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Posted on 01 September 2019

Revolution in the Cockpit

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TFT liquid crystal screens and optoelectronics change passenger compartments.

So-called Central Information Displays (CID) continue to appear in more and more car dashboards. Although the CIDS are mainly used in luxury cars at the moment, experts estimate an average growth of around thirteen percent per annum in Europe over the next few years.

By Andreas Biß, Product Marketing Optoelectronics, Sharp Microelectronics Europe

 

This development is not just attributable to the equipment of luxury cars. Medium-sized and compact cars are increasingly being equipped with TFT LCDs for driver information and entertainment. Amongst other factors, this trend is being driven by technological developments that are now enabling installation of LCDs in cars for the first time and thus offering drivers real added value in comparison to traditional display instruments.

LCDs are changing interior design

The basic requirements for car LCDs are an extended temperature range of -30°C to 80°C and increased vibration resistance, in order to cope with extreme weather and road conditions. Various technologies are used to ensure consistently clear legibility under constantly changing light conditions. Sharp displays don’t just fulfil these minimum requirements for the automotive sector – the company has also developed a whole range of technologies to optimise display usage in cars. These include automotive TFT LCDs with a contrast ratio of 3000:1, which can not only be integrated seamlessly into the standard matt black dashboard areas thanks to their optimised black level, but can also ensure clear representation of the entire colour spectrum, even in bright ambient light. So-called ‘self-heating backlights’ enable a rapid cold start for liquid crystal displays at low winter temperatures and the dual directional and triple directional viewing displays developed by Sharp itself provide entirely new options for individual car infotainment for the driver and passengers.

Photointerrupter for multi-layer menu navigation

The introduction of TFT LCDs in cars has also resulted in new possibilities and requirements for the design of car interior electronics, surface feel and ergonomics. The most obvious change accompanying the introduction of CIDs is the consolidation of various switch functions into one centre control switch. In contrast to mechanical rotary and toggle switches, the multifunctional centre switches must reproduce an incredibly high number of switching states in order to navigate the multi-layer menu guides shown on the CIDs for navigation, audio, telephone, air-conditioning etc. Sharp photointerrupters make it possible to separate the mechanical design of switches from their electrical design, allowing for much greater flexibility in development, as the mechanical characteristics of the switch no longer influences the final haptic design of the operating elements. Tested in accordance with the strict specifications of AEC-Q100, the photointerrupter is used as a micro photoelectric barrier, triggered when the switch process is interrupted. Their very small size, with a side length of only a few millimetres, means that Sharp photointerrupters can be integrated without difficulty in any kind of switch. A typical centre switch has several interrupters, which cover both linear (up-down, left-right, in-out) and rotary movements. The compact dimensions of the interrupter make it possible to resolve the 360° rotation into up to 400 incremental steps, depending on application requirements.

A further advantage of the electro-mechanical disconnection is long life, since the no-contact switching process means no wear. Sharp photointerrupters are therefore a cost-effective, maintenance-free alternative to magnetic switches.

More comfort and less gasoline consumption through IR sensors

Distance measurement sensors (DMS) can also take over the function of switches for car interior electronics. In addition to comparatively low costs, the advantage of these sensors is that, as non-contact switches, they are not subject to mechanical wear and have very compact dimensions. In contrast to traditional IR sensors that calculate distance from the strength of the reflected IR rays, Sharp DMS technology is based on the rules of trigonometry. The sensors measure the distance to an object on the basis of the angle from which the reflected beam reaches the detector. The distance is therefore measured irrespective of the colour of the clothes worn by those inside the car (such as gloves) or the colour of the car interior, resulting in reliable activation of the corresponding applications. This means Sharp DMS are highly flexible for use in cars.

Example non-contact switches: they are particularly useful if you can’t see the switch. The interior lighting may, for example, be turned off simply by a wave of the hand close to the switch, without having to fumble for the switch in the dark. Sensors can also be useful for setting the seat position, by activating the Central Information Display at the time when the hand is close to the seat switches, which are often positioned where it is difficult to see them, in order to show which seat adjustment lever the hand is in contact with. It is normally difficult to distinguish between the levers under the seat.

