A Universal I²C-to-RS-485 Module for Industrial Sensing

Abstract

Reliable and affordable data acquisition is crucial in industrial applications and critical infrastructure monitoring. However, common low-cost sensors with an I²C interface have limited range and low resistance to interference, which limits their deployment in demanding conditions. This study aimed to design and verify a universal module that bridges the I²C communication interface with the robust RS-485 industrial bus. A hardware module was designed and constructed to serve as a gateway. The core of the system is an STM32F0x1 microcontroller, which controls communication between the local I²C bus, designed to connect a wide range of sensors, and the RS-485 industrial interface. The design emphasizes robustness, including multi-level protection of power and communication circuits. The functionality of the proposed solution was verified by testing the prototype in real conditions. The module, equipped with a combined SHT30 temperature and humidity sensor, was deployed on the premises of the University of Žilina, Slovakia near transport infrastructure. The data collected from two weeks of continuous operation, recorded at ten-minute intervals, confirmed its reliable and error-free functionality. The result of this work is a modular and scalable platform that enables the easy integration of inexpensive sensors into robust industrial networks. This solution significantly reduces the cost and complexity of building distributed monitoring systems in areas such as transportation, industrial automation, and environmental monitoring.

1. Introduction

In globalized, interconnected, and production-dependent economies, transport infrastructure represents a strategic national economic asset, enabling the efficient movement of goods, services, and labor [1,2,3]. Contemporary approaches to constructing and managing transportation systems emphasize key priorities such as safety, operational continuity, economic efficiency, and environmental sustainability. In this landscape, technologies for monitoring and controlling transport networks have assumed an increasingly critical role, with sensors and sensor systems playing a pivotal part. These systems generate the essential data necessary for the optimized and efficient management of transportation processes. Contemporary sensor technologies in transport infrastructure encompass various electronic and mechanical devices, ranging from basic elements to highly advanced sensors integrated within the Internet of Things (IoT) technologies and Artificial Intelligence (AI) systems [4]. In road transport, these sensors furnish data for traffic monitoring systems, environmental parameters, road and sub-base conditions, and for analyzing and evaluating road user behavior [5]. The utilization of sensor networks and intelligent systems is being explored to enhance traffic management and promote seamless urban mobility [6]. From a safety perspective, monitoring current weather conditions is critical, as factors such as frost and ice formation can pose significant risks. Early detection of these conditions enables the provision of effective information to road users while optimizing the deployment of maintenance resources [7]. Moreover, modern sensor systems monitor the current state and predict potentially hazardous situations, contributing to more efficient planning and implementation of transport infrastructure maintenance [8]. This not only yields economic benefits but also has a positive environmental impact. In the context of rail transport, monitoring environmental parameters is essential for preventing deformations and cracks in track and bridge structures, particularly due to extreme temperatures. The data obtained from sensors represents a vital input for contemporary traffic management systems, which increasingly rely on algorithmic AI approaches. These systems can autonomously forecast traffic conditions based on the input data and efficiently manage traffic flows involving large amounts of diverse data [9]. This paper presents the design of a versatile sensor communication module featuring I²C and RS485 interfaces, comprising a printed circuit board and sensors utilizing the I²C protocol. The proposed solution is designed flexibly, enabling standalone operation and integration into a distributed network of measurement nodes. The sensor interface accommodates the connection of diverse sensor types communicating through the standardized I²C protocol. Notably, implementing the SHT30 sensor is given particular attention, as it is designed to measure atmospheric temperature and relative humidity—two fundamental physical parameters directly impacting the safety and functionality of transport infrastructure.

