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Member

Registered: 2015-10-30

Posts: 45

Rex Control System on Raspberry Pi for "redundant offline use"

Hi,

I have some maybe unusual questions for you...

My background: I am an Electrical Engineer with sound Unix, embedded systems (and IT Security...) knowledge.
I am also a sailor and I am planning and preparing for a longer cruise with my sailing boat.

I am currently equipping my boat with the necessary components to spend a prolonged time offshore which includes some challenges for the energy management and also calls for redundancy of the systems on board. When offshore, I need to make sure that all important systems are running prorperly, and if a system component fails when on the ocean, I need to be able to fix it myself - completely offline.

There are some important (but non-critical) components on the boat which I would like to automate using a Raspberry Pi and a UniPI board which I already bought.

When searching for software solutions to simplify or abstract interfacing with the hardware I came across REX Control System. After some research and reading the documentation it looks very good to me and I would be interested in setting up my system using REX Control System.

However, before I invest time and money on this solution I have some questions regarding the system in particular with regard to redundancy and replacement of components.

* Licensing and „business continuity“
As I wrote I will be offline for prolonged periods when traveling. If something fails while being offshore I need to be able to fix it myself and without any online connection or hardware supply.

This means to prepare for outages with the automation system on the Raspberry, I will
- carry at least two spare Raspberry Pi boards in sealed bags
- carry several spare Micro SD cards
- the Raspberry Pi will be attached to one large USB HDD drive for non-automation purposes (Music library, image storage, backups etc). I will rotate several USB HDD drives for redundancy purposes.

If the SD card fails, the Raspberry dies or a HDD crashes, I will swap the components out (which is easily done with this hardware setup) and replace with a spare.

QUESTION:

I noticed there seems to be some very tight licensing scheme with regard to the hardware involved. Could you please give me an indication if my planned usage scenario will work? Will attaching/detaching additional USB HDDs, replacing the OS Micro SD card or completely swapping the Raspberry Pi render the system non-functional with REX Control System?

If yes, are there any mitigations possible to prepare for this?

* Release compatibility
I plan on using Raspbian based on Debian Jessie. From the documentation it seems that this is not yet supported. Is Jessie support planned and if so, when?

* Functions/modules

I will basically only need the standard library.
From the advanced function set I do not need anything - with the single exception of the external program call „EPC“ function which I will need to call external scripts.

I possibly will need the Modbus TCP module to access a Victron Color Control GX device (optional).

Given all these requirements, does the REX Control System fit my needs? And if so, what is the required license and cost?

Thanks and best regards.

jaroslav_sobota

Administrator

Registered: 2015-10-27

Posts: 535

Re: Rex Control System on Raspberry Pi for "redundant offline use"

Ahoy ;-)
thank you for your interest in the REX Control System. Very unusual project, but very interesting!

Here the answers:

• attaching a USB drive does not affect the licence

• the licence is bound to the Raspberry Pi AND the SD card

• you can use multiple SD cards with one Raspberry Pi but you will need separate licence for each SD card - in this case you buy one licence and I will generate the remaining ones for you (all this must be done BEFORE you leave)

• you need a separate licence for each of your Raspberry Pis - in this case you have to buy as many licences as many RPis you want to use

• with e.g. 3 RPi and 6 SD cards, you will have 3x6=18 licence keys, which will allow you to use any combination

• once you have the licence keys, each of them can be applied without Internet connection

• the licensing has nothing to do with the UniPi board

• you can already install and test REX on Jessie, see this post (so far there are no Jessie-related problems reported) - an official release supporting Jessie will be available in Q1/2016

• the license is valid for all versions of Linux

• see our e-shop for pricing - you will use REX Modbus or REX Advanced Modbus depending on your decision about the EPC block - http://www.rexcontrols.com/products/rex … spberry-pi

• you can exchange data with external programs using UDP connection on localhost (REXLANG function block) or you can use SILO function block to exchange data via text files on disk - both options are available with standard licence but both of them require some programming - if you need a straightforward solution, you have to buy a licence for advanced function blocks

• connection to Victron Color Control GX via Modbus TCP is possible (provided you have a licence for Modbus communication)

• RexCore can start from a read-only partition on your Raspberry Pi (important for reliability!)

I hope I have answered all your questions and I believe that the REX Control System fits your needs.

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