Hydroponics - Farm That Drinks Sunlight and Texts Us Its Feelings

Many hydroponic systems require a constant source of water and most require manually checking the status of the system. We set out to make a mobile smart farming cart capable of growing spinach without soil, distilling water using only sunlight, and monitoring itself.

Using the Nutrient Film Technique, spinach grows in a stream of nutrient rich water while a solar powered still produces distilled water from salt water. An ESP32 takes readings of pH, TDS, water temperature, air temperature, and humidity and relays them to a user via an application on their phone.

Using readily available materials such as PVC piping, glass, sensors and some trial and error the project came to a cost of about 240$. Let's get into the rest of the Instructable and get you started on your own smart farming cart!

Here's everything you put in the shopping cart:

Frame

1. 1.5" UPVC pipe (the main pieces) + 1" UPVC pipe (the crossbar pieces)
2. 2" UPVC pipe x3, 1 m long, drilled with 6 holes in each piece — this is where the spinach will grow (18 plant spaces in total)
3. UPVC tees, elbows, couplings and bushes to connect everything like Lego pipes
4. Tubing for the "dirty water returns to the source" line
5. A plywood base + 4 castor wheels (to make your farm mobile like a green shopping cart)
6. 8 mm float glass + 6 mm tempered glass (for the solar still)

Flow System

1. 40W submersible pump x2
2. Two 20-liter buckets — one with fresh water, another with the dirty water entering the still
3. NFT net cups (root holders for the plants in the channels

Electronics System

1. ESP32 dev board
2. DHT11 sensors x2 (one for the canopy of the plants, the other around the solar still)
3. DS18B20 waterproof temperature sensors x2
4. Analog pH sensor
5. Analog TDS sensor
6. Water level sensor
7. Relay board x4 channel
8. 12V 5A SMPS power supply and buck converter
9. Full spectrum LED grow lights
10. Jumpers, wires, and connectors galore, plus heat shrink tubing so nothing sparks

Software Components

1. Arduino IDE
2. Blynk App

Plant Requirements

Hydroponic nutrients, spinach seeds, and seed germination trays

Miscellaneous

M-seal, teflon tape, silicone, zip ties, and paint – those overlooked components in every DIY project

The project is an amalgamation of three technologies that make up one mobile system. Unlike other individual technologies that may provide only one of the required solutions, the hydroponic farming cart produces spinach, desalinate water by using solar panels, and monitors the conditions of the plants.

While the cart may seem like a complicated system, it is a complete self-contained and self-monitoring food producing system. Anyone can replicate, modify, and create their own hydroponic farming cart with a little bit of material and the willingness to experiment.

We know, everyone hates sitting in the CAD program when they could be cutting pipe. But please, do this step once is better than twice.

1. Is the water actually flowing downhill?

The NFT pipes have to be slightly angled so that gravity does the job rather than you having to stand there all day long and tip the pipes yourself.

1. Will the solar still actually drip where you want it to?

We've got the sides of our solar still tilted at 25°, by cutting one at 25 inches height and another one at 11.3 inches height, so water will roll down into the collecting funnel and won't simply fall back into the dirty water below.

In short: draw it out, do some math, then pick up your saw.

1. Cut your 1.5" pipes into four vertical supports of the frame.

2. Cut 1" pipes to act as crossbars and mount points for the grow lights.

3. Assemble the frame without gluing anything first so that any mistake in measurements could be fixed without problems.

4. Screw the assembled frame onto the plywood base with castor wheels. Yay! Your farm just got wheels — and you know what that means: it's the coolest upgrade ever.

5. Place rigid pipe from the fresh water tank up to the grow channels’ top level, since this will be the supply line of the pump. Flex pipe must be used for the return line to allow gravity to drain the excess water.