The main contribution and innovation presented in this article is the design, implementation, and practical verification of a universal hardware module that serves as a gateway between a low-cost I²C sensor interface and a robust RS-485 industrial bus. The affordability of I²C sensors is a significant advantage in the development of cost-effective systems. These sensors can supply essential data for a variety of applications, such as temperature, humidity, and pressure measurements, at a lower cost than their industrial counterparts. Conversely, the RS-485 standard offers reliable long-distance communication robust enough for industrial environments, where I²C solutions are impractical due to their limited range and susceptibility to interference. By integrating these two technologies using the proposed module, low-cost I²C sensors can be interfaced with industrial systems. This enables data acquisition from sensors over greater distances, thus expanding the potential applications of I²C sensors to domains where their use would typically be unfeasible. Unlike single-purpose solutions, the proposed system is characterized by its ability to enhance basic sensors by relocating certain software mechanisms to hardware modules, thereby optimizing resource utilization and improving communication security [10]. The key innovation is the combination of low cost and high durability, which overcomes the limitations (short range, low interference resistance) of inexpensive sensors by integrating them into a robust communication environment. Additionally, the proposed solution is designed to facilitate the connection of various types of sensors that communicate via the I²C protocol, thereby significantly expanding the range of potential applications. The work is not just a theoretical concept, but describes in detail a complete and real-world-proven hardware design, including multi-level protection circuits. It confirms the reliability and readiness of the solution for practical deployment in areas such as industrial automation, traffic monitoring, and smart buildings.

2. Materials and Methods

The primary objective of this study is to create a versatile and adaptable sensor communication module capable of both autonomous operation and seamless integration into distributed measurement networks, with a particular emphasis on its applicability in transport infrastructure monitoring. This paper is focused exclusively on the hardware implementation. The development of the corresponding firmware and a general-purpose software application for processing and visualizing the transmitted data will be detailed in a subsequent publication.

The existing body of literature indicates many solutions in the domain of sensor systems aimed at monitoring environmental parameters within transport infrastructure, which have been the subject of extensive research and technological advancements [11]. The available literature suggests a growing trend towards integrating low-power sensor networks, particularly those leveraging the IoT technologies, enabling efficient real-time monitoring of key physical parameters [12]. Existing research examines the design and optimization of autonomous, distributed sensor nodes often powered by renewable energy sources like photovoltaic panels. These nodes exhibit low power consumption, easy deployment, and wireless data transmission capabilities [13]. Concurrently, emphasis is placed on robustness and resilience to adverse environmental factors such as extreme temperatures, humidity, and electromagnetic interference (EMI) [14,15,16]. The literature frequently compares the characteristics of various communication protocols, including I²C, SPI, UART, and RS485 [17,18]. Due to its straightforward implementation and low power demands, the I²C protocol appears suitable for compact, short-range isolated systems. Conversely, the RS485 protocol is often preferred for demanding industrial applications requiring reliable data transmission over longer distances and in high EMI environments. A comparative analysis of the I²C and RS485 protocols is provided in

Table 1. I²C and RS485 buses comparison.

Parameter	I2C	RS485
Communication type	Serial, synchronous, two-wire	Serial, asynchronous, differential (two wires)
Transfer rate	100 kHz (standard), up to 5 MHz (ultra-fast mode)	Up to 10 Mbit/s (short bus)
Maximum distance	∼1 m	Up to 1200 m (at 100 kbps)
Number of devices on the bus	Up to 127 devices (at 7-bit address)	Up to 32 (without repeater), more with repeaters
Network topology	Star or bus	Bus (multipoint)
Addressing	Yes, 7- or 10-bit addresses	Not native—depends on higher layer protocol (e.g., Modbus)
Interference immunity	Low (sensitivity to electromagnetic interference)	High (differential transmission reduces the impact of interference)
Shared wires	Yes (SDA and SCL)	No—separate bus, not dependent on shared clock signal
Cabling intensity	Low—only 2 wires to communicate	Higher—requires separate communication link
Power consumption with more devices	Higher—continuous monitoring of shared bus	Lower—devices can be addressed selectively
Address management and conflicts	Potential conflicts—each sensor must have a unique address	Address management depends on higher layer protocol (e.g., Modbus)
Robustness in case of device failure	Low—failure of one device can affect others	High—failure of one node does not affect the rest of the network
Suitability for islanded systems (e.g., IoT)	High—low power, simplicity	Limited—higher energy and communication interface requirements
Possibility to integrate with other protocols	Limited	High—often used with Modbus, BACnet, DMX, and others

. The proposed design for the module includes primary functional blocks that ensure the core operation of the system, as well as auxiliary circuits that complement and support its functionality. These sections are clearly illustrated in Figure 1, which provides a comprehensive overview of the structure and the interconnections among the individual components. The blocks within the diagram are numbered and are further detailed in the subsequent text in numerical order, to ensure a clearer interpretation. Each block represents a specific functional unit, and its operation is briefly characterized, including its interfaces with other parts of the system. This block-based decomposition enables a precise understanding of the design logic, facilitating the subsequent implementation and testing of the entire module. In creating this design, authors used components and a PCB layout based on existing practical experience from solving similar tasks that were focused on monitoring environmental parameters in industrial applications and for research purposes. These previous designs and solutions have been the subject of publications [19,20] as well as an utility model [21].

