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Unipi Neuron L503


UniPi Neuron L503 is a programmable logic controller (PLC) designed for control, monitoring and regulation. The L503 represents an intermediate model of the Neuron 500 line, focused on an increased number of analog I/O. The L503 also features an additional RS485 serial line and is an enlarged variant of the M503 model.

Note: This product was phased out of production and was replaced by the Neuron L523.


  • universal architecture with a very high number of I/Os
  • increased number of analog I/Os, additional RS485 line
  • durable aluminium chassis (IP20 protection)
  • integrated Raspberry Pi 3 Model B computer (quad-core CPU, 1 GB RAM)
  • designed for DIN rail mounting
  • features RS485 serial line for Modbus communication
  • software openness (based on Linux OS)
  • Mervis lifetime license as part of the package

SD card
Power Supply

529,00 € - 605,48 €
437,19 € - 500,40 € excl. VAT
out of stock


Basic description

The L503 is an intermediate model of the Neuron 500 line (consisting of the L503, M503 and L513 models) and like the rest of the 500 lines, it features multiple analogue I/Os and additional RS485 universal bus port while retaining a set of digital and relay I/O capability. Multiple analogue inputs can be used for automation tasks requiring either receiving of voltage or current signal for gathering data from corresponding sensors (such as resistance thermometers), while analogue outputs are designed for control and regulation of external devices such as three-way valves or heat exchangers.

Basic features

Digital inputs 24 Common features
Raspberry Pi 3 Model B computer
(1,2GHz quad-core CPU, 1GB RAM)
4× USB 2.0
1× 10/100Mbit Ethernet
Wi-Fi, Bluetooth, HDMI port
Aluminium chassis (IP20)
Digital outputs 4
Relay outputs 19
Analogue inputs* 5
Analogue outputs* 5
RS485 serial interface 2
1-Wire bus 1

*more detailed info about the number and type of analogue I/Os is available in the product's datasheet (see the Files tab above)

Inputs & outputs description

Digital inputs (DI) are designed to read binary logic states represented by direct voltage levels. That makes them suitable for reading data from various binary sensors and devices such as switches (on/off), motion sensors (movement detected/not detected), liquid level sensors (full tank/empty tank) etc. 

Digital outputs (DI) are intended for switching various binary devices (lighting, smart door locks, drives of shutters and blinds etc.) through direct voltage. DO's also feature a Pulse-Width Modulation (PWM) function allowing to use the output for analogue control. 

Relay outputs (RO) are primarily used for switching two-state devices with higher current draw such as lightbulbs, thermoelectric valve drives, water heaters, pumps etc.

Analogue inputs (AI) are designed to measure voltage, current or resistance to read values from various analogue sensors such as thermometers, pressure meters, tensometers etc.

Analogue outputs (AO) serve for control of multi-state external devices through direct voltage or current and is suitable for control and regulation of devices such as three-way valves, heat exchangers, electric motors etc. 

Computing module

As a computing module, the Neuron controllers use the Raspberry Pi 3 Model B featuring quad-core 1.2GHz CPU and 1GB RAM. That gives them more than enough performance for various performance-demanding applications. MicroSD memory cards are used as memory storage. 

Communication interfaces

Neuron controllers are by default provided with RS485 serial lines. This type of interface usually uses the Modbus RTU protocol and can be used to communicate with various devices such as Extension xS extension modules, energy meters, touchscreen HMI displays, controllers from other vendors, various sensors etc. A single bus can support dozens of devices while the bus' length can reach up to several hundred meters.

A single 1-Wire bus is also included. This interface uses 2-3 conductors for collecting data from various 1-Wire sensors such as thermometers, humidity meters, light intensity sensors etc.). A single 1-Wire bus supports up to 15 devices, the overall length of the bus can reach up to 100 meters. 

All Neuron models also feature a single 10/100Mbit Ethernet port for network communication

Software options

Thanks to the software openness of Unipi controllers customers can choose from a broad range of software solutions and are not limited to a single proprietary platform. Among supported solutions are both commercial and open-source systems. 

The main supported platform for Unipi controllers is the Mervis control system. This platform is developed under the IEC 61131-3 PLC programming standard and consists of comprehensible and user-friendly Mervis IDE development environment, an HMI editor for creating and editing of user interfaces, SCADA interface and an online/on-premise cloud database for long-term collecting of operational data and their analysis. 

Aside from commercial platforms (such as CODESYS), customers can also choose from a variety of open-source solutions; for the supported software overview please visit this link.

Alternatively, customers can use the Unipi-developed EVOK open-source API to integrate Unipi controllers into already existing software solutions, use custom code or to develop applications for the controllers.

Package contents

  • Neuron controller
  • removable screw terminals
  • DIN rail holder (35 mm)
  • 2× DIN rail holder mounting screws
  • 1× grounding screw
  • instruction leaflet
  • lifetime Mervis license code

Other features

All components of the controller are encased within a durable aluminium chassis (IP20 protection). The controller is designed for mounting on a standard DIN rail (35 mm). 

Neuron product line overview

Name DI DO RO AI AO RS485 Common features
Type S, size on DIN rail: 4 modules = 7 cm

Raspberry Pi 3 Model B computer
(1,2GHz quad-core CPU, 1GB RAM)
4× USB 2.0
1× 10/100Mbit Ethernet
Wi-Fi, Bluetooth, HDMI port
Aluminium chassis (IP20)

S103 4 4 - 1 1 1
S103-G* 4 4 - 1 1 1
S103-IQRF** 4 4 - 1 1 1
Typ M, size on DIN rail: 8 modules = 14 cm
M103 12 4 8 1 1 1
M203 20 4 14 1 1 1
M303 34 4 - 1 1 1
M523 8 4 5 5 5 2
Typ L, size on DIN rail: 12 modules = 21 cm
L203 36 4 28 1 1 1
L303 64 4 - 1 1 1
L403 4 4 56 1 1 1
L523 24 4 19 5 5 2
L533 12 4 10 9 9 3

* GSM/GPRS module
** IQRF-compatible

Further information


Modbus register map
Table overview of Modbus registers
Declaration of conformity
User manual
User manual and technical documentation
Instruction leaflet
Technical and safety information
Product datasheet
Datasheet of the product

USB 2.0 4
Ethernet 10/100 BaseT
Digital inputs 24
Relay outputs 19
Transistor outputs 4
Analog inputs 5
Analog outputs 5
RS485 interface 2 ×
RTC backup maximum 7 days
1-Wire bus Yes (galvanically isolated)
CPU 4 × 1 GHz
Power 24 V DC
Mounting DIN (35 mm)
Dimensions 210 mm × 90 mm × 60 mm
Weigth 546 g

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