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UniPi Axon M515


UniPi Axon M515 is a programmable logic controller (PLC) designed for control, monitoring and regulation. The M515 is based on the M505 model, but with four digital I/Os being replaced by additional analog I/Os for the total of 8× AI + 8× AO.


  • focused on a high number of I/Os
  • highest number of analog I/Os, four serial lines (RS485 + RS232)
  • durable aluminium chassis (IP20 protection), wider operating temperature range
  • integrated industrial computer (quad-core CPU, 1 GB RAM)
  • onboard 8GB eMMC memory
  • designed for DIN rail mounting
  • RS485 and RS232 serial lines
  • software openness (based on Linux OS)
  • preinstalled Mervis software (can be manually reflashed)

Power supply

599,00 € - 627,09 €
495,04 € - 518,26 € excl. TAX
More than 20 items in stock



The UniPi Axon M515 features an increased number of analogue I/O's. In contrast to the M505 model, the M515 has digital outputs and four digital inputs replaced by three additional analogues I/O modules. The unit thus features 8 analogue I/O's. Relay outputs and a pair of RS485 were retained with the 1-Wire bus being replaced by an RS232 line.

Inputs & Outputs

6 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 5-35V. If the voltage is lower than 3.5V, the state is evaluated as 0 (false)

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.

8 analogue inputs (AI) can be used for 0-10V DC voltage or 0-20mA current measuring, making them suitable for reading values from analogue sensors such as temperature sensors, pressure meters, tensometers etc.  The M503 (as well as other Neuron 500 controllers) is provided with two types of analogue inputs. Group 1 analogue input (AI1.1) does not feature the option to read data from resistance sensors, it can be however used for voltage or current measurement based on AI register settings. Group 2 analogue inputs (AI2.1-AI2.4) then allow the user to perform precise measurements of voltage, current or resistance based on current output 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.

8 analogue outputs (AO) feature two modes - 0-10V DC voltage or 0-20mA direct current. AI serves for control of devices with analogue input, such as three-way valves, lighting dimmers etc. Group 2 analogue outputs of the M503 (AO2.1-2,4) feature 0-10V voltage only.

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

Communication interface

The unit features two RS485 serial lines. This type of serial line most often uses the Modbus RTU protocol. It can be used for communication with a wide variety of devices such as energy meters, touchscreen HMI panels, PLCs from other vendors or our Neuron xS extension modules. The bus can communicate with up to 32 devices with its total length being up to several hundred meters.  

The controller also features a single RS232 serial line for communication between two devices. In automation, it is most often used for communication with HMI displays, various gateways or closed technologies. 

For network communication, a single 1Gbit Ethernet is provided.

Software options

Customers can choose from a wide variety of software solutions thanks to the open nature of Axon 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 in accordance with 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 storage and retrospective operation analysis of monitored technologies.

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

Visit this link for supported software overview. 

Other features

8GB eMMC onboard memory provides a high degree of reliability during repeated rewrites compared to systems using memory cards.

All components are protected by a durable anodized aluminium case providing IP20 protection. The unit’s size is 8 DIN modules, DIN rail holder is included in the package. 

Standard model overview

Product DI DO RO AI AO RS485 RS232 1-Wire Common features
Type S, size on DIN rail: 4 modules (7 cm)  
S105 4 4 - 1 1 2 1 1

Common features

Ethernet 1 Gbit

4x 1.2 GHz, 1GB RAM


Wi-Fi, Bluetooth

S115 4 4 - 1 1 4 - 1
S155* 4 4 - 1 1 2 1 1
S205 8 - 8 - - 1 - 1
S215 8 - 8 - - 1 1 -
S505 - - - 4 4 1 - 1
S515 - - - 4 4 1 1 -
S605** - - - - - 1 1 -
Type M, size on DIN rail: 8 modules (14 cm)
M205 20 4 14 1 1 2 1 1
M505 10 4 5 5 5 3 1 1
M515 6 - 5 8 8 2 1 -
Type L, size on DIN rail: 14 modules (21 cm)
L205 36 4 28 1 1 2 1 1
L505 24 4 19 5 5 3 1 1

*2x Ethernet (1 Gbit + 10/100 Mbit)
**4x IEC 62386 (DALI-compatible)

Further info


Technological specification of the product

CPU 4x 1.2 GHz
Internal memory 8GB eMMC
USB 2.0 2
Ethernet 1 Gbit
Digital outputs 6
Analog inputs 8
Analog outputs 8
Dimensions 140 mm x 90 mm x 60 mm
Relay outputs 5
RS485 interface 2
RS232 interface 1
1-Wire bus Yes (galvanically isolated)
Weigth 750 g
Mounting DIN (35 mm)
Power 24V DC
RTC backup max. 7 days

UniPi Axon S515

399,00 €
329,75 € excl. TAX

Less than 20 items in stock Show variants