2.1. Power Unit

The emphasis was placed on minimizing the internal power consumption of the supply circuit, as well as on its mechanical robustness and functional reliability across a wide range of operating temperatures. The overall solution thus reflects the needs of modern embedded systems, which have more demanding requirements for energy efficiency in diverse application environments [22]. The input of the power supply circuit was designed with a focus on multi-level protection and reliable operation under various conditions. The key protective element is a PTC (Positive Temperature Coefficient) resettable fuse, type SN02030. In conjunction with the input filter and an overvoltage protection circuit, it safeguards the electronics against overcurrent conditions, overvoltage, and improper power supply connection, including reverse polarity. Upon removal of the fault condition and subsequent cooling, the fuse automatically returns to its initial conductive state, thereby restoring circuit operation without the need for manual intervention. The input filter is implemented using the NFM21C series component, which functions as a capacitive element with low-pass characteristics. This filter effectively suppresses high-frequency interference originating from the input power line, thereby ensuring greater stability and reliability for the entire system [23]. When designing the input voltage range, two alternatives were considered: a nominal range with a maximum input voltage of 12 V and an extended range up to 24 V. Depending on the selected input level, the design specifies a different component configuration that accounts for regulation efficiency and the thermal stress on individual elements.

To accommodate the anticipated higher input supply voltage, the design incorporates a voltage regulator (type MCP1703) to produce a 5 V output. It is followed by another regulator of the same type in series, which provides the 3.3 V supply required by the microcontroller and the communication module. This dual-stage regulation facilitates the powering of circuits with different logic levels while minimizing unnecessary energy loss. The power supply branch also includes a resistive voltage divider, positioned after the input filter, which enables the microcontroller to monitor the supply voltage level. This feature allows for the detection of a low-voltage condition that could negatively impact the functionality of connected peripherals, particularly sensors.

2.2. RS-485 to Serial Circuitry

The communication solution is designed for use in industrial applications that require robustness against interference, multi-point connectivity, and the capability for reliable communication over extended distances. The module’s communication subsystem utilizes an RS-485 bus interface. The primary active component is the SN65HVD10D integrated circuit, which serves as a transceiver, converting signals between the differential RS-485 bus and the microcontroller’s serial TTL interface. This chip is designed for operation with a 3.3 V power supply and is optimized for low power consumption and high reliability in harsh industrial environments.

The design implements Transient Voltage Suppression (TVS) protection to protect the communication interface from damage caused by transient voltage events. When a voltage surge exceeds a predefined threshold, the TVS diode enters a conductive state, shunting the excess energy away from sensitive circuitry. This effectively protects the device from events such as electrostatic discharge (ESD), switching transients, and lightning-induced surges. Once the voltage returns to below the clamping threshold, the diode automatically reverts to its high-impedance (non-conductive) state, ready to protect against subsequent transient events [24].

The circuit also incorporates control logic for managing data direction, as the RS-485 standard operates in a half-duplex mode. The microcontroller controls the direction of transmission by sending a dedicated control signal to switch the transceiver between transmit and receive modes. The signal voltage levels between the communication IC and the microcontroller are properly matched to ensure reliable, error-free data exchange.

