What to consider when incorporating an intelligent touch screen display into your product

Markku Rihonnen
Global Products and Business Development Manager
What to consider when incorporating an intelligent touch screen display into your product
Gone are the days of rotary switches, push buttons and seven segment displays. Incorporating touch screen displays into embedded designs is the trend, accelerated of course by consumer adoption of the smartphone.

These buttons and switches are being replaced with more colorful and easier to use touch screen displays. The touch displays add a more aesthetically pleasing look and intuitive interaction to a wide variety of commercial and industrial products, and this explosive adoption is reflected in the global market forecast (http://www.strategyr.com/blog/blog-post.asp?bcode=MCP-7725) for touch screen modules which is expected to exceed $40bn by 2024 according to Global Industry Analysts Inc. Actually, touchscreen technology dates back longer than we think, first written about in the sixties by E.A. Johnson of the Royal Radar Establishment when describing the application of touch technology for air traffic control systems. It was probably never envisaged back then that today’s white goods, electronics and kitchen appliances would increasingly use intelligent displays to monitor and control everything, from how you want your coffee, to controlling settings on your washing machine.

Adding touch screen displays actually solves a number of issues with white goods or other industrial products. Removing buttons and rotators that collect dust and allow ingress of moisture and particles will invariably lengthen the lifetime and reliability of the product. Using a glass overlay on a capacitive touch screen allows the designer to keep a tight seal against water and dust. Extensive development has been done on early touch displays, ensuring any number of buttons, wheels or sliders can be imitated on the display, and leveraging the legacy buttons gives the overall user experience a more intuitive and natural feel.

Committing to the right LCD display for your product can be a difficult task and establishing the perfect display and user interface can really work to strengthen a brand or product in the market. There are a number of things to consider when making this decision, but most importantly there are two routes to adding a display to your product: either custom design a discrete display or use an off-the-shelf display module.

The attraction of developing a custom discrete design may give complete control of bill of material costs and thus a significant reduction to the cost of components, with the expense to increased engineering development and time to market. Development will typically take 4-6 months for an experienced engineer.

A discrete design would need to consider a larger number of components to control the display. A microcontroller will need to be selected that will compose and store images to be displayed in the frame buffer. The buffer is volatile memory, which temporarily stores each pixel before shown on screen. The size of the frame buffer is dictated by the size of the screen. A separate display (video) controller will write to the display at a rate of 60Hz. Screens below 4.3 inches typically include their own display controller IC but larger screens will need their own display controller added to the design. Today’s advanced MCUs do sometimes incorporate a display controller and possibly a frame buffer memory as well. But as you would expect, these devices are more expensive, which can often exclude them from the design if there is an alternative available. This means that discreet design can make the project more costly and complicated than originally planned. Separate display controllers typically have frame buffer memory on the die, so the MCU must be able to run the display and frame buffer tasks in addition to the core application.

Primitives need to be written to allow icons, fonts and stored images to be written to the display. These include basic graphic functions such as lines, circles and boxes. Layered on top of this is the screen mapping the touch interface versus the location of these buttons and circles. So, although implementing a discrete design can be the preferred option due to low BOM, it does need to be balanced against the time and additional cost to design it, so time to market is a key consideration.

With all this in mind, using an intelligent display module can be an attractive alternative. These modules typically feature an industry standard interface for communications to the host as well as their own microcontroller. In addition, all the drivers, primitives and GUI functions are already developed and tested. As well as this, the module can pick up all the display tasks from the MCU so that all the host’s resources can all be dedicated to the application.

An example of a suitable off-the-shelf intelligent display is the 4D Systems 4.3-inch gen4-uLCD-43DCT-CLB. When designing you need to consider the features that include most of the commonly used interfaces. This capacitive touch screen controller offers a range of GPIOs, including PWM, SPI, I2C, Quadrature and ADC inputs. A microSD slot provides FAT16 storage for graphic images and storing data.

Choosing the right display for your application needs careful consideration. Discrete designs are more suited to much larger mass manufacturing situations where the additional engineering and delayed time to market can be easily amortized across the total cost. Engineers must consider whether the project timescales and cost can be accommodated by a discrete design approach. However, intelligent display modules and their associated design tools can significantly speed up the design process as well as deliver a professional look and feel to your product. And with the predictions for touch screen requirements in all futuristic applications such as interactive table tops, smart homes and IoT enabled devices indicated as demonstrating “steady proliferation,” it’s lucky that E.A. Johnson did the groundwork for us 50 years ago.

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