THE THEORY OF CREATING AUTOMATIC AEROPONICS SYSTEM FOR GROWING PLANTS

ABSTRACT

In this article we attempt to explain how to build a fully automatic aeroponic [1] system. We will discuss what embedded systems we can use and. We will also consider some principles of connecting sensors to the system for controlling the quality of the plant nutrient solution. Also described are the main sensors for complete control inside the greenhouse and some essential safety systems. Many of the problems associated with such systems can easily be solved with good coding applications and the right sensors. The purpose of this article is the creation of a fully controlled aeroponic system and to define the main ways in which software algorithms are used to manage the complete system.

АННОТАЦИЯ

Эта статья описывает, как построить полностью автоматическую аэропонную систему [1].  Какие встроенные системы мы можем использовать. Мы также рассмотрим некоторые принципы подключения датчиков к системе для контроля качества удобрений. Также будут описаны основные датчики для полного контроля теплицы и некоторые важные системы безопасности. Целью данной статьи является создание полностью контролируемой аэропонной системы.

Keywords: hydroponic, aeroponic, embedded system, sensors.

Ключевые слова: гидропоника, аэропоника, встраиваемые системы, сенсоры.

Introduction

There are two principles to grow plants.  By using soil, in the traditional manner, or by using a hydroponics system. Hydroponic systems are technological and require a certain amount of knowledge not only about growing plants, but also about maintaining the system itself. In hydroponic systems, no soil is used. Hydroponic [2] systems can also be subdivided into separate subsystems known as substrate and non-substrate systems. In hydroponic systems, use mineral wool or coconut coir. The main point to note is it should be a porous storage material that is well ventilated, allows moisture to pass through, is totally inert to chemical processes and does not change the PH balance or change the chemical composition of the fertilizers that are added to this substrate. Such systems are similar to conventional planting in soil. The second type of hydroponic systems however are systems where there is no substrate. The plant is completely or partially dipped into a plant nutrient solution.

In this article we are going to discuss an aeroponic system. We will talk about the sensors and equipment necessary to build a fully automatic aeroponic system. An aeroponic system is one where the plants are grown in tanks and the plant nutrient solution is sprayed under great pressure onto the roots.  This forms a fine mist after which the nutrient rich solution is pumped back into a common tank in a cyclical process again and again.  The main difference between a hydroponic system and an aeropinic system is that the roots of the plant are not all the time immersed in the plant nutrient solution, but only at certain times when they pressure sprayed. This is especially true in a growing tent and not in open ground because it is easier to control everything in a growing tent than outside.

Description of the concept

In this article I would like to tell you about the technical and software solutions for building a fully automatic aeroponic system for growing plants [1]. But first, I want to emphasize here that the main point of aeroponics is to spray an ultra-fine mist that will settle on the roots of every plant.  Aeroponics is about creating a fine mist. It is not just spraying and irrigating plants as is the case when, for example, watering a lawn. I will not in this article discuss which method of growing is better, and which is worse, I will just stick to the main technical details. The system I wish to discuss consists of two large tanks of 50 liters each, four tanks of 20 liters each with a reverse osmosis filter without mineralization, full spectrum LED lamps, a filter with an extractor and a fan to draw in air. I can manage and control the whole system by using the Arduino developing board. This is more than adequate to control my type of system. Most sensors can be found and purchased from robotics websites. Usually, the most popular sensors have ready-made code libraries which can easily be modified for your own purposes. You can also obtain the tubes and adapters needed for the pneumatic systems process. They hold pressure very well and can be easily modified.

The plant nutrient solution

This is the most complicated part of the project and it consists of two stages.  The first stage is to inject the plant nutrient solution into small tanks.  This is done at regular intervals from a large tank and when the plant nutrient solution reaches a certain level in these tanks, usually not more than 10% of the total tank volume, the plant nutrient solution must be pumped back into the larger tank. For injecting the plant nutrient solution into small containers, you need to use a High Pressure Diaphragm Pump. A (160 PSI) will be sufficient for 12 spraying nozzles; that is two nozzles per container. A single compressor can serve 6 small containers. To control the injection, you will need an adjustable programmable code that will allow you to turn the injection on and off at different intervals. The injection time depends on the specific growth period of the plant and certain other factors such as time of day, lighting conditions etc. It is very important to add a keypad to the control system to be able to control all changes during the plant growth phase. The second stage is to pump the plant nutrient solution from the small containers into a common big tank.

