Hydroponics - the technique of cultivating plants in water containing dissolved nutrients in a controlled environment without soil.

Hydroponics is not something new, 600 BC, the hanging gardens of Babylon are the first signs of horticulture using water. The reason I became interested in hydroponics started when I was in the Caribbean, I noticed the island of Aruba has a hot dry tropical dessert climate with a constant western wind blowing, few natural resources, and everything has to be imported from external countries.

Agriculture on Aruba is very limit due to climate and scarcity of natural water. However what it does have going for it is a tropical temperature, permanent wind and year long nearly constant daylight hours. I thought this could be a good starting point on the grounds that the missing components, mainly water can be overcome. Temperature will be an important factor that needs very careful consideration.

It became very clear that hydroponics, due to the fact that it can save more than 90% of water usage in comparison to open field agriculture in this dessert tropical climate was the way to go.

Cultivation

Propogating tomato suckers

Cultivation and propagation can take place in two ways. Sprouting seeds, or using cuttings.
Using cuttings from an existing plant is faster and ensures the genetic material of the new plant is the same as the parent.

Fruit/Vegetables

Hydroponic tomatoes

Hydroponic plants in a controlled environment generally grow faster and produce more plant material than the same plants in open soil. They produce more fruit and are less prone to disease and infections from insects and the likes.

Compact/Vertical

Indoor hydroponics

More and better quality produce can be obtained from a much smaller area as opposed to growing the same plants in ope ground. By ensuring ideal conditions like light, temperature, humidity and water nutrients.

Managed and Controlled

Hydroponics controller prototype

Using a network connected MCU (ESP32) not only can we measure, monitor and register environmental parameters like temperature, humidity, light, water level, EC and PH and send this as telemetry to a database for analysis, but we can also control these parameters.

Can it actually work? was my first question. Thus to prove I have the capability an environment to test it was set up. To mimic tropical day/night cycles, 200Watt full spectrum LED light modules were obtained. For test purposes, heaters and Peltier elements are used to heat the environment and nutrient solution to mimic tropical conditions. Obviously once in such environment, the opposite will be applicable, thus cooling the environment and water.
Being a wildlife enthusiast it should not surprise you that there are several reptiles that share what I call home. The love warmth and as such the tropical hydroponics proof of concept was setup in the same room. It is a win/win situation for flora and fauna.

Challenges

  • Low water consumption
  • Low energy consumption
  • Optimal use of space
  • Large produce volume
  • Constant produce
  • Gather data
  • Learn from data
  • Gain experience

What form of hydroponics to use: I considered NFT (nutrient film technology), but this involves 24/7 pumps running and any cooling of the nutrient solution will soon be lost as it flows through the piping system to feed the plants. The initial setup was using empty buckets from a local snack bar. Here sweat peppers (capsicums) were placed in a flower pot with loads of small holes for the roots and then hydroton (expanded clay pellets) were used to hold the actual plant. Bucket nearly filled with nutrient solution and added an airstone powered by a small solar panel.

Babylon did intrigue me, so a small vertical wall with 18 pods for leafy green like salad was also added to hydroponics setup. Here a small pump (aquarium 12V) is used to pump the nutrient solution from a container at the base to the top of the wall where it flows down towards the reservoir at the base of the wall. On its way down it flow through cupped containers and replenishes the water for each container.

Vertical hydroponics

Vertical hydroponics wall

Different hydroponics setup

Two types of hydroponics systems are tested. One the 'Kratky" method, in basics, a bucket of nutrient rich water with the plants roots submerged in the fluid. And secondly a vertical "Ducht bucket" system. This comprises of multiple rows of containers stacked on top of each other. Water from a higher elevation reservoir is allowed to flow into the top row of containers and as these fill up, they overflow into the containers below. At the base is a receiving reservoir that collects the water. When full uses a 12V solar powered water pump to refill the top container.

Hydroponics and Technology

Many points of concern are on the table when engineering for low power (read ECO friendly) semi-self operational hydroponics systems. This not even taking the mechanical end environmental engineering into full account. The concept is to have one or more low power functional units that monitors and manages the different aspects needed for an optimal hydroponics environment for the plants that are grown in it.

  • Air temperature
  • Air humidity
  • Water level
  • Water temperature
  • Water PH (Hydrogen potential)
  • Water ORP (Oxygen reduction potential)
  • Water TDS/EC (Total Dissolved Solids)
  • Light LUNS (Sun/LED Light)

Hydroponics KPI's

Key points of interest is the environment that the plants are in. The purpose of automation and AI is to monitor the environment using sensors, register this information and observe plant behavior with as goal to determine the most optimal growing environment for the plants.

