Soil Sensor Shows Flip-Dots Aren’t Just For Signs

Soil sensors are handy things, but while sensing moisture is what they do, how they handle that data is what makes them useful. Ensuring usefulness is what led [Maakbaas] to design and create an ESP32-based soil moisture sensor with wireless connectivity, deep sleep, data logging, and the ability to indicate that the host plant needs watering both visually, and with a push notification to a mobile phone.

A small flip-dot indicator makes a nifty one-dot display that requires no power when idle.

The visual notification part is pretty nifty, because [Maakbaas] uses a small flip-dot indicator made by Alfa-Zeta. This electromechanical indicator works by using two small coils to flip a colored disk between red or green. It uses no power when idle, which is a useful feature for a device that spends most of its time in a power-saving deep sleep. When all is well the indicator is green, but when the plant needs water, the indicator flips to red.

The sensor itself wakes itself up once per hour to take a sensor measurement, which it then stores in a local buffer for uploading to a database every 24 measurements. This reduces the number of times the device needs to power up and connect via WiFi, but if the sensor ever determines that the plant requires water, that gets handled immediately.

The sensor looks great, and a 3D-printed enclosure helps keep it clean while giving the device a bit of personality. Interested in rolling your own sensor? The project also has a page on Hackaday.io and we’ve previously covered in-depth details about how these devices work. Whether you are designing your own solution or using existing hardware, just remember to stay away from cheap probes that aren’t worth their weight in potting soil.

Soil Moisture Sensors, How Do They Work?

In a way, the magic of a soil moisture sensor’s functionality boils down to a simple RC circuit. But of course, in practice there is a bit more to it than that. [rbaron] explains exactly how capacitive soil moisture sensors work simply, clearly, and concisely. He also shows, with a short video, exactly how their output changes in response to their environment, and explains how it informed his own sensor design.

At its heart, a moisture sensor measures how quickly (or slowly) a capacitor charges through a resistor, but in these sensors the capacitor is not a literal component, but is formed by two PCB traces that are near one another. Their capacitance — and therefore their charging rate — changes in response to how much water is around them. By measuring this effect on a probe sunk into dirt, the sensor can therefore indirectly measure the amount of water in the soil.

This ties into his own work on b-parasite: an open-source, all-in-one wireless soil moisture sensor (which was also a runner-up in our Earth Day contest) that broadcasts over BLE and even includes temperature readings. One thing to be mindful of if you are making your own PCBs or ordering them from a fab house is that passing current through metal in a moist environment is a recipe for oxidation, so it’s important not to expose bare traces to wet soil. A good coated PCB should avoid this problem, but one alternative we have seen proposed is to use graphite rods in place of metal.

Parts of the automated soil moisture monitoring station

Solar Stevenson Screen For Smart Sprinkler

It’s not infrequent that we see the combination of moisture sensors and water pumps to automate plant maintenance. Each one has a unique take on the idea, though, and solves problems in ways that could be useful for other applications as well. [Emiliano Valencia] approached the project with a few notable technologies worth gleaning, and did a nice writeup of his “Autonomous Solar Powered Irrigation Monitoring Station” (named Steve Waters as less of a mouthful).

Of particular interest was [Emiliano]’s solution for 3D printing a threaded rod; lay it flat and shave off the top and bottom. You didn’t need the whole thread anyway, did you? Despite the relatively limited number of GPIO pins on the ESP8266, the station has three analog sensors via an ADS1115 ADC to I2C, a BME280 for temperature, pressure, and humidity (also on the I2C bus), and two MOSFETs for controlling valves. For power, a solar cell on top of the enclosure charges an 18650 cell. Communication over wireless goes to Thingspeak, where a nice dashboard displays everything you could want. The whole idea of the Stevenson Screen is clever as well, and while this one is 3D printed, it seems any kind of stacking container could be modified to serve the same purpose and achieve any size by stacking more units. We’re skeptical about bugs getting in the electronics, though.

We recently saw an ESP32-based capacitive moisture sensor on a single PCB sending via MQTT, and we’ve seen [Emiliano] produce other high quality content etching PCBs with a vinyl cutter.

Give Your Smart Home A Green Thumb With MQTT

We have all been stuck inside for too long, and maybe that’s why we have recently seen a number of projects attempting to help humans take better care of their housemates from Kingdom Plantae. To survive, plants need nutrients, light, and water. That last one seems tricky to get right; not too dry and not drowning them either, so [rbaron’s] green solder-masked w-parasite wireless soil monitor turns this responsibility over to your existing home automation system.

w-parasite MQTT diagram

Like this low-power soil sensor project and the custom controller for six soil sensors, [rbaron’s] w-parasite uses a “parasitic capacitive” moisture sensor to determine if it’s time to water plants. This means that unlike resistive soil moisture sensors, here the copper traces are protected from corrosion by the solder mask. For those wondering how they work, [rbaron]’s Twitter thread has a great explanation.

