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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?

A gesture of (top bottom) is similar to the up/down action of a button press. However, when an up/down button is held pressed, the screen keeps scrolling up/down as long as the button is held pressed. In other words, the actions 'sticks' as long as the button is pressed. To replace this button action completely with a gesture, the gesture needs to be able to support this 'sticky' feature too. We will modify the gesture as described below to accommodate this. When the hand moves from the top sensor and down towards the bottom sensor, the system decodes this as a (top bottom) gesture as soon as the hand moves past the bottom sensor.

We can modify the gesture so that the scroll down command is sent as soon as the hand reaches the last sensor in the gesture sequence; in this case, the bottom sensor. Furthermore, the command is issued repeatedly as long as the hand remains present over the bottom sensor. When the menu item required is reached, the hand moves further down and away from the bottom sensor and the issuing of scroll down command is stopped. So to make a 'sticky' gesture, instead of moving the hand away from the system in one go, we stop the hand on the last sensor just before moving out of the range of that senor. The command is issued as long as the hand stays over the sensor.

A rawcounts plot for top and bottom sensors for this sticky (top bottom) gesture is shown in figure 5. The bottom sensor continues to stay triggered for more time after the top sensor stops sensing the hand. This indicates that the hand has stopped at the bottom sensor instead of continuing straight down. To issue the sticky command, we check if the top sensor was triggered first, followed by triggering of the bottom sensor. Then the top sensor no longer senses a hand while the bottom sensor still continues to sense a hand near it. After the hand stays near the bottom sensor for more than a threshold of time, the sticky command is issued as long as the bottom sensor senses the hand near it. Similarly, other gestures too can be modified to have 'sticky' feature. This enables gestures to replace the up/down button functions completely.

Figure 5: Signal plot for top and bottom sensors for sticky (top bottom) gesture. The signal on the bottom sensor stays on, longer indicating a 'sticky' gesture.

The hand can start over any of the sensors and then traverse in a circular pattern in either a clockwise or anticlockwise direction over the other sensors. The loop is completed when the hand reaches the sensor on which it started then exits the circular loop gesture by moving away. For example, the hand can move over the right sensor and then move clockwise over the bottom, left and top sensors in that order before exiting the loop over the right sensor again. Similarly, a counterclockwise loop can be completed by reversing the direction of movement of the hand. Also, multiple rotations can be counted from the sensor excitation order.

The circle gesture is similar to the action of 'turning a knob'. This can be associated with commands like volume up and down for the music player menu or zoom in and zoom out for browsing maps.

In this article, we have discussed the detection of simple proximity hand gestures using capacitive proximity sensors. Using these same principles, we can build more complex gestures which may involve using both hands to draw a pattern in air. The success of detection of such gestures, however, still depends on how good a sensor pattern we choose. It is important to choose a suitable pattern which allows for tolerance in hand movements while drawing gestures and yet have a clear distinction in the order in which the sensors are triggered.

About the author
Sivaguru Noopuran is a Senior Product Marketing Engineer for automotive products at Cypress Semiconductor Corp., with more than seven years of experience. His primary interests include user interface solutions and product management.

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