Use of a proximity sensor to wake up the capacitive controller from standby mode. This
method is similar to the ganged sensor mode but involves using a
capacitive proximity sensor instead of the virtual ganged sensor.
A capacitive proximity sensor is a loop of copper trace on a PCB or a
loop of wire connected to the capacitive sensing controller. This
capacitive proximity sensor can detect the presence of a hand when the
hand is near the sensor without it actually touching the sensor.
Unlike all the other methods discussed before, which actually require a
sensor to be touched, this method doesn't require any physical touch to
wake the system up. A capacitive proximity sensor is integrated into the
user interface panel such that it enables the system to wake up when a
user's hand approaches the user interface panel. A simple construction
is show in Figure 1 below.
Figure 1: Capacitive buttons with capacitive proximity sensor
the standby mode, only the proximity sensor is scanned. Scanning only
the proximity sensor reduces the total scan time thereby reducing the
average power consumption. When the user's hand approaches the user
interface panel, the proximity sensor detects the presence of the hand
and wakes up the capacitive controller. Once woken up from its standby
mode, the capacitive controller moves to active mode and scans all the
button sensors to detect the touches.
A value addition would be to control the backlight on user interface
panels using the proximity sensor. Whenever a capacitive controller is
in standby mode, the backlight can be turned off to indicate the
inactive mode of the equipment. Once a user's hand approaches the panel
and the proximity sensor detects the same, the backlight can be turned
on aiding the user in touching the correct buttons. This also helps
reduce the overall power consumed by the end system. This is known as
wake on approach.