2.3. Microcontroller

The proposed design of the communication module utilizes a microcontroller from STMicroelectronics’ mainstream product line—specifically, the STM32F0x1, which is based on the ARM Cortex-M0 architecture. This microcontroller is implemented in a TSSOP-20 package, suitable for surface-mount technology (SMT), providing an effective solution for space-constrained applications. The configuration of peripheral and support circuitry has been designed following the recommendations provided in the manufacturer’s technical documentation. For system clock generation, the internal calibrated RC oscillator is sufficient for this application, ensuring adequate timing accuracy and stability without the need for an external crystal. In applications requiring minimized energy consumption, the original STM32F0x1 microcontroller can be replaced by the low-power variant, STM32L0x1, which is available in the same package and features an identical pinout. This pin-compatibility allows for straightforward design adaptation without requiring modifications to the printed circuit board layout.

The physical connection of peripheral circuits is designed with consideration for the specific component layout on the PCB and utilizes the alternate pin remapping functionality supported by the STM32F0x1 architecture. The microcontroller directly drives one signaling light-emitting diode (LED), while a second LED is controlled by the same pin that manages the data transmission direction on the RS485 communication line. For the microcontroller’s analog power supply rails, manufacturer-recommended decoupling capacitors and filtering circuits have been incorporated into the design. Expansion buses and the programming interface have been separated into connector headers on the PCB, ensuring straightforward configuration, debugging, and firmware updates during both development and subsequent operational deployment.

2.4. LED Status Lights

The circuit design incorporates a signaling section consisting of three high-intensity LEDs to provide visual feedback on the module’s operational status. The selection of high-efficiency LEDs allows the desired level of visibility to be achieved with lower current consumption, thereby contributing to the overall reduction in the device’s power requirements. Each LED is dedicated to indicating a specific system status:

• White LED indicates the presence of the supply voltage.
• Blue LED signals activity on the communication line.
• Orange LED is used to indicate fault conditions or specific operational states of the microcontroller, such as a firmware update (flashing) in progress.

Such a configuration enables basic on-site diagnostics of the device’s status without the need for external tools.

2.5. I²C Interface

To facilitate the connection of external sensors to the communication module, the PCB design incorporates support for the I²C bus. This standard two-wire serial interface enables communication with multiple peripherals. For the physical connection of sensors, two types of connectors have been implemented:

• A dedicated JST 2.0 connector, featuring compact dimensions, which is particularly suitable for permanent or production-level integrations.
• A standard 2.54 mm pitch pin header, which allows for flexible and rapid testing or swapping of sensors during development and debugging.

This dual-connector configuration ensures compatibility with a wide range of sensor modules, thereby enhancing the system’s overall versatility.

2.6. Sensor

During the development and testing of the functional prototype, the SHT30 sensor was used as a representative sensor. This device is a combined digital sensor designed for measuring both temperature and relative air humidity. The sensor communicates via the I²C interface and is characterized by its high accuracy, low power consumption, and compact mechanical form factor. Given its characteristics in

Table 2. SHT30 sensor [25] characteristics.

Parameter	Value
Supply Voltage	2.15 V to 5.5 V
Temperature Measurement Range	−40 °C to +125 °C
Relative Humidity Measurement Range	0% to 100% RH V
Measurement Accuracy	±2% RH over the 20% to 80% RH range ±0.2 °C over the 0 °C to 90 °C range
Measurement Resolution	0.01% RH, 0.01 °C
Communication Interface	I2C, including support for CRC (Cyclic Redundancy Check) to ensure data transmission integrity
I2C Address Options	0x44 or 0x45 (selectable)

, the SHT30 sensor is well-suited for deployment in applications where the continuous monitoring of environmental conditions is required, such as in transportation infrastructure, storage facilities, or in systems for intelligent metering and microclimate control.

The SHT30 sensor is mounted on a dedicated PCB. To ensure power supply quality and suppress high-frequency interference, a 100 nF decoupling capacitor is implemented on the sensor’s PCB. The I²C bus communication lines are equipped with 10 k$\Omega$ pull-up resistors, which ensure that the data (SDA) and clock (SCL) signals return to a logic HIGH level when not being actively driven low. To ensure the sensor’s resilience against adverse weather conditions and to prevent moisture condensation on the PCB surface, the entire sensor board is coated with a protective dielectric film, thus reducing the likelihood of short circuits and providing protection against corrosion. Subsequently, the PCB is encapsulated in a protective polyethylene (PE) housing, as shown in Figure 2.

