2010 International Symposium on Electronic System Design
Microcontroller based Polyhouse Automation Controller
G.K. Banerjee
Rahul Singhal
Electrical engineering dept., College of Technology
G B Pant University
Pantnagar, India
gkb_1947@yahoo.co.in
Electrical engineering dept., College of Technology
G B Pant University
Pantnagar, India
rahulsinghal@gbpuat-tech.ac.in
Abstract — In this paper a method for the control of
temperature and relative humidity inside a polyhouse using
microcontroller has been discussed. In the proposed method,
the greenhouse controller senses the change in temperature
and relative humidity with the help of input sensors and
process the output to take appropriate control action. The
proposed system is a low cost and user friendly system with
high stability and reliability.
Keywords – microcontroller based controller; intelligent
polyhouse; polyhouse farm environment management; single
chip microcomputer.
Relative
Humidity
Sensor
I.
INTRODUCTION
A polyhouse is a metal structure covered with polythene
It is an automation industry which is developing very rapidly
with a trend of shifting towards low cost, reliable in
operation, stable in design and user friendly control system.
The microcontroller based system provides a good platform
for designing the polyhouse automation controller for a
single unit. This makes a control system affordable, reliable
in operation, easy to reprogram. It ensures the upgradation
even in the working mode and provides low maintenance
solution for polyhouse, especially in rural areas for the
farmers having small lands [1].
The proposed system is a central one host system which
is used in automating the data acquisition process of the
various climatic parameters that governs the plant growth
and allows information to be collected at the high frequency
with the less labor requirements. The proposed methodology
of farming reduces dependency on rainfall and makes the
optimum use of land and water resources [2]. However, the
farmers must be provided with the expert guidance so that
they can use this new technology of polyhouse farming
properly.
II.
PIC
16F877A
Microcont
roller
Relay
Operat
ing
Circuit
Heating
Pipes
Exhausts
Sprinklers
Fig.1 General Structure of polyhouse automation controller
2) Signal collection: Signal collection includes analog
signal collection from temperature and relative humidity
sensor, analog to digital conversion and manipulations by
microcontroller.
3) Control processing by system software: It consist of
the real-time monitoring of the parameters through sensors
and controlling the parameters prevailing inside the green
house by generating actuating signal either to switch ON or
to switch OFF the heating pipes (in which hot water flows
into the pipe used for heating), sprinklers and exhausts.
B. System working principle
The TEMP and RH are the digital values obtained after
the conversion of the analog signals from the temperature
and relative humidity sensors. TMAX and TMIN define the
desired operating range of temperature in polyhouse. The
RHMIN is the lower limit of operating range of the relative
humidity in polyhouse. The average temperature TAVG is
calculated in order to restrict cooling and heating action.
GENERAL STRUCTURE DESIGN
A. General structure design of the polyhouse automation
controller consist of
1) Two levels structure: The polyhouse automation
controller was build with two levels. The first level is located
outside the polyhouse consisting of LCD panel, switches and
relay circuit. The second level is located in the polyhouse
consisting of microcontroller, temperature and relative
humidity sensors.
978-0-7695-4294-2/10 $26.00 © 2010 IEEE
DOI 10.1109/ISED.2010.38
LCD Display
Temper
ature
Sensor
TAVG = (TMAX + TMIN) / 2
(1)
In this system, we have used the Microchip PIC16F877A
microcontroller which is inbuilt with a 10 bit analog to
digital (AD) converter with 8 channels. CMOS technology
is being used for designing the Flash / EEPROM memory of
158
The relative humidity sensor ensures the accuracy of ±
5% within its full range of 30% to 90%. The signals obtained
from sensors do not require the signal conditioning as they
are large enough to be converted to digital values by AD
module. The microcontroller PIC16F877A analyses the
digital data by the help of the system software and generates
the actuating signal to the relay circuitry to switch ON the
sprinklers, exhausts and heating pipes, in order to control the
environment parameters of polyhouse [6].
We must have stable Vref+ to AD module for accurate and
precise conversion.
microcontroller. It ensures a very low-power consumption,
fully static design, high speed operation and wider operating
range (2.0V to 5.5V) that is they are excellent to use when
operating on a battery. Large EEPROM data memory on
microcontroller (256 x 8 bytes with 1,000,000 erase / write
cycle) helps in saving the various data in non volatile
memory which would be available to the microcontroller
even if the power supply is interrupted. The user needs not
to enter (RHMIN, TMAX, TMIN) again and again after each
power supply interruption [3]. It communicates with the
temperature and relative humidity sensors in real time in
order to control the temperature and relative humidity inside
the polyhouse. It gives actuating signals to relay circuit
which helps in switching exhausts, heating pipes and
sprinklers respectively according to the necessity of the
desired crop. An integrated liquid crystal display (LCD) is
used for real time display of data acquired from temperature
and relative humidity sensors and the ON status of the
sprinkler, heating pipes and exhausts [4-5].
Vref+
III. HARDWARE DESIGN
The temperature and relative humidity are the parameters
controlled by the microcontroller based polyhouse
automation controller. Temperature sensor (LM35DZ) and
relative humidity sensor (BHS220M) gives the analog signal
to the analog input port of the microcontroller. A 10 bit
analog to digital converter which is inbuilt in the
microcontroller converts them to digital value. The
temperature sensor (LM35DZ) ensures the accuracy of ±
0.75 °C within its full range from 2 °C to 150 °C. For the
measurement of relative humidity, a capacitive sensor has
been used. The sensor consists of a metal electrode, a coated
glass substrate and a polymer layer placed between the two.
