Designing an IoT Smart Outlet that Can Monitor

Study Case Designing an IoT Smart Outlet that Can Monitor and Protect Against Overload and High Temperatures Michael Kurniawan (2018123456) University of Cincinnati, 2600 Clifton Ave, Cincinnati, OH 45221, United States kurniaml@mail.uc.edu Abstract The installation of electrical outlets in electrical systems is very important because most electrical equipment is activated through these outlets. The use of various types of electrical loads on a single outlet can cause an increase in temperature at the terminals, accelerating damage and even posing a fire risk due to the rise in conductor terminal temperature. Outlets not only function as power connectors, but can also be developed as devices to monitor the electrical power and energy used, as well as terminal temperatures remotely. This outlet monitoring and protection system is designed by adding hardware and software capable of detecting load power and terminal temperature changes in real time. The main component of this system is the NodeMCU ESP8266 module, which has Wi-Fi features and supports open-source IoT platforms. NodeMCU is connected to a DHT22 temperature sensor and a PZEM-004 power sensor. NodeMCU is programmed with instructions so that the signals received from the sensors can be converted into numerical data that is easy for users to understand. The readings are displayed on an LCD and sent via the internet to the user's smartphone using the Blynk application. Test results show that this IoT-based outlet system is capable of accurately displaying information on electrical power usage and outlet terminal temperature. The average power reading error on the PZEM-004 sensor is around 3.5%, while the average temperature reading error on the DHT22 sensor is only 0.3%. The system will automatically cut off the electrical current if the power exceeds 500 W or the terminal temperature exceeds 50°C. Keywords: Electrical outlet, IoT, NodeMCU ESP8266, PZEM-004, DHT22 MICHAEL KURNIAWAN 1 Study Case INTRODUCTION According to Merriam-Webster Dictionary, an electrical outlet is a place to connect electrical current to electrical or electronic devices. The main function of an outlet is as a power distribution point that allows various household, office, and industrial appliances to obtain electricity supply. In general, an outlet consists of two metal terminals that function as contacts for plugs and are encased in plastic insulating material. In residential, building, and industrial electrical systems, outlets are components used to connect electrical loads to the main power source. Variations in the type and capacity of electrical loads connected can cause an increase in temperature at the metal terminals, which has the potential to accelerate damage or even trigger a fire [1]. The use of electrical equipment that does not meet the National Electrical Code (NEC) standards can accelerate the degradation of electrical components and cause short circuits, which can result in fires [2]. The development of smart outlet systems is not new. Various types of smart plugs are available on the US market that allow users to control power remotely using a smartphone. However, most of these products only focus on remote ON/OFF functions. Previous research has expanded the meaning of smart outlets to include devices that can not only be controlled but also function as IoT-based energy monitoring systems. Fahrudin Nur Iksan and Gunawan Tjahjadi (2018) developed a system capable of remotely monitoring current and temperature via the internet, even though the device did not take the form of a physical outlet [3]. Shelsa Foiqotul Himmah et al. (2018) designed a smart outlet capable of classifying the types of electrical devices connected using the Naive Bayes algorithm [5]. Aldiansyah Famni Saputra et al. (2019) introduced an Arduino-based smart outlet through ResearchGate that emphasizes automation for household energy efficiency [6]. Doly Handali and Jefri Lianda also developed an IoT-based electrical power monitoring system capable of detecting load current and voltage, but it does not yet include terminal temperature detection and automatic protection features [7]. Tanto and Darmuji researched the use of IoT in electrical energy monitoring devices with data display on LCD, but without remote monitoring integration via smartphone [8]. MICHAEL KURNIAWAN 2 Study Case METHOD This smart outlet system uses NodeMCU ESP8266 as the main microcontroller connected to the internet network. Thus, information about the power and temperature of the terminal can be monitored remotely through the Blynk application on a smartphone. In addition, the system also allows users to control the ON/OFF status of electrical devices remotely. A. System Design and Main Components The system consists of two main sensors, namely the DHT22 temperature sensor and the PZEM-004 power sensor (see Figure 1). The power sensor measures two main variables: voltage and