Development of an Intelligent Greenhouse Temperature Control System

Study Case Development of an Intelligent Greenhouse Temperature Control System Using the AT89S51 Microcontroller Michael Kurniawan (2018123456) University of Cincinnati, 2600 Clifton Ave, Cincinnati, OH 45221, United States kurniaml@mail.uc.edu Abstract The automatic temperature control system in a greenhouse is a microcontroller-based room temperature control application designed to automatically maintain a stable microclimate. This system uses several types of sensors as sensing elements and a number of actuators as cooling and heating systems. The AT89S51 microcontroller acts as the control center, where the room temperature is automatically regulated based on sensor data. A 220-volt, 300-watt heater is used as the heating element, while the LM35 sensor detects the room temperature. Two fan units are used as actuators to regulate hot air circulation. With the implementation of an effective control system, sensors and actuators can work together to maintain temperature stability inside the greenhouse. Keywords: automatic control, temperature, LM35 sensor, microcontroller INTRODUCTION Along with technological advances in the United States, various devices and systems are now largely controlled automatically. Examples include automatic street lighting systems, product selection processes in manufacturing industries that use conveyor belts, and various other automation applications. The application of this automation technology aims to ease human work while increasing efficiency and effectiveness in terms of time, energy, and costs. This research focuses on the design of an Automatic Greenhouse Temperature Control System, as this type of technology has significant benefits, especially in the field of modern agriculture. In various regions, many plant species require specific environmental conditions to grow optimally. Therefore, automatic temperature control MICHAEL KURNIAWAN 1 Study Case is important to support the preservation and intensive cultivation of plants. In an automatic control system, the main device that acts as the control brain can be a microcontroller, Programmable Logic Controller (PLC), or Personal Computer (PC). In this study, an AT89S51 microcontroller was used as the main control unit to automatically regulate the temperature in the greenhouse, replacing the inefficient manual control. RESEARCH OBJECTIVES The objectives of the design and development of the system entitled “Automatic Greenhouse Temperature Control” are as follows: 1. To learn and understand the process of temperature control using a microcontroller. 2. To study automation systems and room temperature control mechanisms using sensors and simple electronic circuits. PROBLEM LIMITATIONS To keep the discussion focused on the main objectives, this research has the following problem limitations: 1. The AT89S51 microcontroller is used as the main controller in this system. 2. The ADC0804 converter IC functions to convert analog input signals into digital signals that can be read by the microcontroller. 3. The discussion focuses on the temperature sensor, humidity sensor, and relay components as load controllers. 4. The analysis covers control circuits for direct current (DC) motors and alternating current (AC) motors. 5. The software used in this system is written in assembly language. METHOD In designing the Automatic Greenhouse Temperature Control system, this system is divided into two main parts based on the working principle and components used, namely system input design and system output design. System Input Design MICHAEL KURNIAWAN 2 Study Case ADC0804 (Analog to Digital Converter) The analog to digital converter (ADC) used in this system is a Successive Approximation ADC. In the ADC0804, the conversion process starts from the most significant bit (MSB) in the register, then the conversion result is compared using a comparator. If the analog input voltage is greater than the reference voltage, the bit is set to “1”; otherwise, if it is smaller, the bit is set to “0”. The ADC0804 has one analog channel and eight digital channels connected to Port 3 of the AT89S51 microcontroller. The ADC0804 consists of 256 ladder resistors that function as voltage dividers and are controlled by the Successive Approximation Register (SAR) to produce an estimated voltage. The process works as follows: 1. The first approximation is made on the most significant bit with a binary value of 10000000, so that the switch tree produces a voltage of: 𝑉= 128 × 5𝑉 = 2.5𝑉 256 The 5V voltage is obtained from the difference between the positive reference voltage (5V) and the negative reference voltage (0V). 2. At the end of the first cycle, the SAR checks the comparator output. If the input voltage (Va) is greater than or equal to the estimated voltage (Vo), the SAR sets the first bit to “1”, and that value is used for the next calculation. 3. If Va < Vo, then the SAR gives a value of “0” and the Va value remains the same as before. 