Case study · Railway · ESP32 PLC 57R
Comfort on board. Energy data that waits for coverage.
Light, ventilation and A/C on board. Energy data over 4G LTE-M.
The carriage stays comfortable. The PLC keeps the numbers.
When coverage drops, the data waits on board.
This case describes a railway operator that wanted to control and monitor its train carriages. It does not name the operator, the line or the trains. The original installation used an M-Duino 54ARA with an integrated GPRS module. This page shows the same system built today with an ESP32 PLC 57R and a 4G LTE-M (LTE Cat M1) board: what one controller does inside a carriage, not where the train is.
The challenge
Safe, efficient and comfortable carriages. And the energy in numbers.
The customer manages a railway network. Its main goal was a control and monitoring system for the train carriages of the company, for the safety, efficiency and comfort of passengers and staff on board. The case lists six parameters: lighting, ventilation, air conditioning, temperature, humidity and energy.
Light where it is needed
Ambient light in a carriage changes all the time. The lighting must follow the real light level, not a fixed schedule.
Climate in range
The values inside the carriage must stay within the established ranges. If they leave them, ventilation and air conditioning must react.
Energy you can measure
The operator wants to see the energy consumption of each wagon, find ways to reduce it, and plan maintenance with data.
A link that comes and goes
The data travels over a mobile network to a control unit. When coverage is lost, the data must not be lost with it.
Six parameters, one controller
Lighting, ventilation, air conditioning, temperature, humidity and energy on one ESP32 PLC 57R with a 4G LTE-M communication board.
How it works
Three loops: light, climate, energy.
Each loop shows one part of the system. Move the sliders and press the buttons. The panels are illustrative simulations: light levels, temperatures, ranges, limits and record times are examples, not data from the installation.
A light sensor tells the PLC when to switch the lighting.
A light sensor measures the ambient light level in the carriage. The PLC opens or closes the light circuit, so the lighting follows what the carriage needs. The case also says the lighting can be dimmed as required, without more detail. A typical way to do it: two light levels, one to close the circuit and one to open it, so the lights do not flicker at the limit. Move the light level in the panel.
- Light sensor inside the carriage, connected to the PLC
- The PLC opens or closes the light circuit
- Example: on below 150 lx, off above 300 lx
Illustrative simulation. Example values, no data from the installation. Example rule: the PLC closes the light circuit below 150 lx and opens it above 300 lx. The gap avoids switching on and off at the limit.
Out of range, the PLC starts ventilation or air conditioning.
A temperature and humidity sensor monitors the values inside the carriage all the time. When the values go outside the established ranges, the PLC activates the ventilation and/or the air conditioning. The case also lists an alert to maintenance staff after a dangerous temperature rise. A typical way to do it: high humidity starts the ventilation, high temperature starts the air conditioning, and a higher limit sends an alert. Move the sliders.
- One sensor for temperature and humidity
- Ventilation and/or air conditioning when a value leaves its range
- Alert to maintenance staff after a dangerous temperature rise
PLC decisions (example)
Illustrative simulation. Example values, no data from the installation. Example ranges: 20 to 26 °C and 30 to 60 % humidity. Alert to maintenance above 35 °C. The real ranges are not published.
Energy data goes out over 4G LTE-M. Without coverage, it waits on board.
A voltage sensor connected to the PLC measures the energy consumption of the wagon. The PLC sends the data to a control unit over the mobile network: 4G LTE-M on the ESP32 PLC 57R, GPRS in the original installation. If coverage is lost, the PLC keeps the data on board until the connection is restored, and then sends it automatically. In the original installation, the buffer was the SD card of the controller. Press Lose coverage, wait, then restore it.
- Voltage sensor on the wagon supply, connected to the PLC
- Energy data to a control unit over 4G LTE-M
- Local buffer during loss of coverage, automatic sending after
Energy records (example)
Illustrative simulation. Example values, no data from the installation. Example: one energy record per minute, time sped up. The case does not publish the record period or the data format.
Code example: ESP32 PLC datalogging with a buffer when the network is down
System architecture
How does an ESP32 PLC with 4G LTE-M control and monitor a train carriage?
Three sensors connect to the ESP32 PLC 57R: light, temperature and humidity, and voltage. The PLC drives the light circuit, the ventilation and the air conditioning of the carriage. It sends the energy data to a control unit over 4G LTE-M, and keeps it in a local buffer while there is no coverage.
| Signal | Between | Type | Purpose |
|---|---|---|---|
| Ambient light | BetweenLight sensor → ESP32 PLC 57R | TypeInput | PurposeLight level in the carriage. Signal type not published |
| Temperature and humidity | BetweenT/H sensor → ESP32 PLC 57R | TypeInput | PurposeValues inside the carriage, compared with the established ranges |
| Voltage | BetweenVoltage sensor → ESP32 PLC 57R | TypeInput | PurposeEnergy consumption of the wagon |
| Light circuit | BetweenESP32 PLC 57R → lighting | TypeOutput | PurposeOpens or closes the light circuit |
| Ventilation and A/C | BetweenESP32 PLC 57R → ventilation, air conditioning | TypeOutput | PurposeStart when temperature or humidity leave their ranges |
| Energy data | BetweenESP32 PLC 57R → control unit | Type4G LTE-M | PurposeConsumption data of the wagon. Protocol not published. GPRS in the original installation |
| Data buffer | BetweenESP32 PLC 57R → local storage | TypeOn board | PurposeKeeps the data during loss of coverage. Sent automatically when the link is back. SD card in the original installation |
| Maintenance alert | BetweenESP32 PLC 57R → maintenance staff | TypeNot published | PurposeDangerous temperature rise or a lighting problem |
Why it works
One controller on board. Data that arrives late, not never.
