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Digital-Physical Product Design: How to Approach Process

It’s tempting to think of digital-physical products as simply a more capable evolution of familiar physical ones, but the truth is that adding digital intelligence can often create an entirely new set of interactions, expectations, and use cases.

Think of the Roomba, which adds sensors, motors, and basic learning capabilities to the humble vacuum cleaner. You don’t use it, or even think of it, in the same way as a vacuum cleaner, but as something closer to a robot or a small pet. With a Roomba, vacuuming is no longer an activity but an ongoing process — a fact that Roomba’s parent company, iRobot, struggled with initially before getting its design and marketing right.

There are, in fact, some fundamental differences in how you go about designing physical products that incorporate digital features — a fact that we addressed in my earlier article, “7 Principles for Designing Great Digital-Physical Products.” In our experience, the best approach comprises three major components: Assessing the use situation, finding the right blend of digital and physical, and smoothing out the transitions between them (a process we call “hiding the seams”).

Here are brief summaries of how each of these works:

1: Assess the Situation

The first component of good digital-physical product design is also the part that most closely resembles other product design pursuits. Whether you’re creating an app, a toaster, or something in between, you need to know who you’re designing for, what their environment looks like, and what their expectations and limitations are.

The standard practices of understanding environment and ergonomics, and of observing and analyzing physical workflows, are more or less the same as in physical product design, albeit with a larger toolbox to pull from when finding solutions — designing for users with limited physical dexterity, for example, is easier when digital interfaces can be used alongside physical ones.

Expertise levels and social context, however, take on greater importance. Adding digital capabilities can expand a product’s utility, but also its complexity, so matching the interface to the user’s expectations and skill level becomes even more crucial. In some cases, it may even be worth designing different interface modes, to allow users to fine tune the complexity themselves. We’re also still in the midst of developing social norms around using digital devices in public, making it all the more important to know where the product is likely to be used, and with whom: a “beep” with every pressed button is crucial in a loud garage setting, but mortifying in a theater or library.

Assess the Situation: Checklist

  1. Observe and analyze physical workflows.
  2. Understand use environments and parallel activities.
  3. Determine ergonomic requirements.
  4. Understand user types and expertise levels.
  5. Consider social context.
  6. Catalog the “actors.”


2: Get the Right Blend

One of the things that makes digital-physical design so hard is that the two domains overlap in so many ways. A digital slider replicates a physical one. A camera can “zoom” by moving lenses or manipulating pixels. A latch can close with an electronic, motorized cam, or the manual turning of a bolt. Knowing when to use which is often the difference between a satisfying product and a frustrating one.

That’s why it’s important to be systematic about identifying use cases and interactions, and consider the entire list of tasks before making decisions about how to accommodate them. In general, digital inputs and feedback will give you more flexibility than their physical equivalents, but less reliability and a longer learning curve, so bear that in mind when looking at your prioritized list of interactions.

Digital inputs and feedback will give you more flexibility than their physical equivalents, but less reliability and a longer learning curve.

It’s also worth keeping your own background in mind as a designer. Both interaction designers (IxD) and industrial designers (ID) are called on to tackle digital-physical products, and both can do an excellent job. Industrial designers tend to be hampered, at least initially, by their lack of familiarity with the range of options available to them, often missing more elegant solutions or throwing up their hands at rapidly building complexity.

Interaction designers, on the other hand, often default to a screen-based interaction, even if a physical one would be more direct and obvious, and keep the user more focused on the task at hand. There’s no miracle cure for these biases, but recognizing their existence is a good place to start.

Get the Right Blend: Checklist

  1. Prioritize use cases and key interactions.
  2. Define user inputs and feedback. Determine which should be digital, and which physical.
  3. Define automated inputs / algorithms.
  4. Define digital / physical communications (sensors).
  5. Generate parallel digital and physical workflows.


3: Hide the Seams

It’s easy to make a digital-physical product: just take a faucet/thermostat/car dashboard/etc. and bolt a sensor or touchscreen onto it.

Making a good product, on the other hand, takes far more effort. There’s nothing natural about shifting between the direct, what-you-see-is-what-you-get experience of a physical interface and the flat, flexible, endlessly dynamic experience of a digital one. Easing that transition is perhaps the greatest difference between digital-physical products that make sense, and those that feel like two products duct taped together.

To turn the two halves into a pleasing whole, approach the design process as a “cohesive mental model.” Consider the physical and digital components of the user experience as a single entity, rather than a pair of parallel streams. A single designer should have ultimate responsibility for the entire workflow, in other words, and user testing should combine both streams.

A single designer should have ultimate responsibility for the entire workflow, and user testing should combine both streams (digital and physical).

“Interaction metaphors” are something we use to make the unfamiliar more familiar, which often means couching digital interactions in the language of physical ones (just as our desktop operating systems use “files,” which go into “folders,” which can be thrown in the “trash,” and so on). This is also the impetus behind developing a consistent design language and harmonizing its graphical aspects with the industrial design of the product.

Because users will often be jumping back and forth between tapping buttons or touchscreens and physically manipulating knobs and switches, it’s important to make these as unified as possible, through iconography, terminology and even typography. We’re accustomed to using physical and digital products, but not to combining them — it’s your job as a designer to offer regular reassurance that this is all a part of a coherent whole, even if the technology behind each interaction is vastly different.

Hide the Seams: Checklist

  1. Support a cohesive mental model.
  2. Choose appropriate interaction metaphors.
  3. Map inputs and feedback naturally.
  4. Consider input / feedback relationships & micro-interactions.
  5. Develop consistent design language across digital and physical.
  6. Marry display and feedback with overall industrial design.

Better Than the Sum of Its Parts

In some ways, the above guidelines are just Good Design Process 101: Empathize with your user, be intentional, test, and iterate. But it’s also uncharted territory. Digital design has several decades of expertise and best practices behind it; industrial design has a couple of centuries. Asking these two full-fledged disciplines to play well together is no easy task, but it’s one we can no longer avoid.

The era of smart-everything is here, and it’s up to us, the designers, to make sure that they don’t get in each other’s way. And if we’re very good, we might even create something that’s better than the sum of its parts.

Learn about our Digital-Physical Design expertise.