## 2 Materials and Methods
### Hardware
#### 2.1.3 ESP32 Microcontroller and Communication Protocols  
The ESP32 Microcontroller, is a series of low-cost, low-power SoC (System on Chip) microcontrollers designed and developed by the company, Espressif Systems. It is a feature-rich microcontroller with a variety of integrated peripherals for a wide range of applications. The ESP32 series employs two cores, 32-bit Tensilica Xtensa LX6 CPU, 448 KB ROM memory, 520 KB RAM memory, 4 MB flash memory, standard 802.11 b/g/n Wirelesscommunication card, 2.4 GHz, built-in antenna on the board, STA/AP/STA+AP operation modes, Bluetooth BLE 4.2, and peripheral interface (GPIO, ADC, Hall sensor, DAC, UART, I2C, I2S, SPI, PWM); it can individually operate at a frequency of up to 240 MHz [39]. Due to compatibility and features, this microcontroller is featured in several projects. For example, [PERSON] and [PERSON] [40] propose system monitoring for low-cost automated solar pumping for irrigation in developing countries, [PERSON] et al. [41] proposed the development of a robotic arm for use in the operating room, which is controlled by joystick from anywhere, and [PERSON] et al. [42] proposed the implementation of a smart fuel station in the fueling process using Internet of Things (IoT) technology. [PERSON] and [PERSON] [43] proposed a smart surveillance system, and [PERSON] et al. [44] proposed a biosensor coupled to ESP32-Webserver capabilities for continuous point-of-care oxygen saturation and heartrate monitoring. A Universal Asynchronous Receiver Transmitter (UART) communication is a serial communication system, i.e., bit sequences. It uses only two signal lines (RX, TX) to complete full-duplex communication. To establish communication, a bit sequence consisting of start bit, data bit, parity bit and stop bit is required. The ESP-NOW communication protocol [45] is a fast communication protocol that can be used to exchange small messages. It was developed by Espressif and allows multiple devices to communicate without using Wi-Fi. The protocol is similar to the low-power 2.4 GHz wireless connectivity that is usually deployed in wireless mice and has a transmission rate of 1 Mbps. ESP-NOW applies IEEE 802.11 technology, along with IE function developed by Espressif and encryption technology CCMP (Counter Mode with Cipher Block Chaining Message Authentication Code Protocol), to provide a secure, Wi-Fi-conectionless communication solution. The ESP-NOW protocol presents the following features: encrypted and unencrypted unicast communication, 250 bytes storage, and return function that can be set to inform the application layer about the success or failure of the transmission. It is unable to support Broadcast, but in station mode, it can support up to 10 devices in encrypted pairs and up to 20 unencrypted pairs, including encrypted pairs. To establish accurate communication, it is necessary to register both devices with the following data: media access control (MAC) address, channel number (0-15) and information on whether the data are encrypted or not. This communication protocol is very versatile and allows one-way or two-way communication in different configurations. The I2C-Inter-Integrated Circuit is a communication protocol with a two-wire interface (SDA-serial data and SCL-serial clock) used to establish synchronous serial communication between a master and one or more slave devices. To establish this communication, the device generates the clock signal for the following bit sequences: one bit for communication start condition, seven address bits, one bit for read/write (R/W), two ACK/NACK bits-acknowledge/not acknowledge (0/1), and one bit for communication end. Normally, I2C allows communication between 128 devices (2\({}^{n}\), \(n\) being the number of address bits). The addresses (0 to 127) should never be duplicated, and the devices operate at a normal frequency of 100 kbit/s. The above-mentioned communication protocols were used in this study for the following purpose:  
1.