We live in a world where everything can be controlled and operated automatically, but there are still a few important sectors in our country where automation has not been adopted or not been put to a full-fledged use, perhaps because of several reasons one such reason is cost. One such field is that of agriculture. Agriculture has been one of the primary occupations of man since early civilizations and even today manual interventions in farming are inevitable. Greenhouses form an important part of the agriculture and horticulture sectors in our country as they can be used to grow plants under controlled climatic conditions for optimum produce. Automating a greenhouse envisages monitoring and controlling of the climatic parameters which directly or indirectly govern the plant growth and hence their produce. Automation is process control of industrial machinery and processes, thereby replacing human operators.
1.1 CURRENT SCENARIO
Greenhouses in India are being deployed in the high-altitude regions where the sub- zero temperature up to -40° C makes any kind of plantation almost impossible and in arid regions where conditions for plant growth are hostile. The existing set-ups primarily are:
1.1.1 MANUAL SET-UP:
This set-up involves visual inspection of the plant growth, manual irrigation of plants, turning ON and OFF the temperature controllers, manual spraying of the fertilizers and pesticides. It is time consuming, vulnerable to human error and hence less accurate and unreliable.
1.1.2 PARTIALLY AUTOMATED SET-UP:
This set-up is a combination of manual supervision and partial automation and is similar to manual set-up in most respects but it reduces the labor involved in terms of irrigating the set-up.
1.1.3 FULLY- AUTOMATED:
This is a sophisticated set-up which is well equipped to react to most of the climatic changes occurring inside the greenhouse. It works on a feedback system which helps it to
respond to the external stimuli efficiently. Although this set-up overcomes the problems caused due to human errors it is not completely automated and expensive.
1.2 PROPOSED MODEL FOR AUTOMATION OF GREENHOUSE
The proposed system is an embedded system which will closely monitor and control the microclimatic parameters of a greenhouse on a regular basis round the clock for cultivation of crops or specific plant species which could maximize their production over the whole crop growth season and to eliminate the difficulties involved in the system by reducing human intervention to the best possible extent. The system comprises of sensors, Analog to Digital Converter, microcontroller and actuators.
When any of the above mentioned climatic parameters cross a safety threshold which has to be maintained to protect the crops, the sensors sense the change and the microcontroller reads this from the data at its input ports after being converted to a digital form by the ADC. The microcontroller then performs the needed actions by employing relays until the strayed-out parameter has been brought back to its optimum level. Since a microcontroller is used as the heart of the system, it makes the set- up low-cost and effective nevertheless. As the system also employs an LCD display for continuously alerting the user about the condition inside the greenhouse, the entire set-up becomes user friendly.
Thus, this system eliminates the drawbacks of the existing set-ups mentioned in the previous section and is designed as an easy to maintain, flexible and low cost solution.
2. SYSTEM MODEL
2.1 BASIC MODEL OF THE SYSTEM
2.2 PARTS OF THE SYSTEM:
i. Sensors (Data acquisition system) a. Temperature sensor (LM35) b. Humidity sensor (HH10D)
c. Light sensor (LDR)
d. Moisture sensor
ii. Analog to Digital Converter (ADC 0808/0809)
iii. Microcontroller (AT89S52)
iv. Liquid Crystal Display (Hitachi's HD44780)
v. Actuators – Relays
vi. Devices controlled
a. Water Pump (simulated as a bulb)
b. Sprayer (simulated as a bulb)
c. Cooler (simulated as a fan)
d.Artificial Lights (simulated as 2 bulbs)
2.2.1 TRANSDUCERS (Data acquisition system):
This part of the system consists of various sensors, namely soil moisture, humidit y, temperature and light. These sensors sense various parameters- temperature, humidity, soil moisture and light intensity and are then sent to the Analog to Digital Converter.
2.2.2 ANALOG TO DIGITAL CONVERTER (ADC):
The analog parameters measured by the sensors are then converted to corresponding digital values by the ADC.
The microcontroller is the heart of the proposed embedded system. It constantly monitors the digitized parameters of the various sensors and verifies them with the predefined threshold values and checks if any corrective action is to be taken for the condition at that instant of time. In case such a situation arises, it activates the actuators to perform a controlled operation.
An array of actuators can be used in the system such as relays, contactors, and change over switches etc. They are used to turn on AC devices such as motors, coolers, pumps, fogging machines, sprayers. For the purpose of demonstration relays have been used to drive AC bulbs to simulate actuators and AC devices. A complete working system can be realized by simply replacing these simulation devices by the actual devices.
2.2.5 DISPLAY UNIT:
A Liquid crystal display is used to indicate the present status of parameters and the respective AC devises (simulated using bulbs). The information is displayed in two
modes which can be selected using a push button switch which toggles between the modes. Any display can be interfaced to the system with respective changes in driver circuitry and code.
2.3 STEPS FOLLOWED IN DESIGNING THE SYSTEM:
Three general steps can be followed to appropriately select the control system:
Step #1: Identify measurable variables important to production.
It is very important to correctly identify the parameters that are going to be measured by the controller’s data acquisition interface, and how they are to be measured.
The set of variables typically used in greenhouse control is shown below:
Sl. No. Variable to be monitored Its Importance
1 Temperature Affects all plant metabolic functions.
2 Humidity Affects transpiration rate and the plant's thermal
3 Soil moisture Affects salinity, and pH of irrigation water
4 Solar Radiation Affects photosynthetic rate, responsible for most
thermal load during warm periods
Table 2.1 Importance of the various parameters
An electronic sensor for measuring a variable must readily available, accurate, and reliable and low in cost. If a sensor is not available, the variable cannot be incorporated into the control system, even if it is very important. Many times variables that cannot be directly or continuously measured can be controlled in a limited way by the system. For example, fertility levels in nutrient solutions for greenhouse production are difficult to measure continuously.
Step #2: Investigate the control strategies.
An important element in considering a control system is the control strategy that is to be followed. The simplest strategy is to use threshold sensors that directly affect actuation of devices. For example, the temperature inside a greenhouse can be affected by controlling heaters, fans, or window openings once it exceeds the maximum allowable limit. The light intensity can be controlled using four threshold levels. As the light intensity decreases one light may be turned on. With a further decrease
in its intensity a second light would be powered, and so on; thus ensuring that the plants are not deprived of adequate sunlight even during the winter season or a cloudy
More complex control strategies are those based not only on the current values of the controlled variables, but also on the previous history of the system, including the rates at which the system variables are changing.
Step #3: Identify the software and the hardware to be used.
It is very important that control system functions are specified before deciding what software and hardware system to purchase.
The model chosen must have the ability to:
1. Expand the number of measured variables (input subsystem) and controlled devices (output subsystem) so that growth and changing needs of the production operation can be satisfied in the future.
2. Provide a flexible and easy to use interface.
3. It must ensure high precision measurement and must have the ability resist noise.
Hardware must always follow the selection of software, with the hardware required being supported by the software selected. In addition to functional capabilities, the selection of the control hardware should include factors such as reliability, support, previous experiences with the equipment (successes and failures), and cost.