Redefining automotive HMIs using advanced optoelectronics

4 min read

There are a vast number of multimedia, communication, air conditioning, telematics and navigation utilities now being built into in the average car. All of these, of course, need efficient control mechanisms. Automobile manufacturers have, in recent years, placed far greater importance on the implementation of highly intuitive human machine interfaces (HMIs) that can address the expanding scope of functionality that drivers need to deal with, while ensuring that they are still able to concentrate fully on the road ahead. As a result interest is growing in HMIs that are capable of supporting touch-less operation.

Given the multitude of control functions currently being incorporated, conventional approaches to HMI design have now become outdated and this is what is driving car manufacturers to make further investment. Industry analyst TechNavio has predicted the automotive HMI market will rise at a compound annual growth rate of 7.7% over the next four years as a result.

For an automotive HMI to be effective, it needs to allow tasks to be undertaken in a straightforward and prompt manner – as the longer timeframe and greater the level of concentration that it calls for, the more it effects the user's driving ability. If the dashboard is packed with different switches and buttons, without a well-organized structure, then it could potentially make things difficult for the driver when trying to operate different systems. On top of this, it may mean that the vehicle's interior is less visually appealing. Innovative optoelectronics offers the possibility to implement multi-mode HMI systems, where the detection of light can supplement the touch control element. There are, however, technical challenges associated with this approach that need to be overcome.

To ensure that operational integrity is maintained, the image sensing technology used in the touch-less component of a HMI mechanism needs to have the following characteristics for it to be located in an automotive environment. Firstly it has to offer strong sunlight robustness, due to the broad variation in background light levels that can be witnessed. In addition, its ability to cope with electro-magnetic interference (EMI) must be adequate. Compactness, integration aesthetics and cost effectiveness also need to be factored into the equation.

Through analysis of the light reflected from a target object, various gestures (like left/right or up/down swipes) can be identified and subsequently acted upon. Numerous tasks may thus be carried out while keeping both cognitive and visual distraction to a minimum, as the inconvenience of touch is not required for them. This presents a more elegant methodology which allows the cabin's aesthetically qualities to not be impacted upon. Such touch-less input interfaces are suitable for stand-alone use or they can work in conjunction with buttons, touch screens and voice recognition systems, depending on the task or the user's preferences. Furthermore, reliance on some form of voice recognition is avoided (which would have to contend with cabin background noise, poor annunciation, regional accents and such like) that can result in errors occurring through misinterpretation.

In addition to this, use of 3D sensing technology is becoming an area of great interest to automotive engineers, and is likely to have an important part to play in the future of automobile HMI development. Optical time-of-flight (ToF) has shown itself to be a highly effective means by which to compile 3D imaging data on the user's hand position, thereby allowing relatively complex gesture recognition. In a ToF sensing system an emitter casts an infrared beam which will be reflected back to the sensor element by any objects present within the scene. The sensor is then able to compare the reflected signal with a reference signal and determine the phase shift caused by traversing that path. From this a precise calculation can be made of the distance to the object and a detailed 3D image constructed. Such technology has already proved extremely popular in relation to enabling more immersive video gaming experiences. With regard to automotive implementation, it could potentially go far beyond the determining of hand positions, by allowing acquisition of information about the driver's head and body position/orientation. This could then be fed back to the vehicle's driver assistance apparatus in order to judge the driver's state of awareness at that time and (should the need arise) perform an automated reaction to a perceived danger.

Though ToF is already being applied within the latest gaming systems, it must be noted that implementation here is fairly easy to accomplish as the operating environment is normally very stable and almost certainly benign. Placing ToF into an automotive context is a very different prospect. Once again the influence of sunlight variation must be considered. Through the introduction of multi-pixel image sensing devices, which support high dynamic range (HDR) operation, these difficulties can now be circumvented however.

Using its expertise optoelectronic technology and automotive applications, Melexis is making major steps in the deployment of touch-less HMI mechanisms that will complement touch-based controls. Its MLX75030 and MLX75031 ActiveLight ICs sensor enable accurate proximity and gesture detection while still having the necessary sunlight robustness, thanks to proprietary integrated ambient light suppression technology. For each of these ICs there are four independent, simultaneously operating light measurement channels – two of which are concerned with addressing ambient light and the other two for taking care of detecting active optical reflection from the target object (for example, the driver/passenger's hand) via logarithmic current sensing photodiodes. In addition to the ambient light suppression, an integrated temperature sensor is employed to compensate for the influence of temperature on the ambient light channel. Digital data on the active light and ambient light levels is generated through the 16bit data converter which is embedded into each IC. This is then passed to an MCU for processing. Sophisticated algorithms are then used to differentiate various gestures. The driver/passenger discrimination function means that infotainment options that are considered to be seriously distracting to the driver can only be accessed by the passenger. As it is just the LEDs and accompanying photodiodes that need housing on the dashboard surface (while all the supporting electronics can simply be accommodated in any available space behind this), the system does not impinge in any way on the vehicle's interior design.

Melexis is also helping to migrate ToF technology to automotive industry use. It has developed multi-pixel HDR image sensing devices that have sensitivity levels enabling data capture with a depth accuracy of 1 to 2%. The company's MLX75023 QVGA resolution ToF sensing device has a 600frame/s raw frame rate. It has a spectral response range of 800nm to 900nm and, when working in combination with an appropriate modulated infrared emitter, delivers detailed real-time 3D imaging data. Each of the MLX75023's pixels can cope with as much as 120kLux of incident background light, giving it more than ample capacity to address any variations witnessed.

Thanks to resilience to the effects of ambient light variations and the presence of EMI, it is now possible to serve the automobile industry with more sophisticated, optically-based HMI technology. These new easy-to-use, almost distraction-free HMI mechanisms will support the control of different functions without being reliant on physical touch, keeping the safety of vehicle occupants (and other road users) as a priority.

Author profiles
Kristof Lieben is an application engineer and Gaetan Koers is a product line manager. Both are with Melexis.