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Implementing proximity gesture for automotive HMI

Posted: 10 Feb 2016 ?? ?Print Version ?Bookmark and Share

Keywords:Capacitive proximity sensors? gesture recognition? infotainment? rawcounts? capacitance?

Capacitive proximity sensors are generally utilised for detecting the presence of a user within proximity of the sensors. Upon detection, we can choose to make backlights glow to bring focus on a specific button or bring a system out of low power operation after having sensed the user's presence. Specifically in automotive applications, capacitive proximity sensors are used to sense a user and turn on the cabin lights or activate the keyless door unlocking system. In addition to sensing the presence of a user near the sensor, we can use multiple proximity sensors placed suitably to recognise simple hand gestures in the air. The data from all sensors can be combined together to map movement of a users hand in the proximity area of sensors. These gestures can be used as a way to provide inputs to a system such as to control the media player, navigate a map, or browse a playlist.

We can place multiple proximity sensors in a suitable pattern spatially apart from one other. As a hand moves across the sensors, the time instants at which it is detected by each of the sensors will be different. The relative order of detection of the hand and the time duration between detection by different sensors can be used to estimate the direction and pace of movement of hand. Gestures can be as simple as drawing a straight line in the air by moving the hand from left to right over the sensors, or a complex one involving drawing patterns such as a circle in air. In this article, we will see how to implement simple gesture recognition and how more complicated gestures can be implemented using multiple sensors in different patterns.

Consider four capacitive proximity sensors arranged as shown in figure 1 around the infotainment system of a car.

Figure 1: Capacitive proximity sensors placed around infotainment system on the right picture and the sensors with their position labelled on the left picture.

Placement of the sensors needs to be chosen such that there is a difference in the order in which sensors are triggered when the hand makes a gesture over the sensor plane. We identify the order in which sensors are triggered by hand movements. If the order matches any of the preset sequences, then the corresponding gesture is issued. We will use the sensor placement pattern shown in figure 1 as a reference for explaining the gestures discussed in this article.

Consider a simple gesture of a hand drawing a straight line in air by moving from left to right over the sensors as shown in figure 2(a). When hand moves from left to right over the sensors, the left sensor will be triggered first as soon as the hand approaches the system. Here the term 'triggered' is used to mean that the sensor has detected an object in its presence; this is not to be mistaken for enabling the proximity sensor. The proximity sensors are enabled as soon as the system is turned on and they keep scanning for objects in their proximity.

Figure 2: (Top) Left to right hand movement gesture drawing a straight line in air. (Bottom) Plot of signal for each of the sensors as hand draws the straight line gesture

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