Presence detection device with a radio antenna, for a motor vehicle

A system (700) intended to be installed on a motor vehicle, comprising:

• a capacitive electrode (110;
• 310;
• 410), configured to form, with the ground, a measurement capacitor for implementing capacitive type presence detection;
• a transmitting and receiving antenna (120;
• 320;
• 420), configured to transmit and receive a radiofrequency signal in order to identify a user, the transmitting and receiving antenna (120;
• 320;
• 420) surrounding the capacitive electrode (110;
• 310;
• 410);
• an electrically conductive line (130;
• 330;
• 430), located between the capacitive electrode and the transmitting and receiving antenna, without direct physical contact with either the capacitive electrode or the transmitting and receiving antenna;
• and
• a microcontroller provided with a plurality of input and/or output ports (561, 562, 563), where each input and/or output port is able to be brought to a determined potential and/or to be used to measure a voltage signal;
• characterized in that the system (770) further comprises a reference capacitor (Cext), and in that:
• one terminal of the reference capacitor (Cext) is connected to the same first input and/or output port (562) as the capacitive electrode;
• and
• the other terminal of the reference capacitor (Cext) is connected to the same second input and/or output port (561) as the electrically conductive line;
• with the reference capacitor (Cext) and the electrically conductive line (130;
• 330;
• 430) thus defining a discharge capacitor,
• the system (700) being configured so that the measurement capacitor, formed between the capacitive electrode and the ground, can be alternately charged and discharged in the discharge capacitor, and the microcontroller notably being configured to measure a voltage representing the capacitance of the measurement capacitor.