Arduino Opta Pinout and I/O Guide: Inputs, Relays, RS485, Ethernet and Expansion

The Arduino Opta is a compact industrial micro PLC designed around the same high-performance STM32H747 family used by several Portenta boards.

Unlike a normal Arduino board, its external connections are designed around industrial terminal wiring:

The key to understanding Opta is that its I/O is not exposed as ordinary 3.3 V or 5 V GPIO headers. The front screw terminals include signal conditioning, relay contacts and industrial interfaces.

Opta Variants

The Opta family is currently available in three main versions:

Variant	Ethernet	USB-C	RS-485	Wi-Fi / BLE
Opta Lite	Yes	Yes	No	No
Opta RS485	Yes	Yes	Yes	No
Opta WiFi	Yes	Yes	Yes	Yes

The core PLC I/O is otherwise similar across the family.

Main Processor

Opta is built around the:

with:

This dual-core architecture allows high-level communications and control logic to be separated from time-critical tasks.

Memory

The Opta platform includes the STM32H747 internal memory plus:

for application storage and firmware-related functions.

Power Supply Terminals

The first four top terminals are used for power:

Opta accepts:

which makes it suitable for standard industrial control cabinets.

The two positive and two negative terminals simplify daisy-chaining and distribution inside a panel.

Power Consumption

Arduino currently specifies approximately:

for the Opta itself.

This does not include power consumed by external relay loads.

Eight Programmable Input Terminals

The Opta input terminals are:

These can be used as:

Arduino Pin Mapping

Opta terminal	Arduino pin	STM32H747 pin
I1	A0	PA0_C
I2	A1	PC2_C
I3	A2	PF12
I4	A3	PB0
I5	A4	PF10
I6	A5	PF8
I7	A6	PF6
I8	A7	PF4

Input Voltage Range

The digital inputs accept:

while analogue acquisition is intended for:

signals.

Do not assume that because the digital input can accept 24 V, the analogue measurement range is also 24 V.

Digital Input Thresholds

Arduino’s current Opta datasheet specifies approximately:

for digital-input interpretation.

This leaves a deliberate transition region between the two logic states.

Digital Input Current

Arduino specifies approximately:

for the input circuitry.

Input Frequency

The current datasheet specifies a digital-input frequency capability of approximately:

This is useful for:

• pulse counters;
• flow-meter outputs;
• slow encoders;
• proximity sensors;
• machine-cycle counting.

Analogue Acquisition Cycle

Arduino lists an analogue input acquisition cycle around:

under the documented conditions.

Inputs Can Generate Interrupts

All eight programmable inputs support Arduino-style interrupt handling.

For example:

I1 and I4 Interrupt Limitation

There is an important hardware limitation:

cannot both be used simultaneously as interrupt sources.

Other combinations are supported, which means up to seven of the eight inputs can be used simultaneously for interrupts.

Four Relay Outputs

Opta contains four physical electromechanical relays:

All four contacts are:

Arduino Relay Mapping

Relay	Arduino pin	STM32H747 pin
Relay 1	D0	PI6
Relay 2	D1	PI5
Relay 3	D2	PI7
Relay 4	D3	PI4

Relay Current Rating

Arduino specifies:

with:

under the documented relay conditions.

Relay Voltage Ratings

The current datasheet lists:

with a resistive AC1 load rating around:

DC Relay Capacity Depends Strongly on Voltage

The DC1 breaking-capacity figures drop sharply as DC voltage increases.

Arduino lists approximately:

This is an important reminder that a relay’s:

cannot be applied blindly to every DC voltage.

No Built-In Short-Circuit Protection on Relay Contacts

Arduino’s current datasheet explicitly states:

so external fusing should be used where required.

Relay Response Time

The electromechanical relays are much slower than transistor outputs.

Arduino specifies roughly:

plus contact bounce.

They are therefore appropriate for:

• contactors;
• lights;
• heaters;
• valves;
• slow actuators;

but not high-frequency PWM.

Relay Example

Always remember that the software pin controls the relay coil; the external load is connected through the isolated relay contact terminals.

Status LEDs

Opta provides four programmable front status LEDs:

mapped to:

These can be used independently from the relay-contact electrical path.

User Button

The front programmable user button maps to:

and can also be used as an interrupt source.

Reset Button

A separate hardware reset button is provided for restarting the controller.

Ethernet on Every Opta Variant

All current Opta versions include:

with an onboard:

and Ethernet status LEDs.

This makes Ethernet available even on the entry-level Opta Lite.

USB-C

All Opta variants include:

which can be used for:

• programming;
• USB peripheral mode;
• USB host mode;
• data logging to USB storage;
• firmware/program updates.

USB Power Limitation

USB-C can power the processor for programming and development, but Arduino notes that USB power does not power the PLC relay/load side in the same way as the 12-24 V industrial supply.

For normal PLC operation, use the proper DC input terminals.

