Designing HMIs for Displays

14th September 2022

As a follow up to July’s popular post on the graphic design process here is a more in-depth look at designing HMIs for displays. Most people use a Human Machine Interface (HMI) System on a daily basis, from smart phones to the dashboard in the car, to the stop bell on public transport. They are an important part of everyday life.

But they are a complex unit and can encompass all the elements a person will touch, see, hear, or use in order to perform specific functions and also to receive feedback on those actions. They tell us we need to do something, provide us with data and warn us something is wrong as well as delivering and receiving information from other networked systems.

People are so used to using HMI systems that instantly users know if something is not intuitive or is not user friendly and this can have a massive impact on the perception of the entire system.

Therefore, to be effective, it is up to the designer to have a very clear idea of the objective of an HMI system as well as an understanding of the users and their skills and expectations.  It is essential that the design process starts with a conversation and a lot of questions to gain a firm understanding of the context the HMI will be used in.

When designing an HMI display there are two key concepts to keep at the forefront of all discussions: usability and simplicity regardless of how complex the data or the underlying machinery is. That is where getting to know the client is key.

Context is everything

When identifying the foundational context for an HMI display it’s important to understand:

  • Who will use it?
  • What will it be used for?
  • Where will it be used?

Additionally, the answers to these can have a number of nuances which can greatly affect the final design.

Who will use it?

Understanding the operators is the first element of a successful HMI system. It is important to know how skilled they will be, as well as what level of information they will require access to.

This determines whether there should be different levels of access for operators, supervisors, or maintenance staff. So, it’s important to know what each level of operator needs to do their job.

This can reduce unnecessary data available on the display which can be overwhelming and can result in human error.

What will it be used for?

The goal of any HMI system is to communicate the necessary information to achieve the intended task. To achieve this means knowing what that task is and what information will be required.

For example, will it require a single function or multi-function display? Will there be a single screen or multiple screens each displaying different information?

Any special requirements for specific users also need to be considered such as visual, auditory, or tactile feedback. Would touchscreen be inappropriate, or would toggle switches be preferred? Would a red light or alarm be better to indicate a fault?

Where will it be used?

The type of environment that the display system will be used in will obviously affect the design. For example, will the unit be exposed to moisture, extreme weather or temperatures, UV radiation, vibrations, vandalism, or rough use characteristic of harsh environments? Will it need to be used in bright sunlight or dimmed light?

Knowing the answers to these can determine whether touch screens will be effective (especially if the operatives have to wear gloves), if the colors used are appropriate and what types of screens as well as the industry IP ratings are necessary to ensure its continued function.

How will the display function?

Of course, there is more to designing an HMI display than knowing who the operators are, where the display will be used and what the primary function is, although they are a foundation for an effective system. There are, however, a number of other things to be taken into account regarding front and back-end functionality:

  • Color schemes – The colors used on the displays are more than aesthetics, as getting it wrong means the colors may not be readable and could potentially confuse the operator. Colors also need to be clear and intuitive. For example, red is usually used to indicate stop/failure or a fault and green for all clear. Adopting a simple system, with minimum alarms and flashing lights will prevent user error.

Whatever color scheme is chosen it should be consistent across all screens and should be accompanied by clear labelling to relay information. This means avoiding acronyms unless all users will understand, as well as providing an indication of any steps the user needs to take.

  • Simplicity – To aid useability, the screens should be easy to read, without too much information. All information displayed should be relevant and labelled appropriately.

If utilizing multiple screens include easy to access menu buttons, as well as an easy way back to the home screen. The more intuitive a screen is to navigate the less errors occur.

  • Useability – The screen layouts should be user-friendly, so like should be displayed with like to avoid too much flicking between screens.
  • Style – Each industry has an expected look and style and this needs to be taken into account in addition to the functionality. For example, in the marine industry, where the consoles are for high-end vessels, the style has to match the price-point and final end-user.
  • Industry Standards – Each industry has their own set of standards, and these need to be considered in the designing process. Depending on whether the device is for use in the EU or the US means specifications could come from ANSI, IEEE, ISO, or others, as well as taking into consideration environmental sealing requirements (IP rating) against moisture, cutting fluids, oil, and dirt.
  • Data Transference – The key to an HMI system being successful is up-to-date accurate information and therefore knowing how this information will be received (and sent) is vital. Will it be a combination of digital and analog devices? Or completely digital? Will it be transferred using a CANbus system?
  • Robustness – The value of an HMI display system is only considered good when it is working, so ensure it is able to withstand the environment it is to be operated in, as well as lasting for the duration of the equipment lifecycle.

There is a lot to think about when designing the perfect HMI display unit, but the more information gathered up front can make the designing process easier and result in a more successful product.

Here at Veethree, we are able to design your HMI display system from scratch or add bespoke software to hardware already in stock such as the:

  • R3 three-inch CANbus Display which is great for using in bright sunlight, is IP 67 rated, and supports CANbus (including SAE J1939, NMEA 2000 and NMEA 0183), as well as having both analog and digital inputs.
  • T7i seven-inch CANbus Display which can operate in extreme temperatures, is IP67 rated, and has a full color LCD display screen.
  • T5 five-inch CANbus Display has both digital and analog inputs, is IP67 rated and is compatible with J1939 and NMEA 2000.

To find out more about the products head over to the product page or email the team to discuss a bespoke project.