Capacitive sensing – ushering in a revolution in automotive HMI design

March 17, 2011 // By Prem Kumar Arora, Manu Verma
With the increase in the amount of information interchange between a human being and various systems in a car, Human Machine Interface (HMI) technologies have gone through a paradigm shift. This article highlights the importance of capacitive sensing in the evolution of Human Machine Interface from simple mechanical buttons to present day advanced systems. Topics covered in this article include introduction to capacitive HMI technology, change in design methodologies and some of the applications which have evolved because of capacitive touch sensing.

The increasing numbers of electronic systems in a car have ushered in a revolution which has transformed the car into a safe, luxurious and intelligent machine. One thing that has not changed however is the importance of human interaction with the car. This interaction defines the user experience and is a key marketing differentiator between different vehicles.

The systems measuring and tracking interactions of the user as well as providing feedback are collectively known as Automotive Human Machine Interface (HMI) systems. From the user's perspective, this interaction maybe conscious - when he deliberately provides input to a system, or subconscious – when the system measures his intent without his knowledge.

Even with the inherent barriers in the adoption of new HMI technologies in the automotive environment, engineers are constantly trying to improve HMI systems to make them more intuitive, look cooler, and be more accurate. At the heart of this change are innovative human interaction sensing technologies which are enabling this evolution. One such technology is capacitive sensing which has revolutionized the design and implementation of HMI applications.

Very simply, a capacitive sensor is composed of a pair of adjacent electrodes.

When a human being (or any other conductive object) comes in proximity to these electrodes, there is additional capacitance between the electrodes and the object which can be measured to detect the object's presence.

Figure 1. Capacitive Sensors

Using this technology, it is easy to build touch sensors acting as buttons, sliders, trackpads etc.

Alternately capacitive sensing can also be used for proximity sensing where no contact is required between the sensor and the user's body. This can be achieved by increasing the sensitivity of the sensors. Further, such sensors are non -line of sight, therefore, a single sensor is enough to detect approach in 3 dimensions.

Such a technology becomes even more powerful in conjunction with programmable mixed signal controllers. Such devices enable the measurement of capacitance

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