Liquid level sensors are mounted in the control small tank where our plants are grown. Liquid level sensors control the maximum and minimum filling of the tank, in our case it is no more than 10% of the total volume of the tank. We can leave the ends of the roots in the plant nutrient solution in case something fails in our system – and this will give us time to fix the problem. When the liquid gets close to the top level sensor, a second compressor is turned on and all the liquid is pumped back into the large tank. The compressor will turn itself off when the liquid gets close to the lower level sensor reading. To pump out the liquid from the small tanks and also to change the plant nutrient solution in the big tank we use another type of compressor. This is a water booster pump. If this compressor develops an air lock during operation it will continue to function, which is very important for the smooth operation of our system. Approximately once a week we need to drain all the plant nutrient solution from the big common tank, pour in fresh filtered water from the second big tank and make a new plant nutrient solution. The pipes we use in our system have solenoid valves which are electronic faucets that can be opened and closed using our software. Using the same pipes we are able to drain our entire tank of the used fertilizer mix and switch to pouring in clean filtered water into the tank and to begin the preparing a new plant nutrient solution. About every few days we should drain all the old mixture from the common tank and pour in fresh filtered water from the ‘filtered water’ tank. There are scales under the common tank that are connected to our controller. In this way we can monitor how much filtered water we need, and also the daily liquid consumption of our plants. The data on how much liquid the plants are using allows us to adjust the fertilizer in our plant nutrient solution.  Perhaps the most challenging part to implement is the coding and technical requirements for the unit that controls and mixes the nutrient solution in the tank. For the sensors controlling the humidity or the temperature we can use a ready-made code from the manufacturer.  With the PH and EC sensors we have to write the code ourselves. We also have to make the dispenser mechanism. 

The PH sensor, EC sensor and temperature sensor controls are used in the tank mixture.  A PH sensor is needed to control the acidity of the plant nutrient solution. An EC sensor shows us the amount of the plant nutrient solution added or consumed by the plants. This allows us to monitor in real time all the plant nutrient solution in the system. In this project, I am using GHE fertilizers, which is a set of three separate ingredients bought in bottles. I also use two bottles for PHUP and PHDOWN and one bottle for CalMag. Because our water is derived from a reverse osmosis filter, the water does not contain any naturally dissolved minerals.   In this case we need to add calcium and magnesium using six peristaltic pumps with very fine gauges to control accurately the dosage of added substances to the main tank. We need to adjust and control the PH and EC levels daily, not just during the creation of new nutrient solution. The code required for doing this is quite complicated and requires some experience in and knowledge of growing plans. Common sensors for controlling the whole greenhouse are best done using the I2C [3] protocol. We use a lot of different sensors and in that case, our embedded system will not have enough pins for connection. Also, by using I2C [3] protocol we can build our system logically and correctly.

Sensors for general control of the greenhouse

Let us begin with the humidity sensor. The level of humidity inside a greenhouse is a very important indicator of the health and promulgation of plants. If you do not control the humidity, there will be problems with mold and mildew and you may have to destroy the crop or, the moldy atmosphere will significantly impair the final flavor. In an aeroponics system all the liquid is in a closed system and evaporation of water from the surface of leaves only. Of course, it goes without saying, a situation where there is not enough humidity is also bad. Thus, we have to monitor the humidity at all times and especially in the different growth stages of the plants.  I am using an SHT40 sensor. It is a very accurate sensor that is perfect for the greenhouse and can accurately measure temperature. This sensor controls two further devices connected to an Arduino: a humidifier and a dehumidifier. When we have too much humidity we switch on the dehumidifier, and when we have too little we switch on the humidifier.