RS-485 on Opta RS485 and Opta WiFi

The RS-485-capable variants expose:

for half-duplex differential serial communication.

This is suitable for:

• Modbus RTU;
• custom RS-485 protocols;
• industrial sensors;
• drives;
• meters;
• remote I/O.

No Onboard RS-485 Termination

Arduino explicitly states:

on Opta’s RS-485 interface.

If Opta is at one physical end of a Modbus/RS-485 trunk, add the termination required by the bus design.

A/B Naming Can Vary Between Vendors

RS-485 naming conventions are unfortunately inconsistent.

Opta labels the terminals:

If communication fails with another manufacturer’s equipment, verify that vendor’s A/B polarity convention before troubleshooting software.

Opta WiFi Adds Wireless Connectivity

The Opta WiFi variant adds:

plus:

using the onboard wireless module.

Wi-Fi Operating Modes

The wireless interface can operate as:

• station;
• access point;
• simultaneous AP + station.

Arduino documents Wi-Fi throughput up to approximately:

under supported conditions.

Secure Element

Opta includes a:

secure element.

This provides hardware support for:

• device identity;
• private-key storage;
• certificate-based authentication;
• cloud credentials;
• secure provisioning.

Real-Time Clock

The STM32H747 includes a hardware RTC with:

• calendar;
• sub-second timing;
• alarms;
• timestamp support;
• leap-year handling.

This is useful for industrial:

• event logs;
• alarms;
• scheduled control;
• maintenance records;
• production timestamps.

Expansion Connector

Opta includes a side expansion port intended for:

This allows the base PLC to grow without replacing the controller.

Digital Expansion Modules

Arduino currently offers digital expansion modules such as:

Each adds:

Up to Five Expansion Modules

Arduino currently documents support for:

which can be mixed depending on application requirements.

Analogue Expansion

The current Opta analogue expansion family adds industrial analogue functionality including:

• voltage inputs;
• current inputs;
• resistive/temperature measurement;
• analogue voltage outputs;
• analogue current outputs;
• PWM outputs.

Opta as a Small PLC System

A practical installation can therefore grow from:

into a much larger controller using side-mounted expansion modules.

Arduino IDE Programming

Opta can be programmed as an Arduino board using conventional C/C++ sketches.

The current Arduino core exposes familiar functions such as:

with the industrial I/O mapped to Arduino-style pin names.

PLC IDE Programming

Opta also supports the Arduino PLC IDE and IEC 61131-3 languages including:

• Ladder Diagram;
• Structured Text;
• Function Block Diagram;
• Sequential Function Chart;
• Instruction List in the Arduino PLC environment.

Arduino IDE vs PLC IDE Memory Configuration

Opta can be configured differently depending on whether it is used with:

Arduino provides a memory-partitioning procedure when moving an Opta from PLC IDE use back to the normal Arduino environment.

Dual-Core Programming

The STM32H747 allows the:

cores to communicate through an RPC mechanism.

A typical advanced design could use:

Common Mistake 1: Treating I1-I8 as Ordinary GPIO

These are industrial input terminals with conditioning circuitry.

Do not bypass the terminal design and assume they behave like bare 3.3 V pins.

Common Mistake 2: Applying 24 V in Analogue Mode

The digital inputs can handle 24 V signalling, but the specified analogue measurement range is:

Do not use the full digital-input voltage range as an analogue measurement range.

Common Mistake 3: Treating Relay Ratings as Universal

A 10 A AC relay rating does not mean:

Always check the actual load type and DC breaking-capacity table.

Common Mistake 4: Forgetting External Relay Fuses

The relay contacts do not provide short-circuit protection.

Use correctly rated external protection where required.

Common Mistake 5: Adding PWM to the Relay Outputs

These are mechanical relays with millisecond response times and finite electrical life.

They are not PWM outputs.

Common Mistake 6: Assuming RS-485 Termination Is Built In

Opta has no onboard RS-485 termination resistor.

Add termination externally where the bus topology requires it.

Common Mistake 7: Expecting RS-485 on Opta Lite

The Lite model includes:

but not the RS-485 terminal hardware.

Common Mistake 8: Assuming Wi-Fi Is on Every Opta

Wireless is only present on:

not Opta Lite or Opta RS485.

Quick Terminal Reference

Final Thoughts

Arduino Opta is best understood as:

The most important pinout detail is that the eight input terminals are not just digital inputs:

The four outputs are also genuine normally-open relay contacts rather than MCU GPIO.

For small industrial and building-automation projects, Opta provides a much more installation-ready architecture than a bare development board.

For larger I/O systems, the side expansion port allows the same controller to grow with digital and analogue modules.

For a more I/O-heavy industrial controller using the same STM32H747 family, see our Arduino Portenta Machine Control pinout guide. For CAN fundamentals on the STM32H747 family, see our Arduino GIGA R1 CAN bus guide.