R4DIF08: 8-Channel Digital Input Module with RS485 and Modbus RTU

R4DIF08 is a compact 8-channel digital input acquisition module designed to collect digital signals and transmit their status to a host controller through an RS485 serial interface. Supporting Modbus RTU communication, it provides a practical solution for PLC expansion, industrial monitoring, smart home automation, and distributed control systems.

By converting eight digital input signals into Modbus-readable data, the R4DIF08 helps engineers integrate switches, sensors, and other digital signal sources into centralized monitoring systems without requiring a dedicated input interface for every device.

According to Eletechsup's published product specifications, the module supports a 6–24 V DC supply, TTL-compatible 5 V and 3.3 V input signals, configurable input polarity, and both polling and automatic reporting modes.

2. Key Features

  • 8 digital input channels: Monitor up to eight independent digital signals.

  • RS485 communication: Suitable for distributed installations and multi-device serial networks.

  • Modbus RTU protocol: Supports function codes 03 and 06 for reading input status and configuring supported parameters.

  • Flexible input logic: Supports low-level triggering by default, with an alternative high-level input mode.

  • TTL and LVTTL compatibility: Designed for 5 V TTL and 3.3 V LVTTL signal interfaces.

  • Configurable serial communication: Default baud rate of 9600 bps, with additional supported rates of 1200, 2400, 4800, and 19200 bps.

  • Multiple-device networking: The manufacturer specifies support for up to 247 devices in Modbus command mode, subject to network addressing and electrical installation requirements.

  • Compact design: Approximately 44 × 29 × 15 mm, with a listed weight of around 10 g.

3. Technical Specifications

Parameter Specification
Model R4DIF08
Digital inputs 8 channels
Operating supply DC 6–24 V
Typical nominal supply DC 12 V
Working current Approximately 8–12 mA
Input logic Low-level default; high-level mode available
Input signal compatibility TTL 5 V / LVTTL 3.3 V
Communication interface RS485
Communication protocol Modbus RTU
Default baud rate 9600 bps
Other supported baud rates 1200, 2400, 4800, 19200 bps
Input status Query mode and automatic reporting
Dimensions Approximately 44 × 29 × 15 mm
Weight Approximately 10 g

Specifications are based on the published product listing. Confirm the applicable hardware revision and manual before finalizing an installation.

4. How the R4DIF08 Works

The R4DIF08 reads the electrical states of its eight digital input channels and makes the resulting status available through RS485 communication.

A typical installation consists of digital signal sources, the R4DIF08 input module, an RS485-to-USB adapter or host controller, and software that reads Modbus RTU data.

For example, an automation system may use the module to monitor:

  • Eight limit switches on a machine.

  • Door and window contact sensors.

  • Eight equipment-running or fault signals.

  • Digital status outputs from other electronic controllers.

  • Multiple discrete signals in a remote monitoring cabinet.

The host can periodically query the module for the current input states. Where supported and configured, automatic reporting can reduce the need for continuous polling.

5. GitHub Integration: Python and Modbus RTU

The GitHub project ul-gh/cheap_modbus_rtu provides a practical software example involving the Eletechsup R4DIF08.

The project documents an R4DIF08 Python class that can be used to read all eight digital inputs. This is useful for engineers who want to integrate the module into a Linux-based automation system or a Python monitoring application.

Example usage from the project's documentation:

from cheap_modbus_rtu import R4DIF08

# The documented default slave ID is 1
input_module = R4DIF08(
    slave_id=1,
    serial_device_name="/dev/ttyUSB0"
)

inputs = input_module.get_inputs()
print(inputs)

In this example:

  1. The Python library imports the R4DIF08 interface.

  2. The host connects through a serial device, such as an RS485-to-USB adapter.

  3. The software queries the module for its digital input states.

  4. The returned data can be printed, logged, or passed to other application logic.

The serial device name and slave address must match the actual installation. The required Python package, serial permissions, and adapter configuration should also be checked before running the example.

GitHub reference: https://github.com/ul-gh/cheap_modbus_rtu

6. Applications and Market Demand

Industrial Automation

The R4DIF08 can collect machine status signals, limit-switch states, and fault indicators for a PLC or supervisory monitoring system. Its small size is useful when a project requires additional digital inputs without a large I/O expansion rack.

Smart Home and Building Automation

It can interface with compatible contact sensors and digital status outputs for centralized monitoring of doors, windows, equipment, and other discrete signals.

Remote Monitoring Systems

RS485 is widely used in distributed control environments. With suitable wiring and Modbus-compatible host software, multiple modules can be integrated into a shared monitoring network.

Embedded Systems and Custom Software

The documented GitHub Python interface provides a starting point for custom dashboards, data logging, test equipment, and small automation applications. Developers can use the collected input states as part of a larger monitoring workflow.

7. Why Choose Eletechsup R4DIF08?

The R4DIF08 combines eight digital inputs, RS485 communication, and Modbus RTU in a compact, cost-conscious module. It is particularly suitable for projects that need to acquire several digital signals and make them available to a PLC, PC, or embedded controller.

Its documented use in a public GitHub software project also gives developers a practical starting point for Python integration, rather than requiring every application to be built entirely from scratch.

For engineers evaluating the module, the key considerations are input voltage compatibility, trigger logic, communication settings, wiring, and hardware revision.

Conclusion

The Eletechsup R4DIF08 is an economical option for eight-channel digital signal acquisition in industrial automation, building monitoring, and embedded control applications. Its Modbus RTU interface supports integration with compatible controllers, while the GitHub Python example demonstrates one practical approach to reading input states from software.

Product information: Eletechsup R4DIF08

GitHub software example: cheap_modbus_rtu

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