Researching sensors for the key points of interest, choices were made to make a proof of concept. Main concerns were precision and durability in relation to cost. This left a lot to be desired. Most affordable sensors were not suitable for continuous use. The TDS/EC sensor probe in continuous operation in fluid reacted with the salts that were in the water due to a constant current (even though AC and not DC) running through it. The cheap PH sensor probe has the problem of the 'control' media being in 'semi' contact with the fluid being tested, eventually natural forces of osmosis cause the control fluid to become so diluted, measurements are no longer anywhere near what they should be. There is a solution, ISFETs, but not in scope at present due to the high cost.

Sensor choice was based on absolute need and cost. This did result in certain sensors being changed during development as they were just not accurate at all.

Sensors for hydroponics POC

Hydroponic sensors

Hydroponics and Telemetry

Measuring important parameters like time of day, temperature, light intensity, nutritional water parameters and plant growth parameters are vital to determine and maintain ideal conditions for plant growth. The requirement is to automate sampling these parameters at given rates and registering the results in a database for smart analysis and eventual automated control. This can and should be done in parallel systems, at least two, and is used to experiment on what differing certain set and controlled parameter(s) have on plant growth.

Low cost, low energy, low maintenance, fault tolerance (possible fail over) are the main criteria when looking at possible automation systems and platforms. At present the Espressif Systems ESP32 range of products is capable of very low power operations when needed and is powerful enough for AIoT implementations when wanted with integrated WiFi and BlueThooth BLE implementation at an amazing low price. This is my GoTo as it intrinsically runs on RTOS (Real Time Operating System) allowing for smart energy efficient routines running simultaneously.

Data collection, analysis and acting on results is crucial in to an efficient way to find the best possible growing conditions for a specific type of plant.

Controller Design and Construction

Multiple domains (like water level and temperature, PH, nutrient levels and more) need to be monitored and controlled. This means sensor inputs and also control outputs, usually power control for lights, pumps and motors or actuators. Here N-type MOSFETs (metal oxide field effect transistor) were chosen. The reason is two fold, unlike normal transistors that use current to 'switch', generating heat and power loss, FETs use potential difference and not current to operate = low power = no power loss. The second reason FETs were chosen is their ability to switch on and off real fast, this allows us to use PWM (pulse width modulation) to drive the outputs. With PWM we can control motor speeds for water pumps and nutrient dosing pumps and also control the LED light intensity levels.

Some sensors produce digital output which is ideal for direct processing by the computer unit, however not all sensors are digital, and example is the LDR (light dependent resistor) to measure the light value. These sensor outputs need to be converted to a digital signal or value, this calls for an ADC (analog to digital converter) unit to make it possible to read these types of sensors.
Finally a small display unit is attached to be able to visually see the status of the system and what it is busy with at any period of time.

Schematic Diagram

Hydroponic schematic design

Controller Construction

Hydroponic PCB Layout

PCB considerations

Determining what sensors, actuators, connectors and other operational components are required is one thing. Putting them all together in such a way that they can all operate together in an effective and efficient way is another domain. This is where PCB (printer circuit board) design becomes important. There are a multitude of things that need to be taken into consideration. An example is working with signal 'wires', these do not carry heavy current and can thus be thin, however switching LED light of 150 Watts needs a thicker 'wire' to be able to handle the 'high' current is needs to work. Thus power rails for the FET switches need appropriate thickness PCB tracks to be able to handle the current they may be called on the switch when in operation.

The placement of the components should be such that they are practical for the purpose they serve, like connectors for attaching controllers like lights or motors etc. Thus the power connectors are at the edge of the PCB and chosen to be suitable for the power rating the circuit was designed for.

Spacing between power items like the FETs must be taken into consideration, as where power is used, heat can be generated. To ensure the components can vent possible heat buildup and have to ability to attach heat sinks if required, all power components have additional 'safe' space around them to prevent heat affection other components in the vicinity.

Hydroponics controller PCB

Hydroponic Controller PCB

A view of the power rail components. Consideration has been made that any or all MOSFET switches could be used to switch motors and/or control their speed and can/will generate back EMF which is not wanted as it can damage the MOSFETs. Diodes in reverse conducting mode are placed across the source and drain of the MOSFET to protect it from any voltage spike caused by switching inductive loads like motors or relays etc. Each MOSFET switch has a LED to indicate its status, making it easy to see which is switched on or not.

Main Components

Components

Hydroponics Dashboard

Operational Hydroponic Dashboard

Information to follow...

ESP32 Web Server and Sockets

Hydroponic Dashboard

Firmware and software design and development...