Capacitive proximity sensors are generally used to detect 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 recognize 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