HMI hardware platform choices
28 May 2019
Small computer boards originally intended for educational use have been enthusiastically adopted for industrial applications. Although effective for fast proof-of-concept work, engineers need to consider how they will ultimately industrialise the finished product and may need to consider porting to a more suitable hardware platform at the earliest possible opportunity. Tim Liou, application & development engineer, Anders, reports
Open-source hardware is gaining recognition as an approach for building cost-effective devices aimed at industrial and IoT applications. Organisations such as the Open Source Hardware Association are promoting the cause and providing services such as certification to help users identify hardware that meets their criteria.
Among companies that are positioning industrial devices such as HMI panels and PLCs based on open-source hardware, some are basing their products on platforms such as Raspberry Pi and Arduino that were originally conceived as educational tools. Several factors mitigate in favour of these platforms: they are affordable and compact, and their popularity means there is plenty of code in the open-source community to help get basic features running.
So far so good, but caution is needed when taking the project forward. Engineers should always consider how their chosen hardware will perform in the target environment, such as whether it is specified over an appropriate temperature range, or whether physical interconnects will withstand expected levels of shock or vibration. If the chosen module is not specified over the applicable temperature range, or not robust enough to withstand hazards such as shock, vibration or moisture ingress, extra costs may be incurred to carry out additional tests or design-in extra protection for the hardware.
Other issues to consider are how the resulting product will perform in EMC tests. Although the chosen board may have passed relevant EMC tests to qualify for CE marking, OEM teams need to ensure the finished product will meet the requirements for their target market. One example is if the system contains a projected-capacitive (PCAP) touchscreen user interface. If the touchscreen controller is an ordinary commercial-grade IC, it can be particularly difficult to satisfy the IEC 61000-4-6 Level 2 or Level 3 conducted noise immunity specifications for industrial or medical equipment. A higher-grade controller may be required, and changes to the board layout may also be needed to achieve the mandatory immunity.
It is also critical to ensure that the module – as a constituent component– will be both adequately supported and available to purchase for the intended lifetime of the end product. This is a given for industrial components, which are typically backed up by a manufacturer’s longevity commitment for as much as 10 years. Consumer components, on the other hand, come with no such assurances and the desired support commitment from the original module manufacturers may not be provided, and could result in costly re-designs halfway through a project’s lifetime.
Moreover, module producers sometimes have to make small changes to their products that can affect parameters such as signal timing or voltage thresholds. Engineers need to know how their system’s performance may be affected but, whereas a vendor of industrial-grade products will likely provide dedicated support to answer such questions from customers, the same is not so easily provided by an educational board producer.
Encountering these issues later in the project, when extra effort is needed to work around them, can prevent reaching critical milestones on time. Having to change the hardware to overcome these barriers can introduce delays and expenses that may negate the expected advantages of using open-source hardware.
Porting the design to an industrial-ready platform at an early stage can be easier than expected. An HMI design expert such as Anders can help ensure a smooth and efficient transition from the initial proof of concept model to a more industrialised and rugged prototype suitable for subsequent stages of development.
To establish a suitable hardware platform for development, a strong choice of application processor is a good starting point. While it is true that some chip makers are focused mainly on the consumer space, where short lifecycles prevent longevity assurances, several manufacturers offer products that are suitable for more specialised industrial or medical applications.
One example is the NXP i.MX6 family. These are available in single-, dual-, or quad-core versions featuring a combination of Arm® Cortex®-A9, A7 and support high-performance interfaces that are popular in industrial applications, such as SATA 2, FlexCAN, PCIe, Media Local Bus (MLB) support for easy connection to MOST or other networks, and MIPI display and camera ports.
These are in addition to the well-known connectivity standards such as Ethernet up to 1Gb/s, USB Host, and multiple ADC channels. In addition to their multi-core scalability, this family also offers flexible graphics options with 3D support and dedicated acceleration engines that outperform the general-purpose graphics support integrated in the processors of low-cost educational platforms.
Multiple variants are available, offering users a wide variety of configurations including some models with a built-in Cortex-M4 coprocessor to offload the main application processor. This maximises flexibility to meet system-performance requirements and budgetary constraints. At the entry levels, pricing can compete favourably with open-source alternatives.
The engineering team at Anders is familiar with this and other families of application processors that provide a suitable foundation for industrial-ready HMI control. They can help establish a suitable hardware platform based on any of these devices, or quickly port a proof of concept model to a platform that can more readily be prepared for industrial use cases.
The opportunity to trim time and cost from a development project by starting with affordable off-the-shelf hardware can be tempting, especially for designers who are familiar with the finer points of platforms such as Raspberry Pi, Arduino, or others. Although they can be effective for proof-of-concept work, problems may arise when industrialising the end product to withstand the operating environment and satisfy mandatory requirements of the target market.
If these criteria cannot be met, a recommended approach is to port the design to more robust, industrial-oriented platform at an early stage of the project. Ultimately this may result in faster time to market and lower development costs. Seeking expert advice is always recommended, to help commit to the best hardware for the intended application at the right time in the project.