After years inside military jets, the head-up display is taking its place on automotive windshields

Today’s automobile driver receives an overwhelming amount of information pertaining to the safe operation of their car like no time before. Whether it’s a GPS system mapping out precise directions from point a to point b with countless detours along the way, rendering the old paper map to history, or the multitude of warning lights to indicate the vehicle’s health to the driver, to newer features like blind spot monitoring, today’s driver has a lot of indicators vying for their eyeballs. Ensuring that as much of that information as possible can be viewed by the driver while still keeping their eyes on the road is a continuing challenge for car designers.

The head-up display (HUD) is taking its place inside the automotive chassis after years of strictly being used in military jet cockpits. Automobiles with head up displays transparently project driving information directly onto the windshield, at eye level — hence the name — so the driver can read and process that information while maintaining their focus on the road. Better focus means better response time should the driver need to act on that information.

Drivers may find HUDs displaying information such as vehicle speed, rpm, simple navigation directions, and alerts from driver assistance systems including lane departure detection warnings, forward collision alerts, blind spot detection warnings, and on some cars with adaptive cruise control, gap settings may be given. Recent hybrid car models display information pertaining to the hybrid system itself along with other data.

Soon, HUDs will no longer be exclusive to high-end cars; as technology improves and costs come down, expect to see them designed into more small and mid-sized cars, too. According to IHS Automotive, manufacturers expect to design HUDs into 9.2 million units in 2020, up from 1.2 million in 2012.1 With an increasing amount of in-vehicle electronics gathering information for the driver along with increased interest from automobile manufacturers, HUDs are the display technology of the future inside the car.

Real-time data processing unlocks the HUD’s potential
A typical automotive head-up display may use 1.8-inch TFT LCD panels or a projection technology to render data to the driver. LEDs provide the light and color. Information about driving conditions, vehicle diagnostics, and even infotainment — which is typically scattered in a variety of locations within the driver’s periphery vision and usually not directly in the driver’s field of vision (FOV) — are primed for display in just one place, where the driver’s attention is required the most. Taking all the sensor and camera data in modern vehicles and then presenting it to the driver is no small task and requires very robust data processing capabilities.

“With DLP technology, we are working with customers to enable HUDs that can augment reality. If you just think about the application, there’s a lot of real-time signal processing that needs to take place,” says Jeff Dickhart, Product Line Manager, DLP Automotive Products at Texas Instruments. “Getting navigation data from the head unit — you’re comparing that to where the driver is on the road, and then you’re having to project this info as the driver moves and bumps along in a real live environment,” he adds.

As car manufacturers continually improve their HUDs to enhance the driving experience, they seek better graphics processing performance from IC vendors. Graphics processors are usually embedded within the applications processors employed in HUDs. IC vendors are taking their cue from consumer devices, where the portion of the chips going into smart phones that is dedicated to graphics, is growing. “That graphics technology is going to drive all of these processes that will be projected in front of the driver,” notes Dan Loop, Automotive Business Development Manager at Freescale Semiconductor. The company’s i.MX processor family is positioned for the graphics needs of next-generation HUDs because of the scalability of the CPU as well as the graphics processing capabilities of the products to accommodate different vehicle platforms with varying quantities of display outputs. “It’s really a pixel-bound equation,” he continues, “ that will dictate what resolutions those displays can be and how we can process all that info in parallel to be able to render multiple pieces of content on multiple displays at the same time.”

Project the right chips for wider, brighter HUDs
One thing designers can count on with automotive head up displays is change. Dan Loop suggests that as the HUD market continues to grow and resolutions get larger, developers should ask how hard and fast are the customer requirements. “We see things changing dramatically — so the ability to take the processor out and just do a simple replacement to a pin compatible high performance part is a huge value proposition.” 

And as more information becomes available to the driver, augmented reality technology, along with the availability of DLP projection technology, will help provide a wider FOV for the driver — perhaps as much as 10 or 12 degrees versus the four- or five-degree FOV typical in today’s HUDs — as well a farther projection distance for the driver, allowing for more reaction time. First, the designer must consider an applications processor with the graphics processing capabilities that can meet the warping requirements necessary to make correct projection on to the windshield of a given system, which must also include the ability to adjust to the different shapes and styles of different windshields if the HUD is targeted to different cars.

Brightness is also critical because more information is to be presented in the driver’s line of sight. The amount of light the driver receives from the HUD must not compete with or against ambient light. TI’s Jeff Dickhart sees a 5000:1 dynamic range of brightness required in order to achieve a maximum of 15,000 cd/m2 of brightness during the day, and 3 cd/m2 at night for HUD applications. That means selecting optimal LED drivers and operational amplifiers, among other chips. Jeff adds, “In the DLP HUD solution, we actually have a TI Piccolo MCU (that handles) the pulse width modulation of the LEDs to ensure that dimming is well controlled and happens very smoothly so that the driver gets the appropriate amount of light ...That’s an area where care really needs to be taken.”

Down the road
From powerful applications processors and MCUs that handle the data from a growing range of sensors and cameras to the LEDs and LCDs that light the way, the technology is clearly in place to make sure critical information is presented to automobile drivers in an instant and unobstructed way. As processing power increases to allow for even more information to reside in the driver’s line of sight, designers must continually factor brightness, distance, field-of-view, and cost to deliver information not only safely and efficiently to the windshield, but even to overlay that information onto the road and actual objects. Like the road in front of the driver, the designer must focus their attention on these and other factors as the technology only gets better.

1 IHS. Automotive Head-Up Display Market Goes into High Gear. IHS Pressroom. IHS, 1 July 2013. Web. 20 Dec. 2013.