The temperature sensor shows us the temperature and it is also connected to the Arduino which also controls a supplementary back-up fan. We always have at least two fans running simultaneously as well as the extra back-up in case the temperature rises too high. Mounting a cooling system is not always applicable because of installation difficulties and high electricity prices.

Some growers also use inside their greenhouses various homemade CO2 dispensers or buy in additional gas bottles. In all cases, CO2 needs to be carefully monitored and controlled. CO2 in high doses and especially in a closed space like a greenhouse, can be toxic to humans. I use the sense air s8 for CO2 control. It is a reliable and accurate sensor that is easy to install and comes with a ready made code supplied by the manufacturer. The sensor efficiently controls the extra extraction fan to ensure the correct amount of CO2 in the greenhouse. When the CO2 level is above the required level the Arduino turns on the relay and equalizes the CO2 level. 

Since this is an aeroponic system (also applies to any hydroponic system), we have to keep track of any leaks inside the greenhouse because the liquid in the tanks is pressurized and there is a small risk of a pipe bursting. I have put a mh-rd raindrop sensor on the floor of the greenhouse. As soon as the liquid falls onto it I get an instant message from the sensor and this enables me to fix the leak.

We know that the plants smell very strongly especially during the flowering stage. We have therefore put charcoal filters inside the greenhouse to neutralize the smell. However, the filters occasionally stop working for one reason or another. As a result, I recommend installing the CCS811 sensor on the exterior of the greenhouse. This is a volatile organics odor sensor. We have to set the odor level to normal.  If for some reason the odor level goes up, that is a signal to us that something has happened to our filters in the greenhouse.

Not all of the sensors in the greenhouse are wired to the Arduino and some are connected wirelessly. For this purpose I use 433MHZ Wireless Transmitter Receiver modules.  The batteries that power the transmitter and the sensor are very good and can last for several years of continuous operation.

To Arduino, we can connect display with buttons for correcting and adjusting all the sensors. Also, the Arduino board has a Wi-Fi module. This has made it possible to insert a software server and to transmit and receive data over the internet. On the basis of any free service where you can open your site, you can build a database from any sensor which you use in the greenhouse and visualize it.  You can also if necessary retrieve the data in real time and customize it to your needs. By taking advantage of the NodeJS [4] framework we can get the data in real time and implement it in easy to read graphs.

Conclusion

As we can see in this article, to create a fully automated greenhouse requires a lot of experience not only in electronics and programming, but also you will need to understand what plants need at every stage of the growth cycle. However, the good news is that components, sensors and solutions are available from many companies, and you can find relatively easily everything you need to automate your greenhouse.

References:

1. Paolo Sambo, Carlo Nicoletto, Andrea Giro, Youry Pii, Fabio Valentinuzzi, Tanja Mimmo, Paolo Lugli, Guido Orzes, Fabrizio Mazzetto, Stefania Astolfi, Roberto Terzano, Stefano Cesco, Hydroponic Solutions for Soilless Production Systems: Issues and Opportunities in a Smart Agriculture Perspective, Front. Plant Sci., 24 July 2019 Sec. Plant Nutrition, pp 3-8.
2. Bethany M. Eldridge, Lillian R. Manzoni, Calum A. Graham, Billy Rodgers, Jack R. Farmer,Antony N. Dodd, Getting to the roots of aeroponic indoor farming, New Phytologist, Volume2 28, Issue 4, Pages1 183-1192.
3. Randall Hyde, The Book of I²C: A Guide for Adventurers, Publisher No Starch Press, ISBN-10 171850246X, pp 10-32.
4. Jim R. Wilson, Node.js the Right Way, Publisher The Pragmatic Programmers, ISBN10 1937785734, pp 15-65.
5. Peter Marwedel, Embedded System Design: Embedded Systems Foundations of Cyber-Physical Systems 2nd ed. 2011 Edition, Springer Verlag, pp 55-90.
6. Dogan Ibrahim, Designing Embedded Systems with 32-Bit PIC Microcontrollers and MikroC 1st Edition - August 22, 2013, Newnes, DOI https://doi.org/10.1016/C2011-0-06919-3, pp 106-122.