Displays How to choose an SBC or COM
Rhett Evans, andersDX, provides advice on the factors to consider when choosing between a single board computer (SBC) or core module (COM)
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PU choice is one of the most critical elements of any display based system. It is the brain of the entire module, driving all the I/O peripherals, display and touchscreen, or at the very least, it is responsible for creating the data that is presented. In an IoT system, its role is to join the I to the T. It connects the Things (like sensors) to the I (the Internet) and provides content for the local display. Processors are normally supplied as a complete single board computer (SBC) or as a stripped down core module (COM). The choice of processor, and the format in which it is delivered, are key decisions. So, what factors do you need to consider when choosing between SBC and COM options, what are the key specifications to look out for and finally what design support will you need?
What iS thE DiffEREnCE BEtWEEn a COM anD an SBC? Choosing between an SBC and a COM is a trade-off between time to market and flexibility. A single board computer is a ready to go instant platform that ships with all the drivers needed in the form of a board support package (BSP). It will have fixed computing, memory, and I/O sections integrated onto a single PCB. A core module (also known as a computer- on-module (COM) or system on module (SOM)) is half-way between an SBC and a discrete microprocessor IC. It offers more flexibility than an SBC, without the much higher development effort associated with a discrete solution. The core module will contain the processor and memory and is then mounted on a separate carrier PCB containing the I/O section of the design.
What aRE thE aDvantagES anD DRaWBaCkS Of an SBC? Clearly an SBC saves a lot of integration effort and development time. It comes out of the box as a fully working solution that just needs to be loaded with the application software and interfaced to the display. The issues encountered most often are size and I/O. Each manufacturer offers a limited range of SBC options with different and fixed permutations of I/Os, size and features. So it is a matter of selecting the most suitable option from the range – you cannot customise the board in accordance with the needs of the application. If a key interface is lacking, then it is sometimes possible to create an adaptor, using the pin header frequently provided. If the board will not fit into the system caseworks, that is generally a deal breaker.
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hOW MuCh flEXiBility DOES a COM pROviDE? The advantage of the COM path is that you can design the carrier board exactly according to your size and configuration requirements, and then connect an SoM to it. Clearly this will take time and design effort, but will allow you to create a board with exactly the I/O that you need for your design and of the right form-factor. You are not left with interfaces that you do not need but cannot get rid of, wasting space. Later on, if the need arises, for example, to add new I/O options, you can simply redesign the carrier board and continue to use the same COM. Equally, it may be possible to upgrade the processor and the memory later without rebuilding the base board, by using a pin- compatible replacement module. There is also a third potential avenue. Some
suppliers like AndersDX with its DX range has developed its own range of baseboards with interchangeable core modules. You can start your development on these platforms, work on the software and in the meantime, develop your own baseboard if you choose to.
COnSiDERatiOnS WhEn ChOOSing an SBC OR COM The decision to choose an SBC or a COM depends on the specific project requirements and sales volume. Whichever route you opt for, the most important specifications are: • The interfaces provided for sensors and actuators (How many are there, and
are they the right ones) • The connectivity options for the
network and Internet. • Support – which can make a big difference
to how long it takes to get your project up and running: (Is there a well supported and robust board support package – how much other help is available for the software developer?) Other things matter too: • Temperature range – will it work in
hot/cold conditions? • Longevity of supply – will you still be able
to get it in ten years’ time? • Power – especially if it needs to run from
a solar panel or battery • Last by no means least is the cost. If a
board is to be sent out into the field in any volume, budget is always going to be a factor.
DESign SuppORt: What DiffEREnCE DOES thE SuppliER MakE? Having drawn up a shortlist of boards that tick the technical boxes, it is well worth taking a hard look at the organisation you are sourcing the board from. A good supplier with a partnership mentality can make a huge difference to your time to market. Here are eight key questions to consider. 1. What is the pedigree of the manufacturer of the board? Do they have a reputation for producing quality, stable products? What long term availability guarantees do they offer? 2. Is there a board support package for your chosen operating system? Does it contain all the
October 2018 Instrumentation Monthly
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