Electronic human machine interface (HMI) technology goes back as far as the 1940s with the punch card batch interfaces from IBM. Today, when you think of user interfaces, you may think of smartphones, tablet computers, ATM machines, or any other consumer device. There have been an astounding number of technology improvements in interface technologies. These technologies are frequently used in medical applications to make devices more flexible, easier to use, durable, and efficient.

Figure 1. High-reliability HMI designed with a rigid circuit board.

Today's medical devices can pose a lot of challenges for designers when they are designing and specifying human interface technology and functionality. Examples of challenges that designers may face could be anything from the environment in which it will be functioning, to the warranty/maintenance programs. All must be factored into the design at a very early stage in order to create an application that is safe, reliable, and user friendly.

The advancements in technology have made it much easier and much more cost-effective to incorporate new functionality into every design. Specific functionality such as touchscreens, remote monitoring, capacitive touch switches, or software/firmware that can be customized at a moment’s notice are all now commonplace in the newest HMI designs.

High-Reliability HMI Designs

As the cost of healthcare continues to rise, medical professionals are looking for devices that are rugged and can extend the life and minimize the maintenance costs of their operation. Being reliable doesn’t necessarily mean the device will be overly costly, as there are ways to incorporate ruggedness into a machine interface design. A few examples would be:

  • Incorporating a rigid printed circuit board (PCB) into the design to attach LCDs, switches, or other components, as the copper and solder joints provide much more durable connections and a solid backplane for the interface (Figure 1).
  • The use of capacitive touch membrane switches versus mechanical switches, which can get damaged and wear out over time.
  • Selecting stack-up materials that create robust designs that can withstand whatever environment they are placed in. Choice in components, touchscreen types, and adhesives can dramatically add or take away from a robust design.
  • Placement of the components on the interface will also affect the longterm functionality of the device, as the most sensitive components need to be protected from potential contamination. Working with a supplier that has significant experience in this area can save you from redesign after the product goes into use.

Understand the RF/wireless/EMI aspects of your product and how to protect your machine interface from being affected. With the Internet of Things (IoT) being incorporated into almost anything, these factors need to be managed when creating a design that needs to work for years to come.

In regards to an operating environment, most medical device interfaces must have some type of IP rating as they are likely to come in contact with bodily fluids that will require the device to be cleaned and potentially sterilized. Understanding the rigors of the process will allow your design requirements to have some, if not all, of the attributes above.

Incorporating “SMART” into Your Device

Making something SMART can mean different things. For the purposes of this discussion, we will focus on two specific ways to make your medical HMI SMART, through programmed user guidance and remote monitoring.

These technologies have existed for years, but advancements have now made it possible for wireless capabilities, and the cost of manufacturing is more reasonable. It is clear that SMART devices are becoming increasingly common in medical applications.

Programmed User Guidance

Programmed user guidance means incorporating functionality into the interface that visually guides users through the proper sequence of events to get the desired results. This will not only improve the user experience, but improve safety and reduce operator error. One downside of a full touchscreen solution is the overall cost of a reliable touchscreen that can be used in harsh environments and with the gloves that are used daily in the medical profession.

Some companies are developing medical devices that have a very low-cost interface on the device itself, and are having users connect to the device with a smartphone app that allows them to control the device. The solution has been gaining traction in non-life-critical applications as the battery life of the smartphone can cause the device to stop working.

Capacitive Touch and Backlighting

There was a time when in order to get features to light up on a machine interface, you had to use LEDs that were mounted close to the feature to be lit. That required more real estate and therefore added more cost to user interface designs. It was also difficult to enhance a user experience with backlighting, as it wasn’t easy to keep the light from bleeding through the feature to other areas of the interface. The invention of side-firing LEDs and light pipes helped counter the problem, but the higher costs kept the technology from becoming mainstream for medical applications.

Figure 2. Medical device user interface utilizing lighting technologies.

Now, through the use of ultra-thin planar light panels where features and light channels are pressed into the film, devices can improve their functionality by utilizing lighting and capacitive touch integration. This is done by effectively developing a user experience where certain buttons light up, turn color, or turn off when particular inputs are detected (Figure 2). Using clean and isolated visual feedback allows engineers to take the user through operation of the device with real-time guidance.

Integrated Firmware/Software

Most leading-edge companies in HMI design and manufacturing do much more than just create low-end hardware like membrane switches and graphic overlays. A big part of the vendor’s responsibility is to not only develop the hardware, but also develop most of the software/firmware to operate the device.

The interface can take inputs from the device and trigger a message to the user. This can be anything from:

  • Serial input/output interface
  • Bluetooth and wireless communications
  • SD card and USB communication
  • Pressure/flow switches
  • TDS meters
  • Pressure transducers
  • Temperature sensors
  • Voltage/current sensors
  • Battery status
  • Temperature/humidity sensors
  • Valves and mechanical switches