Datasheet

11
9596A–AT42–10/10
AT42QT1070
2.8 Proximity Sensing
The QT1070 is capable of detecting near-proximity or touch. By increasing the sensitivity, the
QT1070 can be used as a very effective proximity sensor, allowing the presence of a nearby
object to be detected.
As the object being sensed is typically a hand, very large electrode sizes can be used (see
Section 2.12.3 on page 12 for Cx limitations), which is extremely effective in increasing the
sensitivity of the detector. