Simplify Industrial Control with Flexible Digital I/O Expansion

Looking for a flexible way to expand digital inputs and outputs in an automation system?

The Eletechsup 25IOA08, 25IOB16, and 25IOC32 series provides an RS485 Modbus RTU remote I/O solution with 8, 16, or 32 digital input channels and an equal number of PNP transistor output channels.

Designed for PLC expansion, equipment monitoring, building automation, and distributed control applications, this series combines optically isolated inputs, high-level PNP outputs, and configurable control modes in a compact module.

Product link: https://eletechsup.com/products/25ioa08-25iob16-25ioc32-8-32-di-do-pnp-to-pnp-rs485-modbus-rtu-remote-io-module-dc-12-24v-300ma-dmos-pnp

1. Three Channel Options for Different Projects

Different automation projects require different numbers of I/O points. The 25IO series offers three models to help users select the right capacity for their systems.

• 25IOA08: 8 digital inputs and 8 digital outputs

• 25IOB16: 16 digital inputs and 16 digital outputs

• 25IOC32: 32 digital inputs and 32 digital outputs

Whether you are building a small control system or managing a larger number of field signals, you can choose a suitable channel count without changing the basic product series.

This makes the range useful for machine control, sensor monitoring, distributed switching, and multi-point automation projects.

2. PNP High-Level Outputs for Modern Control Systems

One of the defining features of this series is its DMOS PNP high-level output design, with a rated maximum drive current of 300 mA per channel.

PNP outputs are useful in systems that require a sourcing output signal, making the series suitable for compatible PLC input circuits, control interfaces, and low-current electronic loads.

Unlike conventional mechanical relay modules, these outputs use semiconductor switching. This can be advantageous when applications require electronic switching without mechanical relay contacts.

Typical applications include:

• PLC digital input signal control

• Indicator lights and compatible LED control circuits

• Low-current electronic switching

• Automation interface circuits

• Compatible industrial control inputs

Important: These are transistor outputs, not mechanical power relays. Each output is limited to 300 mA, and the load voltage, wiring, and total power requirements must remain within the module's specifications.

3. Optically Isolated Digital Inputs

The series provides 8, 16, or 32 optically isolated digital input channels, depending on the model.

NPN or PNP input configurations are available, allowing users to select a suitable version for compatible sensors, switches, and control signals.

Optical isolation helps separate field input signals from the module's internal circuitry, improving electrical isolation between connected circuits.

This feature is useful in automation installations where multiple sensors and external control signals need to be collected through a centralized I/O interface.

4. Standard RS485 Modbus RTU Communication

The 25IO series communicates through RS485 using the Modbus RTU protocol, making it suitable for integration with compatible PLCs, industrial controllers, computers, and automation software.

Supported baud rates include 1,200, 2,400, 4,800, 9,600, 19,200, 38,400, 57,600, and 115,200 bps. The default baud rate is 9,600 bps.

The documented Modbus command modes support multiple function codes, including read and write operations. Users should select the appropriate command mode and function codes for their host software.

RS485 communication also makes it practical to connect remote I/O equipment over a serial bus rather than running every individual field signal back to a central controller.

5. Multiple Output Control Modes

The 25IO series supports several output control modes, including:

• Open/Close: Turn an output on or off.

• Toggle (Self-locking): Change and retain the output state.

• Latch (Interlocking): Use interlocking control behavior.

• Momentary (Non-locking): Activate an output temporarily.

• Delay: Apply a configurable delay to output operation.

The documented command mode supports delays of up to 255 seconds.

These functions make the modules adaptable to a variety of control requirements, such as timed switching, momentary activation, and coordinated output control.

The input ports can also be configured to control output ports on another compatible board over the RS485 bus, enabling distributed control applications when the supported command mode is used.

6. Expandable Multi-Module Systems

For projects requiring more I/O points, the documented Modbus command mode supports up to 64 devices in parallel.

This allows system designers to consider multiple modules for distributed installations rather than relying on a single large I/O board.

Potential applications include:

• Multi-zone building automation

• Distributed sensor and switch monitoring

• Industrial equipment control

• LED and indicator control systems

• Security and access-control interfaces

• Remote I/O expansion for compatible PLC systems

Actual system capacity depends on the selected command mode, device addressing, bus wiring, communication settings, and host-controller implementation.

7. Compact Design and Flexible Power Supply

The modules operate from a DC supply in the 7–25 V range, making them suitable for compatible 9 V, 12 V, and 24 V control systems.

Their approximate board-only dimensions are:

Model	I/O channels	Board dimensions
25IOA08	8 DI + 8 DO	61 × 72 × 18 mm
25IOB16	16 DI + 16 DO	106 × 72 × 18 mm
25IOC32	32 DI + 32 DO	196 × 72 × 18 mm

A DIN-rail enclosure option is also available for installations that require convenient mounting inside a control cabinet.

The different board sizes give users flexibility to balance installation space against the number of required I/O channels.

8. Why Choose the Eletechsup 25IO Series?

The 25IOA08, 25IOB16, and 25IOC32 provide a practical combination of digital input acquisition, PNP output control, and standard RS485 Modbus RTU communication.

Key advantages include:

• Three channel-count options: 8, 16, or 32 inputs and outputs

• Optically isolated digital inputs

• Optional NPN or PNP input configurations

• PNP high-level transistor outputs rated up to 300 mA per channel

• Multiple output control modes

• Configurable serial communication speeds

• Support for multi-module RS485 systems

• Optional DIN-rail mounting enclosure

For engineers, system integrators, and automation developers, this series offers a straightforward way to expand digital I/O while keeping field signal acquisition and output control in a compact remote module.

Choose Your Model

Eletechsup 25IOA08, 25IOB16, and 25IOC32 are suitable for projects that need PNP output control and RS485-based digital I/O expansion.

Choose the 8-channel model for smaller systems, the 16-channel model for medium-sized installations, or the 32-channel model when more I/O points are required.

Visit the official product page to compare available versions and select the configuration that matches your application.

Official product page: https://eletechsup.com/products/25ioa08-25iob16-25ioc32-8-32-di-do-pnp-to-pnp-rs485-modbus-rtu-remote-io-module-dc-12-24v-300ma-dmos-pnp

Before ordering, confirm the input configuration, output wiring, current requirements, and Modbus command mode against the product documentation.