Things I learned in designing interfaces for physical products
UI elements will live together, not always in perfect harmony
As digital interfaces enable so much flexibility for a designer to create guidance and relevance in what's important in specific contexts, it changes a lot for physical product. You are pretty much limited to what hardware component you are working with, which in my experience impacts a lot the visual interface in terms of how to display things in a way people can easily scan when they look at it, but also make senses in a logic of use.
What does that mean for your design?
Unrelated functions will appear together, which may lead for errors while performing a task due to pressing a wrong button. Check the remote control, it is possible there are a bunch of buttons that you won't necessary use, but well, there they are, increasing the cognitive load because in physical interfaces you can't just hide things according to the context of use.
Visual hierarchy REALLY matters
When everything is visible for the user, the choices made for visual hierarchy are really important. How people's eyes scan a interface and those UX psychology laws seems to have an effect, however it will be even more needed because the interface is an extension of the product itself. So the shape of the product will also be part os how ones reads the UI elements.
What does that mean for your design?
The guestalt principles will be applied, so the positioning of the UI itself affects its perception, once the user sees the interface as a whole, it will look for the details in buttons, labels, titles and graphic elements to guide himself. So in this moment you wanna play with ordering and grouping functions, by using colors, sizes, sequence. So
Selling features…
…is a real thing. If there is one thing I'’e learned is that people are users as much as they consumers, and they have different expectations when they are in these different modes. In the consumer mode they will want the airfryer with 58 different frying modes, but when they are users, they just want to turn on the fryer and not think much about what frying type they should set up to have the perfect chicken.
What does that mean to your design?
These features usually need to be visible in the UI so consumers are aware of them. This will affect the UI because as a designer you might want to create a visual hierarchy that enhances the core functions of the product, the ones that are daily used. However the product also needs to be sold, so you might have to rethink the UI and enhance a feature or two that might not be that interesting for the user but is a delight for the consumer.
Hardware is a limit
You may have the best concept for enabling an amazing experience for your user, however it will need to fit to the hardware of your project. Depending on production scale of your hardware, it may cost more or less, well, and price is a great driver for projects decisions on using one harware or another one. If you are lucky you may be able to design a UI where a hardware will be produce to assemble it…but still you will need have a mind where you make this PCB more modular and able to fit different projects.
What does that mean for your design?
This choice will drive you on how many buttons and feedbacks you will have at you disposal and that means you will have to design around it. Sometimes the feeedback won't be clear, other times you will have enough to make the user pay attention for where you want it. I used to be super happy when I had a interface with button with LED light feedback. I did, however, had to rethink a flicking behavior on one of it because there wasn’t enough memory on the hardware. C’est la vie.
Feedback
As I have mentioned, hardware is one important thing to have in mind. Usually it is more feasible to have more buttons (keys) than to have a good feedback.
If you look at the UI of my microwave you will see a lot of functions, the keyboard and cancel/start buttons. The only feedback that is possible to use is a display designed to show numbers and a beep sound. So as a user, I know something is selected because the displayed changed and a sound confirmed something happened, but it may not be enough. How do you cook a cake if the UI only shows me 5 minutes?
What does that mean for your design?
You need to find ways for creating consistency and patterns that are not written in google material design. You will find how to communicate to the user he is pressing a wrong button (because remember, buttons are printed so there is no hiding there), and you will have to make choices about the amount and what kind of information you are showing.
Yeeeeah, probably there are buttons that would require a user guide to understand what they do, but a simple label printed below an icon is all you can do so you don't overload the interface with too much information (side note: remember if it is being printed there are also limitations with the printing process that will affect your choices).
Aesthetic matters…
…and sometimes it is not the best for usability and vise versa. In the end it comes to decisions on balancing pros and cons.
Check this remote control. First, I am assuming it is for an air conditioning, and secondly, I am also assuming the AC has some display for feedback. This will mean for the user that he will have to be close to the AC every time he wants to change the temperature because there is none on the control…which is not quite what people expect for a remote control…
What does that mean for your design?
For physical products the visual appeal is really important, specially since most of the time people will live with products in idle mode. But sometimes to create a good usability you will compromise some of that beautiful aesthetics.
You don’t have a future release, you HAVE to think upfront
To finish it, one thing to have in mind is that it does not have a second release. A second release means to change the production and it have a big scale of complexity. So if there is some wrong you figure out too late, it will have a cost.
Even if it is small software change you will fix in the next batch, chances are the user guides have already been printed, so that change may impact on them. I have encounter situations where I was asked to not update one icon en a membrane of a display, because it would create two very similar parts with two different codes, and it be trouble during assembly line.
What does that mean for your design?
You don’t just sketch UI layouts and think later on how it will behave. You sketch them having an idea on what kind of interactions you will be able to do with the technology (hardware) you are working with. You propose at the same time you think about all the use scenarios, specially border cases, so you don’t get into a situation where you find out you needed and extra LED but it is too late to implement it.
These are things I learned along my 4 years designing UIs for physical products. It is funny because even among designers people don't seem to relate the UX principles applied to non digital products, but there are a lot of interactions in these product's UI.
Also a lot of the content relate to UX is most directed for the digital, so it has been a long way adapting information and learning from others experience, specially from Mayra Laska, my former coworker who shared most of her background and perceptions, specially that a user is both consumer and user :P
