Five Design Challenges for Capacitive Backlight Design in Automotive Applications

With the increasing use of mobile devices in automobiles, it is expected that the driving experience of the car will be as convenient as using a mobile device, which has promoted a large increase in the backlight application of capacitive switches. Automotive OEMs are finding that adding backlighting to tactile switches, dials, and buttons can serve as an edge over the competition and add design aesthetics to a car’s interior.

With the increasing use of mobile devices in automobiles, it is expected that the driving experience of the car will be as convenient as using a mobile device, which has promoted a large increase in the backlight application of capacitive switches. Automotive OEMs are finding that adding backlighting to tactile switches, dials, and buttons can serve as an edge over the competition and add design aesthetics to a car’s interior.

However, the technology to integrate the backlight into the capacitive interface is challenging, increasing design time and cost. Today we introduce 5 common challenges and their solutions.

Challenge 1: Light Uniformity

The uniform lighting gives the control panel a high-end, high-quality look. In addition, capacitive control panels may be dimmed due to improper placement of LED boards, or vague hot spots that indicate function keys, preventing users from properly operating the panel. As a result, high-quality, uniform lighting can improve the efficiency of the instrument panel, instructing the user exactly what to do throughout the process.

One way to provide even illumination is to support the LEDs from a capacitive surface, providing ample space for the light to spread out over the entire designated area. However, this approach is extremely difficult to implement when the design is space-constrained and requires ultra-thin capacitive switches.

solution:

Side-firing LEDs can be used as an effective way to provide uniform illumination. Side-firing LEDs do not require a certain distance from the designated area due to lighting from the side rather than vertical, and the use of light pipes to redirect the light upwards. In this way, the thickness of the capacitive switch can be limited while still achieving the desired light uniformity.

Since the brightness of the light pipe will be slightly reduced, it is important to use high quality and efficient LEDs. Also, the design itself can affect the quality of light emitted by side-firing LEDs. The choice of light pipe and its placement relative to the LED can have an impact on brightness.

  Five Design Challenges for Capacitive Backlight Design in Automotive Applications

Challenge 2: Light Transmission

Transmission of light occurs when light leaks from a capacitive button or capacitive switch to an adjacent button or switch. This detracts from the aesthetics of luxury car dashboards and hinders the use of switches. Instead, there should be some space between the illuminated surfaces as a transition zone between capacitive functions. But the reality is that dashboard space is very limited, and when buttons and other illuminated surfaces are close together, it can be very challenging to ensure that only designated graphics will be illuminated.

solution:

In automotive applications, ultra-thin capacitive switches will be critical, and there are several side-firing LEDs that provide precise lighting in a given pattern. However, this solution may be too costly for some design budgets, in which case the designer of the car interior can work with the switch engineer to revise the graphics to include a smaller number of LED lights at the rear beads, thereby accurately illuminating the desired area.

Challenge 3: Bright Light Visibility

When the outdoor light is too strong, people’s eyes will feel uncomfortable when reading and looking at the smartphone screen. When using on-board capacitive switches, the backlight alerts the driver and other passengers of instructions, meaning the feature must be clearly visible all day, not just at night. However, keeping an onboard capacitive backlight clearly visible in full daylight is a formidable challenge. During the day, the backlight must be brighter than sunlight. However, when the sun goes down, the brightness of the backlight needs to be reduced to avoid driving danger due to discomfort to the eyes of the occupants of the vehicle.

solution:

Improving the lumen of the LED lamp beads can enhance the visibility of backlight glare. However, the higher the power of the LED, the higher the cost. In addition, sensors need to be integrated into the circuit to automatically adjust the brightness of the LEDs based on ambient light. To stay within budget constraints, other design tweaks must be made to offset the cost of high-lumen LEDs and increased sensors.

Challenge Four: Color Matching

A leading trend in automotive interiors is LED ambient lighting, such as the placement of illuminated light strips around the edges of the instrument panel and center console. For aesthetic purposes, the backlighting of buttons and switches should match the ambient lighting. However, capacitive circuits can make this color matching tricky.

solution:

PEDOT is a translucent material that can be used as an effective material for backlit capacitive interfaces. When using PEDOT, capacitive switch designers should evaluate the specific color of vehicle ambient lighting and work with suppliers to source wavelength-accurate LEDs to compensate for PEDOT’s slight color and color for ambient lighting match. The result is uniform lighting throughout the interior of the vehicle for a sophisticated and aesthetic effect.

Challenge Five: Haptic Feedback

For safety reasons, haptic feedback is especially suitable for in-vehicle electronics. While only visual feedback from smartphones and tablets is sufficient, it poses a hazard to drivers who should be keeping their eyes on the road rather than glancing at the dashboard every now and then. Research cited in a white paper in Frontiers in Psychology shows that haptic features have been shown to reduce reaction times when using in-vehicle electronics and reduce cognitive load while driving, ultimately improving driver safety.

However, implementing both haptic response and backlighting simultaneously increases the number of Electronic components, which creates space concerns for designers. Also, the haptic components may not be translucent, so designers may need to compensate for the LEDs, or use side-firing LEDs with light pipes, both of which further increase space constraints.

solution:

Flexible Printed Circuits (FPCs) allow designers to find several ways to simultaneously integrate backlighting and haptic feedback into capacitive switches. FPCs are lighter and thinner than PCBs, compensating for the space and weight of haptic functions and LEDs. In theory, the thin, bendable circuit could be made into a 3D shape, giving engineers more options for mounting the circuit on a dashboard, center console or armrest.

Molex has more than 40 years of experience in the design and manufacture of capacitive circuits, producing millions of coils each year for the world’s leading automotive OEMs and customers in other industries. Industry-leading expertise is complemented by outstanding service, delivering innovative engineering services, dependable quality, dedicated business operations, and exceptional customer support.

As an authorized distributor of Molex, Heilind can provide relevant service and support to the market. In addition, Heilind also supplies products from many of the world’s top manufacturers, covering 25 different component categories, and focusing on all market segments and all customers, Constantly seeking a broad product offering to cover all markets.

The Links:   CG-3202400K 7MBR35SA120

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