The Magic of InPlane Sensing for Automotive

October 21, 2022

What is InPlane

In the automobile, the surface is defined as the any material in an XY direction. This could be the dash, center console, interior door, headliner steering wheel surface. The cross-sectional thickness is the Z direction. And from a sensing perspective, this is referred to as the stack thickness. The side of the surface that the user touches is often referred to as the A-Surface, and in a sheet of plastic the A-Surface with a thickness, in this example of 2mm would be the stack thickness.

InPlane sensing is the ability to provide sensing input in the thinnest total depth physically possible, in the same plane as that A-surface so the sensor board is in the plane of the A-Surface.

Today’s Sensor Module

Today’s sensor module needs to support the sensing layer and the controller circuitry. In delivering the HMI (Human Machine Interface) experience there is also feedback than can include several types of feedback such as lighting, audio, and haptic, or if a mechanical mechanism mechanical feedback such as from a tact switch.

In automotive lighting applications using traditional lighting methods there is a light pipe framework and the LED blasts light at a distance through the light pipe to achieve the specified brightness to back light a given icon. Intelligent illumination not only lights the touchpoint to inform what function is enabled but when engaged it would show a different color to show it’s engaged.

For example:

  • Non-Illuminated = a hidden/ unavailable touchpoint,
  • White light = available illuminated touchpoint (ex. Headlight white icon, light is off)
  • Green light = enabled function (ex. Headlight green icon, headlights are on)
  • Blue light = secondary function (ex high beam headlight blue icon, high beam light is on)

To understand how to enable all these functions with one touchpoint engagement refer to gestures blog. The user experience and final behaviors tie to certain standards and are under the control of the OEM, they are dependent on the selected HMI design components capabilities and the imagination of the interface designer. Some may only need white to identify the button and not opt to provide feedback of current state. If there are multiple touchpoints there may be a need to individually address each touch point and its respective function separately. Not all in-market technologies / solutions can offer individually addressable capabilities.

Figure 1: Example Traditional HMI Module Stack

The traditional module has several functional components

  1. sensing controller (ex. Capacitive controller, feedback controller for lighting,
  2. processing controller to control the sensors and feedback mechanisms
  3. feedback controller PWM (Pulse Width Modulator) components for
    • lighting effects such as dimming or effect patterns),
    • audio speaker components (for example in a steering wheel), and
    • haptic controller and haptic motor if a solid state component, and
  4. the communications board to support connectivity to the rest of the car through common protocols such as LIN or CAN.

For example, with a capacitive technology there is a sensing layer, using materials such as ITO (Indium Tin Oxide) film, FPC Flexible Printed Circuit, or PCB (Printed Circuit Board) that delivers the capacitive trace that laminates to the A-surface and connects to the sensor silicon which is part of a module with supporting electronic components.

Today the most common automotive application is this sensing film layer has been laminated to the back of the A-surface and in a few cases inserted InMold, literally in the molded part.

IME, In Mold Electronics is one form of InPlane, where not just the film but the entire sensing electronics components including the controller are in the molded part.

The InPlane value proposition is that it brings is amazing in many areas and now can offer that in the plane of the A-surface

Take one sample existing module, the exact module and manufacturer is not relevant, likewise the exact measured numbers are relative and will vary for each part, but in this teardown analysis of the production HMI part assembly, the thin-ness comparison to InPlane can’t be overlooked.  Reductions in the amount of plastic that results in Sustainability and Recyclability advantage.  The total space, the volume cavity is drastically reduced that enables designers to create interacts where previously prohibited.

Imagine a center console stowage cover, InPlane could fit where a traditional assembly could not even consider fitting enabling new application that were previously not an option.  When implemented throughout the vehicle, just like in automotive wiring, a network protocol delivers drastic weight savings, like the transition to networked wiring, this offers the same weight savings that adds up to increasing driving range, which ultimately is a measure that hits the bottom line for car buyers.

InPlane is a single planar thin module that can also be the surface for the other desired components beyond sensing such as an MCU, feedback that could include lighting, speaker or haptic motors and the communications board.

InPlane Sensing HMI is the ability to offer all the components the primary sensing, processing, feedback, communications all “in plane.”

Reimagine with InPlane

Now reimagine that what has been done in the past with todays advanced technology capabilities. OEMs can rethink the way of the past and get the same benefits in less space. With integration of the key components that can be integrated into one tiny component(s) this is now becoming a reality.  InPlane Sensing and InPlane HMI (sensing plus integrated control, processing, feedback, and communications) is the method for OEM (and Tier1s) to deliver this new experience.

Figure 2: Example InPlane HMI Module Stack

In the above figure the “USS Module” is the one InPlane sensing component and it laminates (though one of several methods to the OEM/Tier1s preference) and there’s an optional protective back that encases the module. Note this USS module is an extremely durable component that can also fit into other technologies such as InMold where the electronic component(s) are molded into the A-Surface.


Manufacturing with fewer parts, and fewer complexities is a significant advantage, all relating to cost reductions and when using solid-state components compared to mechanical switches and multiple parts result in higher reliability, pleasing design aesthetics.

Supply Chain

The approach of manufacturing from a series of discrete components mentioned earlier also introduces the Supply Chain issue, that is that the assembly is not complete till all the discrete parts are available. It only takes one delayed part to stop production.