Example automatic air-conditioning control: when integrated into the dashboard or car doors, the DMS can determine which seats are occupied and adapt the cold air requirement and air-conditioning system performance accordingly. Drivers who usually drive alone will then benefit from reduced petrol consumption. Dust sensors are a useful additional devices for automatically controlling car air-conditioning systems. They not only function as sensors to indicate when the next service is due, but also automatically ensure clean air. Sharp dust detectors register aerosol particles at a concentration as low as only 0.1 mg / m³. This high sensitivity is achieved through the use of pulsing IR signals with a pulse width of 0.32 ms. Even sporadic dust quantities can be registered reliably as peak values. For example, if you pass a construction site, the dust sensor sends a control signal that temporarily increases the performance of the ventilation and airconditioning systems. Traditional detectors based on continuous light cannot usually register such sporadic particle clouds, as the actual material quantity is too low.

Triangular measurement for higher accuracy

Brightness sensors for automatic control of display backlighting

TFT LCDs in cars not only offer new options, but also bring new requirements with them, such as automatic control of display background lighting. The correct brightness setting for the Central Information Display is heavily dependent on ambient brightness. In bright sunlight, the display needs to shine more brightly to be easily legible, while the display should be dimmed in dark light conditions. The changeover between light and dark ambient conditions sometimes occurs very quickly during driving, often when a vehicle drives into a tunnel or underground car park or because of changing weather conditions, for example. Control of the display brightness must therefore be automatic, on safety grounds at the very least. Without it, for example, the vast difference in brightness between the display and the surroundings during night driving could seriously impair the driver’s vision. Distracting reflections in the windscreen are only one consequence. By looking at an overbright display, a driver is dazzled as if by a torch. This will prevent the driver from seeing what is going on outside correctly, increasing the risk of accidents.

Taking the eye as the perfect sensor, Sharp has developed new OPIC brightness sensors that automatically adapt the LCD brightness to the ambient light. These sensors are characterised by the fact that they reproduce the brightness sensitivity of the human eye almost exactly, i.e. they mainly react within the range of visible light at wavelengths of approx. 450 to 650 nm. Integrated temperature compensation also ensures consistent operation of the sensors across the entire relevant temperature range of -40 to +85ºC for use in automotive applications. In contrast, traditional photodiodes are influenced by a significantly wider wave spectrum and the ambient temperature. They are therefore not suitable for the accurate control of display brightness.

A further crucial factor for automatic control of car LCD backlights is the rapid reaction time of the sensors, as the ambient brightness can change in a fraction of a second, e.g. when entering a tunnel. Sharp sensors require only up to 25 microseconds to adjust to new light conditions. The display background lighting can thus be altered precisely, efficiently and immediately.

The Sharp OPIC ambient light sensors are suitable for controlling the brightness of both CCFL and LED backlit displays. A microcontroller receives the OPIC sensor output signal and controls the relevant driver for the backlight. For brightness control for LED backlights, Sharp also offers LED driver ICs synchronised with the brightness sensors. These ICs work directly with the sensor signals. This means there is no need for a microprocessor to be connected in the middle.

Pulses for high sensitivity

Summary

Optoelectronic switches offer a wide range of options for implementing complex switches and automatic connections in car interiors. One of the many advantages is the separation of the mechanical and electrical switching process. This gives car interior developers more freedom when it comes to the surface feel of switch design. To a certain extent, sensors can entirely replace classic switches and function as non-contact ‘switches’. This makes it possible to automate individual applications such as the control of display brightness and air-conditioning and thereby increase their efficiency. Sensors therefore contribute directly to lowering fuel consumption. Thanks to the separation of the mechanical and electrical switching process, optoelectronic switch elements are not subject to wear, unlike traditional toggle and rotary switches. They are also much cheaper than magnetic switches – a major advantage, particularly for the price-sensitive automotive industry.

 

 

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