograph the area during these floods with an automated system. In the end, they used a gutted Lumix digital camera mounted in a trash can, covered in aluminium foil. Though it sounds a bit silly, the final product turned out quite nice. You can see the build log, schematics, and results on the project page.

[via hackedgadgets]

Soil moisture sensing

These plugs are cheap, easy to make, and work well for measuring the moisture content of soil. The Cheap Vegetable Gardener came up with this method in order to add automatic watering to an automated grow system. Plastic tubing is used as a mold for Plaster of Paris. Once the plaster has been poured, two galvanized nails are inserted. These are won’t rust and work as probes, measuring the resistance of the dried plaster (gypsum). When inserted into the soil, the moisture content within the gypsum will fluctuate along with the soil. As moisture rises, the resistance between the probes falls, which can be monitored by a microcontroller and used to trigger or stop a watering system.

[Thanks Juan]