Open Source IPC. Powered by the Raspberry Pi Compute Module, the base modules are the core of every Revolution Pi modular system.

The RevPi Core is with 22.5mm only half as wide as the RevPi Connect, but has twice as many PiBridge connectors, namely two. This means that the RevPi Core can be upgraded with up to 10 expansion modules. Like the RevPi Connect series, the RevPi Core series is also equipped with the Raspberry Pi Compute Module 4S or Compute Module 3+, depending on the variant. A Real Time Clock (RTC) with 24 h buffering ensures that the device always knows what time it is, even in the event of a power failure. As with all Revolution Pi base modules, a specially adapted version of Raspbian with real-time function is used as the operating system.

For those who can do without features such as a second Ethernet interface or an RS-485 connection in their projects, the RevPi Core is an attractively priced alternative to the RevPi Connect without having to compromise on the expansion modules.

The RevPi Core comes in the following variants:

• RevPi Core S - powered by Compute Module 4S
• RevPi Core SE - powered by Compute Module 4S
• RevPi Core 3+ - powered by Compute Module 3+

Generally, the only difference between the RevPi Core variants mentioned above are the built-in Raspberry Pi compute modules. The exception here is the RevPi Core SE variant, which does not support the gateway expansion modules.

Full power

The power supply circuit is one of the most important parts of the RevPi Core. In order to get as small heat from power dissipation as possible it uses state-of- the-art high-efficiency DC-DC-converter (efficiency over all is greater than 80 %). These converters use 24 VDC input (which is the usual case in industrial applications) to produce all supply voltages needed for the Core.

But the Core module does not only run on the standardized supply range of 20.4 V to 28.8 V but also runs on as little as 10.2 V input voltage*. That means you can even use car batteries or solar panels as power supply. At 24 V input any power loss of up to 10 ms will not influence operation of RevPi Core (drawing full current from both USB ports) and even up to 25 ms without USB load. Input voltage and functional earth is connected to RevPi Core using heavy duty connectors at the bottom side.

A sophisticated protection circuit guarantees continuous operation even under massive electrical or electro-magnetic interference on the input power lines (provided that functional earth is connected properly). Lightning strikes and nearby welding machines have been simulated in test laboratories but could not impress the RevPi Core modules.

In addition, the Revolution Pi has a Real Time Clock with 24 h buffering, which ensures that the device always knows what time it is, even in the event of a power failure.

* RevPi Core can only drive 2 x 500 mA USB 5 V supply using input voltages greater than 11 V. EN 61131 demands a minimum of 10 ms tolerance against power failure which can only be guaranteed with input voltages form 20.4 V to 28.8 V. At 12 V input voltage this time decreases drastically, especially when driving loads by USB ports.

Interfaces

Like Raspberry Pi, RevPi Core is equipped with common interfaces.

• Ethernet plug - Connect RevPi Core to a LAN by using the RJ45 Ethernet connector.
• USB plug - The RevPi Core is equipped with two USB-A connectors at the front side which can be used for USB 2.0 client devices. Both connectors can drive up to 500 mA at their 5 V supply pins. Therefore you may plug USB drives or surf sticks directly into these connectors without the need for an active USB hub.
• Micro USB plug - You can connect an USB Host system (usually a PC) with the RevPi Core using the Micro-USB connector in the middle of the front plate. The RevPi Core will then boot in passive eMMC access mode and behave like an USB client memory stick. That way you may flash the module for the first time using an image file from a PC.
• Micro HDMI plug - One Micro-HDMI plug, e.g. for connecting a video monitor.

Highly modular

The data highway connecting all RevPi modules is called PiBridge. The modules are physically connected to each other, using a system connector on the top side. Three signal types are exchanged via this connector:

4 pins of the PiBridge are used for automatic module detection during start up phase. After this phase RevPi Core exactly knows which modules are connected and in which physical position they are.

4 pins of the PiBridge are used for rapid data exchange of small data packages using RS485 signals. This channel is also used for module configuration during start up phase. After configuration this channel is used for cyclically exchanging data between RevPi Core and all IO modules connected.

8 pins of the PiBridge are used for rapid data exchange of large amount of data using Ethernet signals. Up to now this channel is only used by our modular gateway modules which may collect up to 512 Byte data cyclically from nearly all relevant fieldbusses.

Tough

One of the major goals was to make Raspberry Pi ready for tough industrial environment, so it could become a real IPC which meets the EN 61131-2 standard.

• Power supply: 12-24 VDC -15 % / +20 %, max. 10 W
• Operating temperature: -25 °C to 55 °C
• ESD protection: 4 kV/8 kV according to EN 61131-2 and IEC 61000-6-2
• Surge / Burst tests: applied according to EN 61131-2 and IEC 61000-6-2
• EMI tests: according to EN 61131-2 and IEC 61000-6-2
• UL certified (UL-File-No. E494534)

Open Source Software

Despite the fact that Revolution Pi is an open system on which everyone can install their own apps and software, Kunbus have tried to equip Revolution Pi with software and apps that cover most applications.

The operating system used is a customized version of Raspbian, which includes a real-time patch of the kernel. This is in Kunbus' view the best compromise to stay as close as possible to the original development environment of a Raspberry Pi and still get a high level of control over the priorities of the tasks managed by the scheduler. The scheduler, which controls the execution of tasks by the operating system, can be extensively configured with this modified kernel, so that delays usually caused by network and other I/O accesses are avoided. Suitable drivers for the expansion modules are of course already pre-installed.

Azure certified device

Collecting sensor data, processing it and sending the processed data to a cloud is one of the Revolution Pi’s strengths. Therefore, the RevPi Core has been certified by Microsoft Azure. The certification ensures that the integration with one of the most important cloud platforms can be done as smoothly and easily as possible.

Node-RED

The pre-installed open source software Node-RED is an excellent tool for the realisation of simple automation tasks and rapid prototyping. With the specially developed RevPi Nodes the Revolution Pi modules are seamlessly integrated into Node-RED.

Modbus capabilities

Revolution Pi comes with master and slave capability for the popular Modbus RTU and Modbus TCP network protocols. External gateways are therefore in most cases no longer necessary when using these two network protocols.

Modbus TCP works with the Ethernet interface available on the RevPi Core (i. e. via the RJ45 socket on the front panel) or any other Ethernet connection (e. g. USB WLAN adapter) that is supported by the TCP/IP protocol.

Modbus RTU requires a TTY device under Linux. Since the existing UART interface of the compute module is already reserved for the PiBridge and therefore not available, a USB to serial converter such as an RS485 converter is required (not included in scope of delivery).

The configuration is done via the browser-based, graphical configuration software PiCtory.

Specifications

Interfaces

• 1 x RJ45 Ethernet sockets
• 2 x USB 2.0 sockets
• 1 x Micro HDMI socket
• 1 x Micro USB 2.0 socket
• 2 x PiBridge (for RevPi Con expansion modules)

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