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Over the next few years, graphics-driven instrument-cluster and center-stack displays will migrate from high-end into mid-market automobiles. Luxury vehicles will continue their irresistible push toward PC-level graphics, 3D animation, and video. But, there is a market demand to enrich the driving experience across lower-cost vehicles with infotainment, at-your-fingertips information, and increased safety.
Sophisticated graphics will play a bigger role in making driving safer and more enjoyable. But for automotive electronics design engineers, this market shift requires the acquisition of new design disciplines—and a new set of decisions on how to best implement them.
While the basic graphics technology has already been developed by PC and consumer electronics design engineers, automotive engineers must find ways to make them work inside a car. Elevated operating temperatures, severe electro-magnetic interference (EMI), tight space constraints, aggressive power consumption goals, and much higher standards of reliability all make in-vehicle designs uniquely challenging.
Feature sets
Today's mid-market automobiles have largely begun to reduce the amount of electro-mechanical gauges with an increase in the amount of information displayed digitally such as fuel level, odometer readings, and warning lights. They are, however, mainly still monochrome and modest in size (below).
In the center-stack panel, radio pre-sets and other entertainment oriented features may have a digital read out. The same is true for heating and air conditioning settings. The prevalent display technology is still segmented and dot-matrix LCDs with limited graphical content.
By 2009, such displays will have changed significantly. Mid-market vehicles will begin adopting some of the features now seen in higher end vehicles, including full-color TFTs with enhanced graphical driver information content. These data may include information such as distance-to-empty, outside temperature, elapsed trip time, etc.
Several features that appear in some current vehicles are poised to become much more common. For example, by law, tire pressure information will become universal, and digital readouts providing turn-by-turn directions and navigation will become more commonplace. A camera embedded in the rear of the car will provide the driver with a video image in the instrument panel to assist with parking. In some higher-end systems, the speedometer "pointer" will be drawn graphically replacing today's traditional mechanical stepper motors.
Display technology improvements will increase driver information and content readily available in next generation instrument cluster systems and use graphically presented, rather than mechanical, pointers.
Animated graphics will be used in new and interesting ways. When a driver enters the vehicle, for instance, scrolling text might begin with a spinning logo of the carmaker and may be followed by some automobile diagnostic information (fuel level, temperature, even a traffic report for GPS equipped vehicles, etc).
When the car is taken into the shop for maintenance, the same screen could display much more detailed diagnostics to the mechanic. Once the car is on the road, safety information such as lane-departure or road hazard warning will be graphically displayed. These enhanced graphical features are facilitated by the adoption of the color TFT in dashboard applications.
Driving the display, managing the power
In today's automobiles, a microcontroller (MCU) controls a digital readout system by communicating with a basic chip-on-glass graphics controller that sends the timing signals to the display. The MCU must synchronize the signals to assure that the display has a continuous visual effect. The MCU also has to interface with memory and the CAN network.
Adding more displays increases the timing complexity, the number of connections, and both the number and the proximity of traces on the printed-circuit board (PCB) in the electronic control unit (ECU).
This creates new design considerations that involve interference and power management. EMI becomes more likely, especially in the cockpit area. Designing the PCB to minimize this interference requires additional expertise.
Similarly, as the complexity of the instrumentation cluster rises, more attention must be paid to power management because the control panel is one of the few systems in a vehicle that remains on after the engine is turned off, with only the battery available for power. Power drain for the instrument cluster may also begin before the engine is started. Typically, when the car door is opened, the instrument cluster is activated to show diagnostics and status information.
The MCU plays an important role in power management. The choice of MCU is key to achieving an acceptable level of performance both in terms of its operating current and in its ability to wake up the system via interrupt when the car door is opened or upon ignition start.
The decision to use a color display sets off a series of design considerations—the first of which concerns the requirement of a graphic display controller. Basic questions include: graphics resolution, color depth, memory management, and, perhaps most important, how are the graphics generated? Basic chip-on-glass controllers may not provide sufficient performance.
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