4. The next process continues to the second bit with binary 01000000, resulting in: 𝑉= 64 × 5𝑉 = 1.25𝑉 256 To generate a clock signal on the ADC0804, a resistor R = 10 kΩ and a capacitor C = 100 pF are used, so that the oscillator frequency is calculated using the formula: 𝐹= 1 1 = = 6.06 kHz 1.1 × 𝑅 × 𝐶 1.1 × 104 × 100 × 10−12 The microcontroller's operating frequency is 758 kHz, which is suitable for the requirements of this control system. MICHAEL KURNIAWAN 3 Study Case AT89S51 Microcontroller The main circuit of the minimum system consists of four I/O lines. Pins 1–8 (Port 1.0–1.7) are used as signal inputs from the ADC0804. The system block includes: 1. Microcontroller as the control center, 2. Motor driver, and 3. Actuators in the form of DC motors and fans. Sensors and limit switches function as microcontroller inputs. Port 0 and Port 1 are used as outputs to drive the actuator through the driver circuit. Both input and output signals use TTL logic, allowing them to be directly processed by the microcontroller according to the pre-programmed temperature control system. System Output Design Fan and Exhaust Control Circuit When the LED cathode input on the Opto-Coupler (Input 1) receives logic “0”, the transistor inside the Opto-Coupler activates, allowing current to flow from the collector to ground. The voltage across the 10 kΩ resistor activates the MOSFET gate, causing the MOSFET to conduct (acting as a closed switch). Current flows from the 12V source through the fan to ground, inducing electromagnetic induction in the fan coil so that the fan rotates. To change the direction of fan rotation, Input 2 on the Opto-Coupler is given logic “0”. This activates another transistor and turns on the relay coil. Induction in the relay generates a magnetic field that moves the relay contact position from normally closed (NC) to normally open (NO), thereby changing the direction of fan rotation. Heater Control Circuit When the LED cathode input from the Opto-Coupler is logic “0”, current flows through the LED to the input pin that functions as ground. The Opto-Coupler transistor is active and conducts current from the collector to ground, inducing a voltage across the 10 kΩ resistor. This voltage functions as the gate voltage for the MOSFET, causing it to conduct. The current then flows from the 12V source through the relay coil to ground. The electromagnetic induction that occurs in the coil causes the relay to move from the NC (Normally Closed) position to NO (Normally Open), so that the current from the 220V source flows to the heater. The heater then functions as a heater to raise the temperature inside the greenhouse. MICHAEL KURNIAWAN 4 Study Case LCD Circuit The system uses a 16x2 character LCD to display the temperature data read by the LM35 sensor and the results of the system control process. Testing and Data Analysis System testing was conducted to ensure the performance of the device and the accuracy of the sensor readings. Exhaust Circuit Testing Based on the measurement results, when the 12V DC motor is running, the output voltage is 11.8V (logic “1”), while when the motor stops, the output voltage is 0.02V (logic “0”). This result is still within the planned range, which is 10V–12V, so the fan and exhaust control system works as planned. Heater Circuit Testing For the 220V heater circuit, the test results show: Heater active: output voltage = 220V (logic “1”) Heater off: output voltage = 0V (logic “0”) The voltage values are within the tolerance limits (210V–220V), indicating that the heater circuit is working stably and according to design. LM35 Sensor Testing The test results show that the LM35 sensor output voltage increases by 10mV for every 1°C increase, or about 50mV for every 5°C, according to the theoretical characteristics of the LM35 sensor. MICHAEL KURNIAWAN 5 Study Case Analysis of Temperature Change over Time From the experimental data, the average temperature change over time was calculated using the formula: 𝑋change /1°𝐶 = ∑𝑋𝑖 𝑛 The calculation results show that the average temperature change time is approximately ±3 seconds for every 1°C change in temperature. Overall System Testing The LM35 sensor and thermometer were placed in the same temperature environment. The temperature readings on the LCD were compared with the MICHAEL KURNIAWAN 6 Study Case thermometer for 10 minutes, resulting in an average error value: 𝑋error /1°𝐶 = ∑error = 0.0666°𝐶 𝑛 This value indicates that the measurement system has a high level of accuracy with very little deviation. CONCLUSION Based on the results of the design, testing, and analysis, it can be concluded that: 1. The LM35 sensor is an effective choice for temperature measurement because it is affordable, has good linearity, and is easy to integrate with a microcontroller. 2. To ensure even temperature distribution throughout the enclosure, an additional fan is needed for optimal air circulation. The placement of the heater must also be considered to ensure even heat distribution. 3. The component layout design and enclosure shape significantly affect the efficiency of the automatic temperature control system. REFERENCE MICHAEL KURNIAWAN 7 Study Case MICHAEL KURNIAWAN 8