ESP32 PLC on the plant floor: when Wi-Fi, LoRa or 4G is the right link

An ESP32 PLC is the right controller when the job needs a network more than it needs a big CPU: machines that must send data, remote sites without cable, or equipment a phone should control.

The real design question is the link. Ethernet, Wi-Fi, Bluetooth LE, LoRa and 4G each fit a different place on the plant floor.

What is an ESP32 PLC?

An ESP32 PLC is a programmable logic controller built around the ESP32 chip from Espressif, packaged for industrial use: DIN rail mounting, a 12 to 24 Vdc supply and industrial inputs and outputs.

The Industrial Shields ESP32 PLC family has 8 models, from 9 inputs and 5 outputs (ESP32 PLC 14) to 37 inputs and 24 outputs (ESP32 PLC 58). You program all of them with the Arduino IDE, over USB or Ethernet.

Ethernet first, wireless where there is no cable

Every ESP32 PLC model has an Ethernet port. When a cable reaches the cabinet, use it: Modbus TCP to a SCADA, MQTT to a broker or HTTP to an API, with no radio planning.

Wireless is for the places a cable does not reach, or should not reach:

RS-485 is on every model too, for Modbus RTU with meters, drives and sensors inside the cabinet.

Wi-Fi for machines that cannot get a cable

Wi-Fi helps most in retrofits. An old machine has no data, and the cabinet sits far from the nearest switch.

In the machine monitoring projects, an ESP32 PLC reads run, stop, cycle and reject signals, counts parts and sends each event over MQTT. If the network fails, the data waits on the SD card and goes out when the link is back. See the packaging line retrofit and the MQTT with SD buffer recipe.

LoRa and 4G for remote sites without staff

Pumping stations and tanks are far away, have no staff and often no fixed network. A failure shows up only when the water stops.

Each station runs on its own ESP32 PLC: a level probe on 4-20 mA, pump alternation and failover. Alarms and data go over LoRaWAN or 4G to one control room.

LoRa covers long distances with low power and little data. 4G sends more data, straight to the cloud, where there is mobile coverage. Real installations: water network telecontrol and FEDA water consumption monitoring.

Bluetooth LE when a phone is the panel

Mobile hydraulic equipment has no fixed panel and no network. An ESP32 PLC 38R talks to a phone app over Bluetooth LE and runs the valves with a state machine.

One rule we keep: overpressure protection stays in the PLC, never in the app. The phone sends requests. The PLC decides.

The link will drop: design for it

Every wireless link drops sometimes. Decide what the PLC does before it happens:

• Buffer the data. Keep events on the SD card and send them when the link is back.
• Keep a known state. A watchdog moves each output to its default state when the controller stops hearing the server.
• Keep the logic local. Interlocks and protections run in the PLC. The network only carries data and commands.

The gate control project shows this pattern: an ESP32 PLC 42 reads commands from a MySQL table, moves pneumatic gates and keeps a known state when the network drops. Read how it works.

Choose the ESP32 PLC model by I/O count

Pick the model by the number of inputs and outputs, not by the link. Every model has Ethernet, Wi-Fi, Bluetooth LE and RS-485, and every model accepts the optional LoRa or 4G board. RS-232 is on every model except the ESP32 PLC 14.

Data from each product page. Check the datasheet before you wire the controller. When the project grows, add I2C expansion modules or a second PLC. Compare all 8 models.

Try it before you choose

• Run the closest simulator in your browser: machine monitor, remote site telemetry or gate control.
• Start from tested code in the PLC Solution Library.
• See the seven ESP32 PLC projects and send us your signal list.