The “w” in the name is for WiFi as the built-in ESP-32 module then takes the moisture reading and sends an update wirelessly via MQTT. Depending on the IQ of your smart-home setup, you could log the data, route an alert to a cellphone, light up a smart-bulb, or even switch on an irrigation system.

w-parasite circuit board in a potted plant[rbaron] has shared a string of wireless hacks, controlling the A/C over Slack and a BLE Fitness Tracker that inspired more soldering than jogging. We like how streamlined this solution is, with the sensor, ESP-32 module, and battery all in a compact single board design. Are you asking yourself, “but how is a power-hungry ESP-32 going to last longer than it takes for my geraniums to dry out?” [rbaron] is using deep sleep that only consumes 15uA between very quick 500ms check-ins. The rechargeable LIR2450 Li-Ion coin cell shown here can transmit a reading every half hour for 90 days. If you need something that lasts longer than that, use [rbaron]’s handy spreadsheet to choose larger batteries that last a whole year. Though, let’s hope we don’t have to spend another whole year inside with our plant friends.

We may never know why the weeds in the cracks of city streets do better than our houseplants, but hopefully, we can keep our green roommates alive (slightly longer) with a little digital nudge.

 

A Capacitive Soil Sensor Hack For Lower Voltage Supplies

A frequent beginner project involves measuring soil moisture levels by measuring its resistance with a couple of electrodes. These electrodes are available ready-made as PCBs, but suffer badly from corrosion. Happily there is a solution in the form of capacitive sensor probes, and it is these that [Electrobob] is incorporating in to a home automation system. Unfortunately the commercial capacitive probes are designed to run from a 3.3 V supply and [Bob]’s project is using a pair of AA cells, so a quick hack was needed to enable them to be run from the lower voltage.

The explanation of the probe’s operation is an interesting part of the write-up, unexpectedly it uses a 555 configured as an astable oscillator. This feeds an RC low pass filter of which the capacitor is formed by the soil probe, which in turn feeds a rectifier to create a DC output. This can be measured to gain a reading of the soil moisture level.

The probe is fitted with a 3.3 V LDO regulator, which is simply bypassed. Measurements show its output to be linear, so if the supply voltage is also measured an accurate reading can be gleaned. These probes are still a slightly unknown quantity to many who might find a use for them, so it’s extremely useful to be given this insight into them.

Tired Of Killing Houseplants? Try Using WiFi.

Here at Hackaday, we have to admit to neglecting a few houseplants in our time. Let’s face it… a cold, hard, thinking machine can care for our green friends better than you can. Why not team up? [cabuu]’s WiFi-enabled soil moisture sensor will do the trick in case you, too, want happy plants.

This is one of those projects which would have been much more difficult even five years ago, and really shows how lucky we are to have accessible technology at our fingertips. It’s conveniently constructed from off-the-shelf electronics modules, and nestled inside a 3D-printed case. The design is attractive as well as functional, showing the status LED and allowing access to the USB charging port.

The brain is a WeMos D1 mini, while a D1 battery shield and 14500 Li-ion battery supplies power. A key point of this build is the use of a capacitive moisture sensor, which doesn’t suffer the same long-term corrosion problems that destroy cheaper resistive probes. And no project is complete without an LED, so a WS2812 shows green for good, red for dry and blue for too wet. To extend battery life, the sensor supports a sleep mode, which tests the soil periodically, and presumably disables the LED.

Of course, if you’re a habitual plant-neglector, simply having a moisture probe won’t help; those can be as easy to ignore as the plant itself. That’s where WiFi comes in. [cabuu] wrote a Blynk app to monitor the sensor on a smartphone. The app shows current moisture levels and allows you to change the wet and dry warning thresholds. When the reading exceeds these levels, the app notifies you — this feature is the one that will keep your plants around.

Continue reading “Tired Of Killing Houseplants? Try Using WiFi.”

Raspberry Pi Automates Your Tomato Farm

rpi-tomato-farming

Check out the tomato plants [Devon] grew using a monitoring system he built himself. It’s based around a Raspberry Pi. As far as grow controllers go it falls a bit short of full automation. That’s because the only thing it can actuate is the black water line seen hovering above the plants. But [Devon’s] work on monitoring and collecting sensor data should make it easy to add features in the future.

The moisture sensors pictured above monitor the soil in which the plants are growing. But he also has temperature and light sensors. These are very important when growing from seed and could be used in conjunction with a heating mat for plants that require higher soil temperatures (like pepper plants). The tomatoes are also pretty leggy. Now that he’s monitoring light levels it would be good to augment the setup with a grow light. A long term goal could even be a motorized bed which could raise the plants right up to the bulbs so they don’t reach for the light.

Don’t let the stars in our eyes distract you though. He’s done a ton of work on the project both with the physical build, and in plotting the data collected by the system. Great job!

Continue reading “Raspberry Pi Automates Your Tomato Farm”