FEAT
ATURE
SWITCHES, DISPLAYS & UI’S
HMI DESIGNS: THE GOOD, THE BAD & THE UGLY
By Paul Jiao Shouwu, Bridgetek
sensing technology employed. For instance, specifying a proj
ojected capacitive sensor, with an easy to wipe down
prot ective screen, might be called for. In less challenging circumstances, curbing the bill-of-materials costs may be the priority, making res tive t ouch preferable. If operators haven’t received in-depth training, or the HMI is int ended for individuals that will have no previous experience of using it, then the design should clearly reflect t his. The regularity with which different operat ions are executed should be ascertained, and layout optimised accordingly . Likewise, ergonomic aspects must be taken into account - display size; dist ance from the operator; where their line of sight will aim, etc.
T
he prevalence of human machine interfaces (HMIs) based on
touchscreen displays is increasing
all the time. As well as being almost obligatory in consumer goods, they are now commonplace in domestic appliances, home automation systems, vending
machines and industrial equipment. These HMIs are no longer just another feature - often, they represent the fundamental reason for a product’s success.
Plenty of examples exist where t ouch- enabled HMIs have been the defining attribute allowing certain products to commercially outperform rivals that had the same (or possibly even better) functionality. If the HMI is inherent ly enjoyable to use, t hen it will be much better at showcasing the associated product’s feature set, and will make it more appealing to customers. Conversely , if it causes user frustration, then this will be detrimental t o the market uptake of t hat product.
A poorly thought-out HMI design may not just impact on product differentiation though; it can potentially have far more serious implications, resulting in the operator’s safety being compromised. There are well-documented cases of industrial accidents occurring that stemmed from errors of judgement
stemmed from errors of judgement made because of an inadequately realised HMI. Each icon displayed should therefore be distinct and easy to recognise, thus removing the risk of it being muddled up
18 MAY 2020 | ELECTRONICS
with other icons. The data that an operator needs to access must be rendered in such a way that it is quick and straightforward for them to underst
o understand. The reaction
times required mayimes required may be very short, so there should be no prospect of something important being accidentally overlooked because it is not in a prominent enough position, or its meaning is ambiguous. Also, pages must be quick to load, with no unwanted latency.
Where t he HMI will be located has to be given sufficient considerat ion. If it is for a public information unit sited outdoors, or incorporat ed into an electric vehicle’s instrumentat ion cluster, then ambient light variations over the course of the day will need to be dealt wit h. When being deployed in an industrial context, presence of smoke or steam may also impair visibilit y . Hence, the size, shape and colouring of buttons, dials and gauges should be bold enough to mitigate low-light conditions. In harsh application settings, t he effect of vibration on the HMI may need factoring in. T he clarity of cont ent shown on the screen will require greater augmentation in such situations. In a medical environment (to combat t he spread of bacteria) or an industrial processing plant (where there are hazardous chemicals), operat ors may have t o interact with HMIs through thin gloves. In each of these scenarios, thought should be given to the touch
Figure 1: Examples of the many widgets supporting Bridgetek’s EVE HMI development platform
Among the many things t o contemplat e are - what will be the minimum physical dimensions of a particular button (and will the specified display ’s size/resolution be ample enough t o support t his)? Then, where should it be placed in respect t o other items on the screen to avoid distraction? Will sliders or dials present more efficient options for certain control functions? The sound out put can also be an important aspect of user interact ion. Inclusion of animation should not be discounted either, as this can prove invaluable in providing more compelling content.
Bridgetek
www.brtchip.com
Modern product development cycles are subject to acute pressures, with huge impetus on exploiting short-lived windows of opportunity. Alongside this, there are usually budgetary concerns – though performance needs to be boosted and feature sets accentuated, the associated costs must still be kept in check. Bridgetek’s Embedded Video Engine (EVE) platform transforms all the different HMI elements into an object form. These objects are rendered more rapidly and require far less data storage capacity. Component costs are consequently lowered, as is the board space taken up and the power consumed. EVE makes HMI construction much easier to accomplish, with an ecosystem of related software tools that rely on a simple drag-and-drop approach, and an array of pre-defined widgets. The upshot of all this is engineers don’t require any prior coding experience.
/ ELECTRONICS
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