The permittivity of the dielectric (polymer) depends on the
relative humidity. For an optimal humidity exchange
between the polymer layer and the surrounding air, the metal
electrode is a porous layer of 0.1 to 1µm produced by the
special process. The absence of additional insulation layer
leads to the high sensitivity of the sensor. The relationship
between the capacitance of the sensor and the relative
humidity is expressed as
CRH =  Є0ЄRH 



Fig. 2 Pre regulator Circuit for precise Vref+
For the conversion of 5mV equivalent to 1 bit, we must
have the Vref+ as
5mV = Vref+ / 210
(for 10 bit AD module)
Vref+ = 5mV * 210
= 5.12 V
(3)
AD module requires 150µA from Vref+. The voltage
output of the pre regulator circuit comprising of zener diodes
will not be affected as it is operating at higher current.
IV.
CONTROL ACTION
The controlled action is being designed to take the care
of discontinuous and abrupt changes in the analog signal
from the sensors. It is designed for a range in which control
action will either switch ON or switch OFF the exhausts,
heating pipes and sprinklers.
In order to initiate the control action, initially AD
converter is set for temperature. The microcontroller puts
the delay of a half a second. Afterwards it calls for the AD
conversion for the relative humidity again keeping the same
delay.
Control algorithm followed by the system software in
PIC16F877A microcontroller is as shown in the figure 5.

Where
CRH is the capacitance at relative humidity RH
Є0is the absolute permittivity
ЄRH is the permittivity of the dielectric depending on
humidity (ЄRH = 3 at 0% RH and 3.9 at 100% RH)
A is the area of the electrodes
d is the distance between the electrodes
159
Heating Pipes Status
The controller checks which limit of temperature is
violated, if lower limit TMIN is crossed that is if the
temperature prevailing in the polyhouse is less than the TMIN
then the heating action is taken by heating pipes till the
temperature increases enough and crosses the TAVG.
Actuating signal generated by system software for heating
pipes with respect to temperature as shown in figure 4.
OFF
ON
0
10
20
30
TAVG
TTMIN
MIN T
AVG TT
MAX
MAX
40
Temperature
Fig.4 Heating Pipes Status Vs Temperature
If the upper limit TMAX is exceeded that is if the
temperature prevailing inside the polyhouse is greater than
that of TMAX then cooling action is being performed by the
exhausts till the temperature decreases enough and reaches
the TAVG. Actuating signal generated by system software for
exhausts with respect to temperature as shown in figure 5.
Fig. 5 Exhausts Status Vs Temperature
After that controller then checks for the relative humidity
lower limit is violated that is the relative humidity
prevailing in polyhouse is lower than that of the RHMIN. If it
is so then the sprinklers are switched on to attain the level
back till it is incremented by 10% above the RHMIN.
Actuating signal generated by system software for sprinklers
shown in figure 6.
Fig.3 Control algorithm followed by the microcontroller
160
Fig.6 Sprinkler Status Vs Relative Humidity
Control Action is being repeated again and again after a
time delay of one second by the system software in the
microcontroller.
Fig. 7 showing the Temperature below TMIN and control status
VI.
V. SYSTEM SOFTWARE DESIGN
The temperature and relative humidity are the parameters
monitored and controlled by the controller. As the 10 bit AD
module is inbuilt in microcontroller simplifies the all over
design. The data obtained needs manipulation to get the
actual value of temperature and relative humidity. The
system works in two modes.
POSSIBLE ENHANCEMENT
As we level up we have the central control unit which
will receive the data through CAN from the microcontroller
installed in the polyhouse. The control action will be
performed by the central control unit, by providing the
actuating signal to the microcontroller which will take
necessary action inside the desired polyhouse.
A. Internetworking of the various polyhouse
Various polyhouses can be controlled together if they are
connected through CAN. This will help in exchange of
information between polyhouses and the central control
unit. In central control unit actual value of different
parameters inside the polyouse will be saved periodically.
After completion of life cycle of the crop, actual parameter
variation will be compared to the desired range. This
comparison will help in drawing important conclusion
regarding that crop.
A. System Software in initializing mode
In this mode first of all, the ports of the microcontroller
are configured according to the hardware connections. Then
the predefined values of temperature range as TMIN and TMAX
along with the RHMIN is being displayed on the LCD screen
for a second it automatically shifts to the working mode.
B. Web networking of the central control unit
We can make our system more users friendly and easy to
access by connecting the central control unit with the web.
Then polyhouses can be monitored and controlled through
TCP/IP anywhere in the world.
C. Other parameter control
Several other parameters such as light, soil PH, CO2 etc.
can be added for precise control over the yield and quality
of the crop planted in the polyhouse.
D. Full automation with robotics
The robots can be controlled through the central control
unit. The main advantage of the robots would be to prevent
human contamination and ensures careful nursing of the
plants.
Fig. 6 displaying the predefined values on LCD
B.
Visual control by system software in working mode
In this mode the real time values of temperature, relative
humidity and ON status of the sprinkler, heating pipes and
exhaust will be refreshed and displayed on LCD screen by
the system software.
VII. CONCLUSION
Intelligent polyhouse is an effective way to reduce labor
cost, fertilizer cost, water resources and to increase the
161
productivity of the plants on the small land holding. It is
boon to farmers with small land in their hand for cultivation.
Low cost and power polyhouse automation controller can be
achieved by using PIC16F877A microcontroller which
provides a very simple design with affordable and reliable
control action. The scheme employs LCD operation making
the system user friendly and can be easily understood by the
farmers. Moreover it is not restricted to a particular plant
type or specific temperature and humidity ranges as the
PIC16F8877A is easy to reprogram. It operates at high speed
(Max 20 MHz clock input) which ensures faster execution of
the codes, essential for the real time interaction with the
environment.
The objective of the project is to design an autonomous
control for temperature and relative humidity in a close
environment of the single polyhouse unit.
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