The electrical interconnection between the sensor module and the main communication PCB is established using a four-pin HY2.0-4P connector, which provides the connections for power, ground, and the I²C communication lines. The temperature measurement accuracy and relative humidity measurement tolerance of the Sensirion SHT30 sensor [25] are quantified in the performance graphs shown in Figure 3a,b. These graphs offer a detailed overview of measurement deviations as a function of temperature and humidity conditions, with the declared values being consistent with the manufacturer’s technical datasheet.

3. Results

Based on the aforementioned design of the communication module’s functional blocks, detailed circuit schematics have been developed for the individual sections of the device, reflecting the established requirements for functionality, reliability, and immunity to external disturbances.

Figure 4 presents the electrical schematic of the module’s power supply circuit, which integrates protective elements and stabilization components. The build variants for two distinct input voltage ranges (up to 12 V and up to 24 V) are summarized in

Table 3. Summary of different components for two supply voltage ranges.

Part	5.5–12 VDC	7.5–24 VDC
CF1	NFM21PC104	NFM21PC222
F1	SN020-30	SN020-30
D1	PESD15VS1UB	PESD24VS1UB
IC1	MCP1703-5002	UA78M05DCY

. The design accounts for the need for high operational reliability with minimized internal power consumption, as well as the ability to withstand transient fluctuations in the supply voltage. The proposed power supply section has a maximum current consumption of 100 µA.

Figure 5 illustrates the circuit design for the microcontroller and its support circuitry, including decoupling capacitors, filtering for the analog power supply, communication interfaces, and the programming and expansion headers. The design follows the manufacturer’s recommendations for the STM32F0x1 microcontroller [26] and allows for substitution with the more energy-efficient STM32L0x1 variant without requiring any modifications to the PCB layout.

The resulting design of the functional prototype of the communication module, with all components populated, is shown in Figure 6a,b.

Field testing of the universal I²C/RS485 module prototype, equipped with the SHT30 combined I²C temperature and relative humidity sensor (depicted in Figure 7a,b), was conducted from 14–27 February 2025. The tests took place on the campus of the University of Žilina, specifically near a high-traffic roadway (Figure 8). The module was installed in a distribution cabinet, where it was connected to a 12 V power supply. For data communication, the module was linked to an RS232/485 to Ethernet converter.

Data logging and transmission occurred at regular ten-minute intervals. The resulting plots of the measured temperature and relative air humidity values are visualized in Figure 9a,b. These field tests confirmed the proper functionality and high reliability of the designed universal communication module, thereby demonstrating its suitability for deployment in real-world environmental monitoring applications. The proposed solution was successfully tested over a 650 m cable length, exhibiting no communication errors during operation.

4. Discussion

This paper presents the design and implementation of a universal sensor module that connects the local I²C bus to the RS-485 industrial interface. The results of this work should be interpreted in the context of the growing need for robust and flexible sensor networks in the Industrial Internet of Things (IIoT) and the monitoring of critical infrastructure. The key working hypothesis was that the strategic integration of these two interfaces could lead to the creation of a modular and scalable solution that overcomes the limitations of existing systems, where it is often necessary to choose between ease of sensor integration and reliability of long-distance communication.

The successful implementation and verification of the module’s functionality confirm this hypothesis. While many previous studies focus either on the development of application-specific sensors or on communication protocols for IIoT, the presented solution acts as a universal hardware bridge. It enables the seamless integration of a vast number of commercially available and low-cost I²C sensors, originally designed for consumer electronics or prototyping, into industrial networks that require high interference immunity and long-range capabilities, which RS-485 provides. It addresses the common issue of developing expensive, custom sensor units for industrial deployment.

The implications of this solution extend beyond the field of transport infrastructure. In the broader context of industrial automation, smart agriculture, or environmental monitoring, this module can significantly reduce the cost and complexity of building distributed measurement systems. It enables rapid prototyping and subsequent deployment of systems that can monitor a wide range of physical quantities (temperature, humidity, pressure, air quality) using a single, standardized hardware platform. The emphasis on robustness, demonstrated by the implementation of multi-level protection circuits, further confirms the module’s readiness for deployment in real, demanding conditions, which distinguishes it from typical development kits.