current, which are then used to calculate the actual electrical power. Figure 1. Block diagram of the IoT-based smart outlet system B. DHT22 Temperature Sensor The DHT22 sensor is a high-accuracy temperature and humidity sensor with a digital signal output. This sensor has been factory calibrated and has room temperature compensation stored in its internal memory (OTP). The DHT22 can transmit data up to a distance of 20 meters, but if the cable length exceeds 2 meters, a 0.33 μF capacitor is required between the VCC and GND pins on the NodeMCU to maintain signal stability. Figure 2. DHT22 temperature sensor DHT22 specifications [9]: • Operating voltage: 3.3 – 6 VDC MICHAEL KURNIAWAN 3 Study Case • Communication: Single-wire two-way serial • Temperature range: -40°C to 80°C • Humidity range: 0 – 100% RH • Accuracy: ±2°C (temperature), ±5% RH (humidity) C. Programming the DHT22 Sensor The program code utilizes the OneWire.h and DHT.h libraries. The sensor is connected to the GPIO 0 digital pin on the ESP8266. Program Code 1. Initialize the DHT22 sensor #include #include #define DHTPIN 0 #define DHTTYPE DHT22 DHT dht(DHTPIN, DHTTYPE); The sensor is activated in the setup() function with the command: void setup() { dht.begin(); Wire.begin(); } The temperature reading process is repeated in loop() and the results are sent to the Blynk application: void loop() { float temperature = dht.readTemperature(); Blynk.virtualWrite(V21, temperature); } D. PZEM-004 Power Sensor The PZEM-004T power sensor can measure AC voltage (80–260 V), current (up to 100 A), real power, energy, frequency, and power factor (cos θ). This sensor is compatible with various microcontroller boards such as Arduino, ESP8266, and Raspberry Pi. MICHAEL KURNIAWAN 4 Study Case Figure 3. PZEM-004 power sensor There are three types of electrical power: real power (P), apparent power (S), and reactive power (Q), which form a power triangle (see Figure 4). Figure 4. Power triangle diagram Formulas: 𝑃 = 𝑉 × 𝐼 × cos⁡ 𝜃(1) 𝑆 = 𝑉 × 𝐼(2) 𝑄 = 𝑉 × 𝐼 × sin⁡ 𝜃(3) Explanation: P = Real power (Watts) S = Apparent power (Volt-Amperes) Q = Reactive power (VAR) V = AC voltage (Volts) I = Current (Amperes) θ = Phase angle cos θ = Power factor Power sensor initialization is performed using the SoftwareSerial.h and PZEM004Tv30.h libraries: #include #include PZEM004Tv30 pzem(12,13); MICHAEL KURNIAWAN 5 Study Case E. Solid State Relay (SSR) SSR is a semiconductor-based electronic switch used to control electrical loads without mechanical contact. SSR uses an optocoupler for isolation between the DC control circuit and the AC load circuit. Figure 5. Internal diagram of SSR When the control signal is logic high (+5V), the photo-diode triggers the triac so that current flows between terminals T1 and T2. In this study, the OMRON G3MB module was used, which is capable of handling currents up to 2 A with a maximum AC voltage of 240 V. Figure 6. OMRON G3MB SSR module F. System Integration and Complete Circuit The temperature sensor and power sensor are connected to the NodeMCU ESP8266, which acts as the system control center. NodeMCU sends data to the Blynk application via the internet, displays readings on the LCD, and controls the SSR based on power and temperature thresholds. If the load power exceeds 500 W or the terminal temperature reaches 50°C, the system automatically cuts off the electrical current to prevent damage and fire. MICHAEL KURNIAWAN 6 Study Case Figure 7. IoT-based smart outlet system circuit RESULTS AND DISCUSSION Figure 8 shows the physical appearance of the interior of the smart power outlet system. The figure shows a number of electronic modules connected to the ESP8266 MCU IoT module, all packaged in a box measuring 4 × 12 × 8 cm³. Figure 9 shows the top of the outlet device. The image shows an outlet equipped with an LCD screen that displays electrical information such as load power, electric current, power factor, and AC voltage. The device also has two LED indicators, one red and one yellow. • The red LED indicates the Wi-Fi network connection status. • The yellow LED indicates the status of the manual switch on the outlet. If the red LED flashes slowly (glowing and fading gradually), it means that the device has successfully connected to the network. However, if the red LED flashes rapidly (blinking), it means that the connection to the network has failed. Meanwhile, the yellow LED turns on when the switch is active (ON) and turns off when the switch is disconnected (OFF). Figure 8. Internal circuitry of the smart outlet system. MICHAEL KURNIAWAN 7 Study Case Figure 9. Physical appearance of the IoT outlet. The LCD screen in Figure 9 displays real-time electricity usage data. In the example display, the readings show: • 52.60 W of electrical power, • 225.10 V of AC voltage, • 0.31 A of load current, and • a power factor of 0.76. These values will change according to variations in the electrical load used. This information can also be monitored through the