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UniPi Neuron M503


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


  • universal architecture with increased number of analog I/Os
  • compact size, durable aluminium chassis (IP20 protection)
  • integrated Raspberry Pi Model 3B 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

439,00 € - 515,48 €
362,81 € - 426,02 € excl. TAX
More than 20 items in stock



The M503 is the smallest model of the 500 lines (consisting of the M503, L503 and L513 models) and like the rest of the 500 lines, it features multiple analogues I/O modules and additional RS485 universal bus port while retaining a set of digital and relay I/O capability. The M503 represents a smaller variant of the L503 unit.  

Inputs & Outputs

10 digital inputs (DI) are designed for reading logical states (true or false), which are represented by levels of DC voltage. That makes them suitable for reading two-state sensors such as switches (on/off), movement sensors (movement/no movement), water level sensors (water present, no water) etc. The software detects logical 1 (true) if the input voltage between given DIx.y and DIGND is between 5-30V. If the voltage is lower than 3.5V, the state is evaluated as 0 (false)

4 digital outputs (DO) are used for controlling two-state devices such as lights, door locks, window blinds etc. Digital outputs on our controllers also feature the PWM (Pulse-width modulation) function, enabling a special type of analogue control. Outputs are of the NPN type (open collector) and can control devices with voltage up to 50V and up to 750mA load current.

5 relay outputs are used for control or switching of devices with higher current loads. ROs are thus suitable for controlling light bulbs, thermoelectric valve drives, water heaters, pumps etc. Relay outputs on UniPi controllers are rated for 5A max. current at 230V AC/30V DC voltage.

5 analogue inputs (AI) The controller features two types of analogue inputs. Group 1 analogue input (AI1.1) can be used either for voltage (0-10V) or current (0-20mA) measurements depending on AI register settings. Group 2 analogue inputs (AI/AIS2.1-AI/AIS2.4) feature four modes based on register settings. 

  • voltage measurement 0-10 V (16bit resolution)
  • voltage measurement 0-2.5 V (24bit resolution)
  • current measurement 0-20 mA (16bit resolution)
  • resistance measurement (from PT100, PT1000 or NTC sensors) using three-wire (three conductors, 0-100 Ω, 24bit resolution) or two-wire (two conductors, 0-1960 Ω, 24bit resolution) wiring method.

5 analogue outputs (AO) The controller features two types of analogue outputs. Group 1 output (AO1.1) can be used for 0-10V DC voltage, 0-20mA direct current or for resistance measurements (0-2kΩ, Ni1000 or Pt1000). Group 2 analogue outputs (AOV2.1-AOV2.4) feature 0-10V DC voltage only. 

Detailed info about I/O usage and settings can be found in Neuron technical documentation (see the Files tab above)

Communication interfaces

The controller features a pair of RS485 serial lines for communication with external devices or connection of extension modules, most often through the Modbus RTU protocol. Serial lines can be used for communication with a wide variety of devices such as energy meters, touchscreen HMI panels, PLCs from other vendors or Neuron xS series extension modules) using the Modbus RTU protocol. A single RS485 can communicate with a high number of devices with its total length being up to several hundred meters. Lines can be also used as an RS485 gateway for other devices or systems.

Included is also a single 10/100MBit Ethernet port for network communication and a single 1-Wire bus for connection of various 1-Wire sensors (such as digital thermometers). The 1-Wire bus uses 2 or 3 conductors for communication with simple sensors such as thermometers, humidity meters or light intensity meters. A single bus can communicate with up to 15 sensors with a maximum total length of the bus up to 100 meters.

Software options

Customers can choose from a wide variety of software solutions thanks to the open nature of Neuron controllers and are not limited to a single platform. Available are both professional and open-source solutions.

Our main supported solution for UniPi controllers is the MervisThis platform is developed under IEC 61131-3 PLC programming standard and contaiíns SCADA interface for remote management and monitoring, comprehensible development environment, user interface (HMI) editor and online/on-premise database for data archivation and retrospective operation analysis of monitored technologies. 

Neuron controllers are also compatible with the CODESYS professional platform. designed specifically for use in modern industrial automation. At the same time, the platform is made to be as user-friendly and easy to use as possible. CODESYS is in widespread use around the globe with more than 100 000 users from various countries and more than 1000 companies.

Aside from commercial platforms, several open-source solutions are available as well. Alternatively, customers can use their code or implement Neurons into already existing software solutions through the use of EVOK open-source API.

Visit this link for supported software overview. 

Other features

All UniPi controllers can measure resistance through analogue I/Os. Resistance can be measured by either the 2-wire or 3-wire method for increased accuracy. Each controller can measure the resistance of up to 2kΩ, with some models being able to resistance measure up to 100kΩ. Detailed info about this functionality can be found in Neuron technical documentation. 

All components are encased within a durable anodized aluminium case providing IP20 cover. The unit's size is 8 DIN modules, DIN rail holder is included in the package. 

Package contents

  • controller
  • pluggable screw terminals
  • DIN rail holder (35 mm)
  • DIN rail holder screws
  • microSD card (optional)
  • +24V DC power supply (optional
  • Mervis lifetime license

Possible uses

  • Lightning control
  • Boiler control
  • Temperature measurement
  • Remote home control
  • Remote shutter control
  • Notification sending
  • Energy monitoring
  • Gateway for other systems
  • Irrigation systems
  • Building management systems
  • HVAC control and regulation
  • SCADA systems


Neuron is CE and EMC tested and is compliant with all corresponding European PLC standards. By these standards Neuron can be used in: 

  • Residential buildings, apartments
  • Commercial areas, offices, banks
  • Entertainment areas, cinemas, bars, pubs, dance clubs
  • Outdoor places, gas stations, parking lots, sport centres
  • Areas of light industry, workshops, laboratories, service centres

The EU declaration of conformity can be found in the Files tab (see above). 

Standard Neuron model overview

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

Quad-core CPU, 1 GB RAM
1-Wire bus (up to 15 sensors per channel)
10/100Mbit Ethernet
Wi-Fi, Bluetooth, HDMI
4× USB 2.0

S103 4 4 - 1 1 1
S103-G* 4 4 - 1 1 1
S103-IQRF** 4 4 - 1 1 1
Type 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
M403 4 4 28 1 1 1
M503 10 4 5 5 5 2
Type 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
L503 24 4 19 5 5 2
L513 16 4 10 9 9 3

Extension modules (size on DIN rail: 4 modules = 7 cm)

xS10 16 - 8 - - 1

Extension modules communicate over Modbus. It is possible to connect them to the control unit via a RS485 interface. Extension modules are compatible with any control unit with the RS485 interface and Modbus support.

xS30 24 - - - - 1
xS40 8 - 14 - - 1
xS50 6 - 5 4 4 1

* features an integrated wireless GPRS module.
** features an integrated TR-76D smart IQRF transceiver

Further info


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

CPU 4 × 1 GHz
USB 2.0 4
Ethernet 10/100 BaseT
Transistor outputs 4
Analog inputs 5
Digital inputs 10
Analog outputs 5
RS485 interface 2 ×
Power 24 V DC
Relay outputs 5
1-Wire bus Yes (galvanically isolated)
Dimensions 140 mm × 90 mm × 60 mm
Weigth 750 g
Mounting DIN (35 mm)
RTC backup maximum 7 days
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