1. Cut three pieces of 1m long UPVC pipe, each 2 inches wide.

2. Drill 6 holes into each piece evenly so as to provide 18 spots for net cups.

3. Attach the channels to a slight down-ward sloping position.

4. Fix your full spectrum LED grow lights on the crossbars just above the channels, so as to give enough lighting but to prevent burning the spinach.

The pump provides continuous flow of oxygenated nutrient water over the roots of the plants and allows gravity to recycle the excess water back into the reservoir.

This really feels magical when it is done successfully for the first time.

1. Create a basin made out of 8 mm float glass (22 cm x 45 cm) with a sealant that will make it water-tight.

2. Design the sides of the basin in such a way that you will have a 25° angle.

3. The cover will be made of 6 mm toughened glass at an identical angle.

4. Attach a small funnel to the lowest point where the condensed water will accumulate and will drain to your fresh water reservoir.

How the magic happens: dirty/salt water is poured into the basin, the sun will heat it up and will make it evaporate; then it will come into contact with the cold glass cover and will condense back into pure water droplets that roll down along the slope into the reservoir.

Fun fact check: The evaporating area is just 0.099 m² (the size of a big pizza box), so you shouldn’t be expecting gallons, but it is enough to replace what the plants lose via transpiration. This would be the part that you should consider scaling up if you were ever planning to build a larger version of this setup.

1. ESP32 is the brain of the whole system powered by 12V, reduced to 5V.
2. DHT11 x2 → for measuring the air temperature/relative humidity, with one probe close to the plants and another next to the solar still.
3. DS18B20 x2→ temperature probes underwater, one in the reservoir and another in the solar still.
4. Analog pH sensor→ placed in the reservoir and monitoring the acidity/basicity of the water.
5. Analog TDS sensor → another sensor in the reservoir for measuring the nutrient density of the water.
6. 4-channel relay→ used as an electromotor controlling the pumps and the lights, because the ESP32 itself cannot control any high-voltage circuits directly.

Make sure your electronics are safely tucked inside a waterproof box and use heat-shrink tubing for all of your exposed soldered joints to prevent your project from being electrocuted spinach.

1. Program the firmware using Arduino IDE. What does the code do, exactly? Well, nothing more than loop infinitely by doing the following steps:

1. Read data from all sensors
2. Filter the noisy readings of pH and TDS sensors
3. Transmit data through Wi-Fi to Blynk
4. Turn relays ON/OFF for lighting and water pumps as needed

2. Create the Blynk dashboard displaying temperature of water, temperature and humidity in plants, temperature and humidity of solar still, TDS and pH measurements, and ON/OFF controllers for lighting and water pumps.

3. Place the pH and TDS sensors in calibration buffers before your first attempt to use the device.

We chose spinach (Spinacia oleracea) for our first crop since it is easy to grow and is not picky about anything.

Nursery stage (Days 1-15),

In the germination tray:

Data is given above in the table

Main channel stage (after Day 16):

1. Put your seedlings (in their starter plugs) into the net cups.
2. Increase the TDS concentration to 800-1000 ppm, spinach becomes more greedy as it grows.
3. Maintain pH at the level of 5.5-6.0 to allow proper absorption of iron and nitrogen by the crop.
4. Keep the temperature at a comfortable level of 18-20 °C. Warm water contains less oxygen and the unhappy roots lead to root rot.

Set up the photoperiod to be 14 hours per day, just as your dedicated grow light timer.

Absolutely! This is what we achieved with the setup is given above. The frame did not sway under the weight of water and glass, the Blynk dashboard updates happened without any lagging, and the solar still provided an endless supply of perfectly pure water for the plants. 10/10, will grow again.

Integrate tiny nutrient pumps that will allow the ESP32 to correct the pH and the concentration of nutrients by itself

1. Essentially provide the system with hands, not only eyes.
2. Put in some phase change material in the solar still that will keep the water production going into the evening instead of shutting down at the end of the day.
3. Improve the solar still if you wish to make the entire grow rack work on self-produced water.