In comparison if there were only one component that could replace a set of discrete components then there are vast supply chain benefits, provided the part had high availability. Production time is also simplified because there are fewer components to assembly, and if the part offered optionality, the configurability to meet varying needs, one part for good, better, best offerings, it simplifies manufacturing.

The Merit of Truth

It all starts with great sensing. It’s the starting point that drives and enables good orchestration of the feedback effects, particularly necessary for great haptic feedback in solid-state designs. Great sensing is measured in accuracy, the goal to strive to hit 100% accuracy of intended touch and rejection of unintended touch. (See blog on the “Merit of Truth” Explained for more information.)

The most basic or common sensing is using a sensing technology such as capacitive. Many know there are challenges with using only one sensing technology as “the merit of truth.” the challenges with things like capacitive technology, in that its accuracy can be challenged with specific scenarios, sometimes called corner cases such as wearing gloves, or interactions with liquids like water drops can impact its sensing accuracy. There are several approaches to improved accuracy, two common approaches are multi-mode sensing, and algorithm logic (the highest forms are Artificial Intelligence, that include Machine Learning Algorithms). Using the appropriate approach is a function of the challenges that need to be solved and the effort and desire to achieve a given level of accuracy in both properly detecting an intended interaction and rejecting in advertent actions.

Closely tied to accurately sensing touch, the next dimension has several names, from accidental activation, false triggers, un-intended touch. These inadvertent actions manifest themselves in many ways but accidental activation avoidance is another critical measure that enhances the touch sensor’s score.

Multi-Mode Sensing

Multi-Mode for sensing is like the name implies uses several modes of sensing, sometimes described as “sensor fusion.” Traditionally the components of sensor fusion include multiple types of sensors, a Dual-Mode sensor uses two forms of sensing together.

Figure 3: Examples of DualMode sensing

To include two forms of sensing it must be integrated in a processor with algorithms. Obviously the better faster the processing the better, but the need is to ensure zero latency. When shifting processing to a shared host could and often introduces latency. Note our measure of latency is not the best case, but the worst case, the scenarios of the processor under normal full use, and there should not be latency for good usability performance. The other way to resolve is to have dedicated local processing so it’s just focused on the HMI needs and isn’t bogged down with other tasks. (We will introduce more details on the topic of Zero Latency)

InPlane meets UltraSense SmartSurface HMI

The InPlane challenge is to find and assemble the right components to make it all happen. The UltraSense SmartSurface HMI is an excellent choice because its one tiny silicon component that is the size of the date printed on a penny, and it can deliver it all-in-one control capabilities.

Figure 4: USS TouchPoint Z HMI Controller

Rapid Prototype Development

When developing prototypes, depending on your companies’ capabilities, the SSI is ready to roll, inset into opening and connect to get started fast.

Figure 5: USS Solid State Interface
Figure 6: USS Sample TouchPoint Bar Module

This is one of many modules available and has the capabilities with the component configuration*:

Sensing TPZ HMI controller, in CapForce Mode with Cap Sensing Layer,

Processing and Algorithms in TPZ controller

  • 1st and 2nd Order algorithms for increased touch accuracy and elimination of accidental touch events
  • Fix-In-Post tuning for better systems experience design

Feedback control:

  • LED Illumination with PWM effects to attenuate and dim, as well as heartbeat and other effects,
  • Audio control that can drive an additional internally located speaker or connect to a network addressable audio system,
  • Haptics control that includes the driver to process custom pattern waveforms and with the ability to connect a haptic motor

Communications control: LIN protocol along with standard GPIO

*Note exact features are module specific and subject to change per module design

USS Modules exist to help rapid prototype solutions and are intended to laminate to the backside of the A-Surface.

InPlane Essential Requirements:

The key ingredients checklist to enable InPlane technology:

  • Multi-Mode InPlane Sensing (Sensor Fusion)
  • ML Algorithms for increased accuracy, and Fix-In-Post capability to enhance and tune design after the design prototype is built
  • UX Design Tool (home grown or off the shelf) that can tune the experience, in the assembly, in the component (like in the steering wheel), and fully installed in the vehicle prototype
  • Edge Processing to ensure low latency feedback, essential for experience based controls such as haptic feedback performance
  • HMI Controller or a DiY controller board to combine all the key aspects in one InPlane module.

Note: The more components the higher the supply chain risk, the higher the coordination with multiple drivers and maintenance updates, an all-in-one solution helps deliver the full experience with one part.

  • Optionality: which is the ability build one part and enable options via firmware/software settings. This simplifies manufacturing, supply chain and can reduce part numbers yet can easily be configured to support a good / better / best type of offering, and enabled at the factory build, at the dealership, or after sale through Over-The-Air (OTA) updates.
  • Product development options include options of  USS Solid State interfaces (SSI), or use existing HMI modules that help speed up prototyping, or develop custom HMI boards for serial production.

For select applications, the option to select an existing readily available SSI design could be the fastest prototyping method for creating the opening in the A-surface for adhering the SSI. SSI applications are pre-calibrated and ready to roll.  SSI solutions are available in all shapes and sizes, including solutions for door, eLid and more.

Contact USS for more information

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