4G LTE-M on the PLC
The ESP32 PLC 57R takes a 4G (M1)-NB1 IoT LTE communication board. No separate modem in the carriage. The original installation chose a controller with an integrated GPRS module for the same reason.
Store and forward
Without coverage, the data stays on board. When the link is back, the PLC sends it automatically. The control unit gets the data later, instead of losing it.
Decisions on board
Light and climate rules run in the PLC, next to the sensors and the loads. The mobile link carries data. It does not switch the lights.
Mixed I/O on one unit
18 inputs and 33 outputs on the ESP32 PLC 57R. One possible split: the 12 analog inputs for the sensors, the 24 relays for the loads, the 9 analog outputs if a load needs a reference.
Data for maintenance
Continuous values from every carriage help to find faults in lighting, ventilation and air conditioning, and to plan the work before a failure.
Open and modular
Programmed with the Arduino IDE, with no licence fees. The ESP32 PLC grows with up to 127 expansion modules over I2C.
Hardware
ESP32 PLC 57R with a 4G LTE-M board.
ESP32 PLC 57R with the 4G (M1)-NB1 IoT LTE board
An ESP32 based industrial PLC for DIN rail, with analog inputs for the sensors, relays for the loads and an optional 4G LTE Cat M1 communication board for the data link to the control unit.
- Role
- Light and climate control, energy data over 4G LTE-M
- Inputs
- 18: 12 analog/digital (0-10 V, 11-bit), 6 digital optoisolated
- Outputs
- 33: 24 relays, 9 analog/digital/PWM (0-10 V)
- Mobile link
- Communication board 4G (M1)-NB1 IoT LTE (u-blox SARA-R412M), option
- Other comms
- Ethernet, Wi-Fi, Bluetooth LE, RS-485, RS-232, I2C, SPI
- Built in
- Real-time clock
- Power
- 12 to 24 Vdc, DIN rail
The original installation used an M-Duino 54ARA with an integrated GPRS module (26 inputs, 25 outputs), no longer in the web shop. On the product page, choose the 4G (M1)-NB1 IoT LTE board as communication board 1.
Questions about this case
How does an ESP32 PLC control lighting, ventilation and air conditioning in a train carriage?
With sensors and simple rules on board. A light sensor tells the PLC when to open or close the light circuit, and a temperature and humidity sensor tells it when to start the ventilation and/or the air conditioning: when the values leave the established ranges. On the ESP32 PLC 57R, the sensors go to the 0-10 V analog inputs and the loads to the relays. The ranges of the installation are not published. The panels on this page use example values.
What happens to the data when the train loses mobile coverage?
The PLC keeps it on board until the connection is restored, and then sends it automatically. This is store and forward. In the original installation, the buffer was the SD card of the controller. A typical way to build it: add a timestamp from the real-time clock to each record, write it to local storage, send the oldest records first when the link returns, and delete or mark each record only after the control unit confirms it. See the ESP32 PLC datalogging example with a buffer and our SD card basics for an industrial PLC.
Can a voltage sensor alone measure energy consumption?
The case names a voltage sensor that measures the energy consumption of the wagons. Energy is power over time, and power is voltage times current (and power factor in AC). So the voltage needs a current measurement, or a fixed known load, to give energy. A common choice is an energy meter with a pulse output or Modbus RTU on RS-485, which the ESP32 PLC can read. The case does not publish the rest of the measuring chain.
Why 4G LTE-M instead of GPRS for a new railway project?
GPRS runs on 2G networks, and some mobile operators have switched off 2G or plan to do it. Before a new project, check coverage and end dates on your routes, in every country the trains cross. LTE Cat M1 (LTE-M) is made for IoT devices and supports handover between cells, so it suits a moving train. The ESP32 PLC 57R takes a 4G (M1)-NB1 IoT LTE board (u-blox SARA-R412M). The store and forward logic stays the same.
Which standards apply to electronics on board a train?
In Europe, electronic equipment on rolling stock usually follows EN 50155 (environment, power supply, tests) and EN 50121-3-2 (electromagnetic compatibility). Fire safety follows EN 45545-2. The case does not say how the installation was certified. Ask your operator for the requirements before you design. Our engineers can review them with you.
Which parts of this case are facts, and which are examples?
Facts of the original case: a railway network operator, a control and monitoring system for train carriages, an M-Duino 54ARA with an integrated GPRS module, a light sensor that makes the PLC open or close the light circuit, a temperature and humidity sensor that starts ventilation and/or air conditioning out of range, a voltage sensor for energy consumption, data sent to a control unit, and an SD card buffer during loss of coverage with automatic sending after. Current option on this page: the ESP32 PLC 57R with a 4G LTE-M board. Examples: light levels, temperature and humidity ranges, the alert limit, record times and the data format.
Download the case study
4-page PDF with the challenge, the logic, the architecture and the hardware. No form required.
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