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Capacitive touch application: Automotive door handle

Posted: 18 Apr 2016 ?? ?Print Version ?Bookmark and Share

Keywords:touchscreens? door handle detection system? capacitive detection? rotary knobs?

Centre stack touchscreens in the dash are becoming quite typical; invisible touch buttons are replacing mechanical buttons; and touchpads are bringing new functions to rotary knobs (figure 1). Electronic pedals can even open trunks with the approach of the owner's foot, and doors can unlock without any action from the driver. This last function is one of the toughest to implement. The door handle detection system needs to be miniaturized, consume almost no power, be fully reliable and immune to all disturbances, and be transparent to the user. For all these reasons, capacitive detection in door handle applications is more and more a field requiring research and innovation.

Figure 1: The many applications of capacitive touch and sensing in automobiles.

Figure 1 shows some of the many applications of capacitive touch and sensing in automobiles. In the door handle application, patented Atmel charge transfer technology coupled with Atmel automotive microcontrollers (MCUs) has already resulted in various applications of the first generation of Atmel QTouch software library solutions.

Atmel is now bringing to the market a new generation of capacitive touch solutions, based on a combined hardware and software approach, particularly the combination of a hardware Peripheral Touch Controller (PTC) and a software library (the QTouch library). Applied in the door handle domain, it is touted to fulfil the most demanding requirements.

Introduction to the door handle capacitive detection
The door handle is part of a Passive Entry/Passive Start system. This complex system is mixing LF (e.g. an ATA5291 LF antenna driver and an ATA5702 key fob controller) and HF (e.g. an ATA5831 HF transceiver) communications, data encryption (e.g. AES), securitized protocols (e.g. Atmel Open Immobilizer Protocol), and algorithms for geo-localisation. All these complex functions consume power and need to be activated when the driver is ready to open the door. The capacitive detection in the door handle module is a key feature of the system. In order to detect the hand just before the driver is pulling the door handle, the touch system has to detect the palm and wake up the whole system in advance to allow enough time for a complete secure communication and authentication. In other words, this all has to happen effectively before the driver pulls the door handle so that it opens as if it was never locked. As the driver leaves the car, a similar function locks the door, usually with a specific gesture on the door handle (a simple touch with the thumb for instance).

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