How to choose an Arduino PLC: seven checks and five options

Start here: a board with shields, or a finished controller

Many projects start as an Arduino board with an optocoupler board, a relay board and a terminal breakout. That works on the bench. For a machine that ships, every one of those parts needs wiring, a DIN-rail mount and a parts list someone has to rebuild and check for each unit.

An Arduino PLC puts field inputs, relay or transistor outputs, screw terminals and an industrial power input on one DIN-rail board, and the maker supplies the board package for the Arduino IDE. If the machine will be built more than once, or handed to a maintenance team, a finished controller is usually the shorter path.

Seven checks for choosing an Arduino PLC

1. Count your I/O, then add margin. List every sensor, switch, valve, contactor and lamp. Decide whether you want one controller that already has that many points, or a small base unit plus expansion modules. A board with the full count is simpler to wire and to stock; expansion modules let you change the mix later.

2. Check the input type. Most industrial proximity and photo sensors are NPN or PNP. Check whether the inputs accept both, whether they are opto-isolated, and what voltage counts as ON. Analog inputs differ more: some read 0–10 V only, some read 4–20 mA directly, some take NTC thermistors, and some change range by jumper or by order option.

3. Check the output type and rating. Relays switch AC or DC loads. Transistor outputs switch DC loads faster and without contact wear. Look at the rating per point and per common terminal, because the common decides which loads have to share a supply.

4. Decide on the network. If the controller itself must sit on Ethernet, run Modbus TCP or report to a cloud dashboard, you need an Ethernet port. If it talks to an HMI or other devices over RS-485 with Modbus RTU, a serial port is enough and the wiring is simpler.

5. Decide how you will program and upload it. All of these run Arduino sketches. Beyond that, check for ladder logic and the other IEC 61131-3 languages, and whether ladder and C can live in the same project, so a technician who reads ladder and a developer who writes C can work on one machine. Check how the program gets onto the board: some controllers upload over a plain USB cable, others need a specific programming cable. Check which operating system the tool runs on.

6. Check certification early. If your customer, panel shop or inspector requires UL, cULus, ETL or CE, apply that filter before you compare anything else. It removes options faster than any other check, and the answer can differ between models of the same family.

7. Check how you will buy and get help. Distributor stock in your country, lead time, payment method, how much tutorial and forum material exists, and who answers technical questions all matter once the machine is in the field.

Recommendations by situation

The controller must be on Ethernet or Wi-Fi. Arduino Opta, CONTROLLINO MAXI or MEGA, or an M-Duino. ILOGICS boards have no Ethernet port; the separately sold M-ETHER converter adds Modbus TCP through a serial port.

You need a UL, cULus or ETL certified controller. Arduino Opta (cULus), CONTROLLINO MINI, MAXI or MEGA (UL Certificate of Compliance; check for the UL Mark on the unit), or an M-Duino 21, 42 or 58 (ETL). ILOGICS has no UL listing.

Your team writes structured text or FBD. Arduino Opta with Arduino PLC IDE.

You want ladder for the sequence and C for the math, in one project. MPINO or MPAINO with MPINO STUDIO2. The ladder runs inside your loop() and shares memory with your code, so a technician can follow the rungs while the scaling and protocol code stay in C. The Arduino PLC page shows how a project is laid out.

You have NPN or PNP sensors and want every digital input isolated. MPINO or MPAINO. The digital inputs counted in the model name (8 on an MPINO-8A8R-S, 64 on an MPAINO-64A64R) are all opto-isolated, and NPN or PNP is set by how you wire the common terminal.

You read 4–20 mA transmitters or NTC thermistors. MPINO -S models, such as the MPINO-8A8R-S with 4 analog inputs that read 4–20 mA as shipped and 2 NTC inputs. For M-Duino, the 19R and 21 product pages say to add a shunt resistor to their 0–10 V inputs for a current loop. For 0–10 V transmitters, ILOGICS changes analog inputs to 0–10 V when you order an MPINO-8A8R-S, MPINO-8A8T-S, MPINO-8A4R-SU, MPINO-16A16R or MPINO-16A8R8T.

You need many points on one controller. The MPAINO-64A64R has 64 inputs and 64 relays on one ATmega2560. CONTROLLINO MEGA reaches 21 inputs, 24 digital outputs and 16 relays. Opta grows through expansion modules.

Your HMI talks Modbus RTU over RS-485. Any option with RS-485 works if you write the communication code. MPINO STUDIO2 also has a built-in Modbus RTU slave, so an HMI can read and write ladder memory without communication code. See connecting an HMI.

Each comparison page lists what was checked and where: Arduino Opta alternative, CONTROLLINO alternative and M-Duino alternative.

When a conventional PLC is the better tool

Choose a conventional PLC from an established automation brand when:

• the function is safety-related,

• the end customer specifies a brand,

• your maintenance staff and spare parts are built around one vendor, or

• the machine needs hot-swappable rack I/O.

Before using any controller on this page for a safety function, check the maker's safety rating. ILOGICS controllers carry none. For the wider trade-offs, read industrial Arduino vs traditional PLC.