Selecting a graphical user interface (GUI) for an embedded design involves a number of considerations—price, performance, system costs, and supported hardware, among others.
We’ve grouped all the considerations under two overarching factors that you should keep in mind when considering your GUI selection: the market positioning and the development cycle.
Market Positioning
While the technical aspects of the project are vital, understanding the client’s end-goal for the product in the marketplace is key to defining the parameters for a product or device’s design. These parameters—including price point, level of performance, and the device’s reliability—are part of the market positioning for the product.
Estimated price of the unit
The manufacturing cost of a unit is calculated based on a variety of factors, including the bill of materials (BOM)—that is, the raw materials, parts, components, and the quantities of each needed to manufacture the product—as well as the license costs of the GUI, and the development process itself.
If the intended market is price sensitive and a lower price-point is desired by the client, then that limits the kinds of choices that can be made about the BOM. We can choose only a low-cost microcontroller (MCU) comprising a smaller internal memory, for example, coupled with a lower resolution LCD screen. In this scenario, there might be no option for external SRAM or SDRAM, and no external flash memory capability.
In these kinds of low-cost scenarios, saving memory is crucial. The GUI chosen must therefore have a higher efficiency and lower memory footprint. But this means the GUI won’t have many fancy widgets, and might in fact require some custom-built widgets to meet the product’s special requirements.
Required performance
If the project is not restricted by the budget, and instead needs to focus more on performance, the engineer will be able to choose a high performance MCU, which is normally equipped with a graphics module.
Such MCU’s are available from the STM32H7 family of chips, for example. They have a built-in DMA2D module that can move pixel data from one memory block to the frame buffer without MCU interaction. This feature can significantly increase performance.
With higher graphical performance, the MCU is able to drive a higher resolution LCD screen and to display more complex items in the GUI, including pictures and videos.
The higher the resolution of the LCD screen in use, the larger the RAM needed. It is expensive to implement a large RAM inside the MCU, and a more economical solution is to add or expand external RAM. However, this has the drawback of increasing BOM costs, so the trade-offs need to be weighed.
Reliability
Reliability is another important factor that needs to be considered when choosing a GUI.
In a safety critical project, for example, it is important to make sure that the GUI is both stable and safety certified. Take the example of modern automobiles: as more and more cars are equipped with full-glass dashboards, the GUI needs to be incredibly stable. If the dashboard were to black out during driving, it is very possible that an accident would result.
Some GUI’s, like GUIX, have already passed multiple safety certifications. Choosing the right GUI for your application can save you the time and effort needed to pass relevant certifications.
The Development Cycle
The right GUI, along with relevant design tools, can significantly speed up your development cycle and help make the entire development process go more smoothly.
GUI design tools
Normally, commercially available GUI’s are equipped with a graphical design tool. Some GUI’s, like Crank, have a high-end integrated development environment (IDE), which allows the artwork designer to create animations easily. Such an on-board IDE can dramatically reduce the development time.
However, graphical design IDE’s are not normally free. Any planned commercial use (such as in development of a product for sale) will come with licensing fees. This needs to be factored into the choice of GUI. If the project has a limited budget or low target price point, then GUI’s using only free or low-cost IDE’s will be your best option.
Development language
In recent years, more and more products feature user interfaces with animations and complex interactions. Some GUI’s have accordingly begun to use object-oriented programming (OOP) languages like C++, or scripting languages like Python and Lua, to support these demanding features better. More complex development tools increase the barrier to entry, so the learning curve for using a particular GUI should be taken into consideration when choosing which one to go with.
Ecosystem
The GUI is a key part of the project, but it is only a part. Incorporating middlewares—software that enables communication between an operating system and the applications running on it—is also a necessary component in the development cycle.
Relevant third-party middlewares to be used might include the USB library, the file system, and even the operating system, since it can be far more cost-effective than to build everything from scratch.
When choosing a GUI, be aware of whether it is part of a software ecosystem that provides mutual support amongst a variety of middlewares. A GUI that is part of a rich ecosystem will mean fewer complications when it comes time for integration of the different pieces of the project.
This article is the second in a series about NeuronicWorks’ approach to design for embedded. The first article, Designing UI for Embedded Devices, can be found here.
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