Blynk application on a smartphone, as shown in Figure 10. The Blynk screen shows: • ON/OFF button (yellow square icon), • AC voltage 240.00 V, • Power factor 0.9, • Current 1.46 A, • Frequency 50 Hz, • Energy consumption 86.432 kWh, • Temperature 34.0°C, and • Load power 347.0 W. This system is also capable of sending automatic alerts to users in the event of abnormal conditions, such as increased temperature or power usage exceeding safe limits. MICHAEL KURNIAWAN 8 Study Case Figure 10. Blynk application interface display on a smartphone. A. Temperature Sensor Testing The temperature of the outlet terminal can increase during use due to several factors, including: • Non-standard plug and terminal quality, • Excessive load usage, • Excessive number of connected devices, and • Cable installation errors. Excessive temperature increases can cause sparks and potentially lead to fires. The purpose of the temperature sensor test is to assess the sensor's response to temperature increases at the outlet terminal. The heat source used is a halogen lamp placed near the terminal. Measurements are taken using a digital thermometer and the results are compared with readings from the Blynk application on a smartphone. Table 1. Results of temperature increase measurements at the outlet terminal. MICHAEL KURNIAWAN 9 Study Case A comparison between the readings from the digital thermometer and the smartphone application shows an average difference of only 0.3%, well below the tolerance limit of 5%. This proves that temperature monitoring via a smartphone provides accurate and reliable results. In addition, the system also has an automatic protection feature. If the terminal temperature exceeds 50°C, the outlet will automatically cut off the electrical current, the alarm buzzer will sound, and a warning will appear on the LCD screen saying “WARNING: TEMPERATURE PROTECTION ACTIVATED,” as shown in Figure 11. Figure 11. Overheating protection indicator display. MICHAEL KURNIAWAN 10 Study Case B. Power Sensor Testing The power sensor uses the PZEM-004 module as shown in Figure 12. This sensor functions to measure the actual power (real power) of the connected load. Figure 12. Electrical power sensor circuit. The sensor works by detecting the load current through a current transformer (CT) and measuring the AC voltage. The TX and RX terminals are connected to the serial communication pins on the main outlet module (see Figure 6). The actual power is calculated using the formula: 𝑃 = 𝑉 × 𝐼 × cos⁡ 𝜙 where: P= actual power (W), V= AC voltage (V), I= load current (A), Cos ϕ= power factor. Power readings are compared between a digital wattmeter, the outlet's LCD display, and the smartphone display. Figure 13 shows an example of readings from a wattmeter at 214 W and a smartphone at 212.6 W. Figure 13. Power readings on the wattmeter and the Blynk app. MICHAEL KURNIAWAN 11 Study Case Table 2. Power sensor test results for various types of loads. The results show relatively small differences between readings from the wattmeter and LCD outlet. At low loads, the error rate is greater than at high loads. For example: • Neon lights show a deviation of about 18%, • LED lights about 10%. This is due to the internal electronic circuitry of the lights affecting the measurement results. For soldering and electric grinder loads, the difference in values occurs because the loads were not operated at maximum power during testing. Overall, the average power reading error is 3.5%, indicating that the power sensor provides near-accurate results. Factors causing deviation include load characteristics (inductive or capacitive) and measurement device resolution limitations (wattmeter does not display decimal numbers). Despite minor variations, power changes are consistently detected on the LCD and smartphone. If the power exceeds 500 W, the system will automatically activate a buzzer alarm and display a message on the LCD: “WARNING: POWER OVERLOAD PROTECTION ACTIVATED” as shown in Figure 14. MICHAEL KURNIAWAN 12 Study Case Figure 14. Overload protection display on the LCD. This IoT-based smart outlet uses a Solid State Relay (SSR) with a maximum current limit of 2 A, so the safe load capacity is around 440 W. However, testing shows that the device can still withstand greater power for a short time, although this is not recommended for long-term use. CONCLUSION 1. The IoT-based smart outlet system functions well as designed. 2. The outlet can be controlled manually (via physical buttons) or remotely via a smartphone. 3. The average difference in temperature readings between the digital thermometer and the smartphone app is 0.3%. 4. The average power reading difference between the wattmeter and the smartphone is 3.5%. 5. The system provides an overload warning when consumption exceeds 500 W. 6. The system provides an overheating warning when the terminal temperature (copper conductor) exceeds 50°C. MICHAEL KURNIAWAN 13 Study Case REFERENCE MICHAEL KURNIAWAN 14