When comparing the proposed module with commercially available solutions in

Table 4. Comparison with available solutions.

Solution	Type/Usage	Interfaces	Adaptability	Key Features	Limitations
Proposed solution	Universal module	I2C, RS-485	Very high (open firmware on STM32, open hardware)	Full control over firmware, hardware protections, optimization for specific applications, low component costs.	Requires development and testing, lacks industrial certification.
M5Stack COMMU [27]	Commercial module	I2C, CAN, RS-485, TTL	Low (module designed for the M5Stack ecosystem)	Simple integration, small size, multiple interfaces in one.	Limited customization options, more suited for prototyping than industrial deployment.
Coptonix RS485 I2C Adapter [28]	Industrial converter	I2C, RS-485	Medium (configuration via ASCII commands)	Industrial standard, I2C level shifter, adjustable address via DIP switches.	Higher price, limited firmware flexibility, focused only on conversion.
TI TIDA-01281 [29]	Reference design	Isolated I2C, CAN, RS-485	High (reference design for further development)	Fully isolated interfaces, complies with industry standards (IEC), robust solution for demanding environments.	Requires implementation and production, and has a higher design complexity.

, several key differences emerge, highlighting its specific benefits (such as full control over firmware) and added value. For example, platforms such as M5Stack COMMU [27] offer RS-485 connectivity within a system, making them ideal for rapid prototyping. However, according to available data, such solutions lack multi-level electrical protection (e.g., against ESD and voltage transients) and increased resistance to environmental influences, which were central design goals of our module, making them less suitable for reliable and long-term deployment in demanding industrial conditions. Closer to the basic functionality is the Coptonix RS485 I²C adapter (Coptonix GmbH, Berlin, Germany) [28], which also serves as a dedicated bridge. The main difference in our work lies in its open design and emphasis on verifiable robustness, offering a customizable and potentially more cost-effective concept compared to a proprietary, commercially available unit. Finally, at a much higher level of complexity, reference designs such as Texas Instruments’ TIDA-01281 (Texas Instruments, Dallas, TX, USA) [29] represent complex industrial gateways with features like redundant Ethernet. Our module is not intended to compete with such systems, but rather to serve as a complementary, low-cost edge device. It provides a key first link in the data chain—connecting individual sensors to the network in a simple and scalable manner, which could then feed data into a larger gateway.

Although basic functionality has been demonstrated, further research should take several directions. The primary goal is to implement and validate a standardized communication protocol, such as Modbus RTU, directly on the module’s microcontroller. It would ensure immediate software interoperability with existing SCADA systems and industrial control units (PLCs). Furthermore, extensive testing under real operating conditions is necessary to quantify long-term reliability and resistance to environmental influences. Another interesting direction is to explore low-power variants using microcontrollers from the STM32L family, which, in combination with energy harvesting technologies, could lead to the creation of autonomous, maintenance-free sensor nodes for long-term monitoring tasks.

5. Conclusions

This work aimed to design, construct, and verify the functionality of a universal sensor module suitable for industrial applications. The presented solution successfully fulfilled the set objectives through a modular and robust hardware design. The main result is a functional module that integrates a local I²C bus for the flexible connection of a wide range of sensors with an RS-485 industrial communication bus, ensuring reliable data transmission over long distances and in environments with strong EMI. The design emphasizes high reliability, which is achieved through the robust construction of the power supply and communication circuits, incorporating integrated protective elements.

Verification of the prototype’s functionality with the SHT30 digital temperature and humidity sensor confirmed the viability and correctness of the proposed concept. The proposed sensor module is a practical and adaptable building block for creating distributed measurement and monitoring systems. Its properties make it ideal for use in areas such as intelligent transport, industrial automation, and Internet of Things (IoT) systems, where high demands are placed on reliability, modularity, and low operating costs. This work demonstrates that the proposed communication module enables the reliable integration of low-cost I²C sensors into robust industrial systems, a development that promises substantial economic impact via reduced capital and operational expenditures. The module’s universal architecture provides for the flexible monitoring of various environmental parameters, accommodating all available I²C sensor types to meet specific user demands. Crucially, the module eliminates the inherent constraints that have historically restricted I²C sensor solutions from widespread industrial application.