“With more and more applications of mobile devices in automobiles, people hope that the car driving experience can be as convenient as using mobile devices, which has promoted a large number of capacitive switch backlight applications. Automotive OEM companies have found that adding backlight functions to touch switches, dials, and buttons can enhance their advantages in similar competing products and add design aesthetics to the interior of the car.
With more and more applications of mobile devices in automobiles, people hope that the car driving experience can be as convenient as using mobile devices, which has promoted a large number of capacitive switch backlight applications. Automotive OEM companies have found that adding backlight functions to touch switches, dials, and buttons can enhance their advantages in similar competing products and add design aesthetics to the interior of the car.
However, the technology of integrating the backlight into the capacitive interface is full of challenges, increasing design time and cost. Today we introduce to you 5 common challenges and their solutions.
Challenge 1: Light uniformity
The uniform lighting effect makes the appearance of the control Panel appear high-end and high-quality. In addition, the capacitive control panel may become dim due to improper placement of the LED board, or there may be fuzzy hotspots indicating the function keys, causing the user to be unable to operate the panel correctly. Therefore, the high-quality uniform lighting effect can improve the efficiency of the instrument panel, and correctly guide the user how to operate the entire process.
One way to uniformly illuminate is to support the LED from the capacitive surface to provide sufficient space for the light to diffuse across the designated area. However, this method is extremely difficult to implement when the design is restricted by space and requires ultra-thin capacitive switches.
Side-fired LEDs can be used as an effective method to provide uniform illumination. Because it is illuminated from the side instead of in the vertical direction, and a light pipe is used to redirect the light upward, the side-lit LED does not need to be separated from the designated area by a certain distance. In this way, while achieving the required light uniformity, the thickness of the capacitive switch can still be limited.
Since the brightness of the light pipe will be slightly reduced, it is important to use high-quality and high-efficiency LEDs. Moreover, the design itself will also affect the quality of the light emitted by the side-lit LED. The choice of the light pipe and its placement relative to the LED will affect the brightness.
Challenge two: light transmission
When light leaks from a capacitive button or capacitive switch to a button or switch next to it, light transmission occurs. This reduces the aesthetics of luxury car dashboards and hinders the use of switches. On the contrary, a certain space should be left between the illuminated surfaces as a transition zone between capacitive functions. But the reality is that the space of the dashboard is very limited. When the buttons and other illuminated surfaces are close together, it is very challenging to ensure that only the specified graphics are illuminated.
In automotive applications, whether the capacitive switch can be ultra-thin will be of vital importance. There are several types of side-emitting LEDs that can achieve precise lighting effects in specified patterns. However, this solution may be too costly for some design budgets. In this case, the designer of the car interior can work with the switch engineer to modify the graphics and install a smaller number of LED lights on the rear. Beads, so as to accurately illuminate the desired area.
Challenge 3: Visibility of strong light
When the outdoor light is too strong, people will feel uncomfortable when reading the smartphone screen. When using the on-board capacitive switch, the backlight will send reminders to the driver and other passengers to inform the instructions, which means that this function must be clearly visible at all times, not only at night. However, it is a daunting challenge to keep the car’s capacitive backlight still clearly visible in sufficient daylight. C During the day, the brightness of the backlight must exceed that of daylight. However, when the sun sets, it is necessary to reduce the brightness of the backlight to avoid discomfort to the eyes of the vehicle personnel and cause driving hazards.
Increasing the lumens of LED lamp beads can enhance the visibility of backlight glare. However, the greater the power of the LED, the higher the cost. In addition, the sensor needs to be integrated into the circuit to automatically adjust the brightness of the LED according to the ambient light. In order not to exceed the budget limit, other adjustments must be made in the design to offset the cost of high-lumen LEDs and increased sensors.
Challenge four: color matching
One of the leading trends in the field of automotive interiors is LED ambient lighting. For example, luminous light strips are arranged around the edges of the dashboard and central control. In order to achieve aesthetics, the backlight of buttons and switches should match the ambient lighting. However, capacitive circuits can make this color matching task very tricky.
PEDOT is a semi-transparent material that can be used as an effective material to make backlight capacitive interfaces. When using PEDOT, designers of capacitive switches should evaluate the specific colors of vehicle ambient lights, and cooperate with suppliers to purchase LEDs with accurate wavelengths to compensate for the slight color of PEDOT and color the ambient lighting match. The result is that uniform and consistent lighting can be obtained in the interior of the entire vehicle, achieving a delicate and beautiful effect.
Challenge five: tactile feedback
For safety reasons, tactile feedback is particularly suitable for in-vehicle Electronic equipment. Although only visual feedback provided by smartphones and tablets is sufficient, this poses a danger to the driver, because the driver should keep his sight on the road instead of glancing at the dashboard from time to time. Research cited in a white paper on “Frontiers in Psychology” shows that when using in-vehicle electronic devices, tactile functions have proven to shorten the reaction time and reduce the cognitive load during driving, ultimately improving driver safety.
However, to achieve tactile response and backlight functions at the same time, it will increase the number of electronic components, which will bring about space concerns for designers. Moreover, the tactile components may not be translucent, so designers may need to compensate for the LEDs, or use side-lit LEDs with light pipes, both of which will further increase the space constraints.
Flexible printed circuits (FPC) allow designers to find several ways to integrate backlighting and tactile feedback into capacitive switches at the same time. FPC is lighter and thinner than PCB, which compensates for the tactile function and the space and weight of the LED. In theory, this thin, flexible circuit can be made into a 3D shape, providing engineers with more choices, and the circuit can be installed on the dashboard, center console or armrest.
Molex has more than 40 years of rich experience in the design and manufacture of capacitive circuits, and produces millions of coils for the world’s leading automotive OEMs and customers in other industries every year. Industry-leading professional experience and excellent service complement each other, providing innovative engineering services, reliable quality, dedicated business operations and excellent customer support.
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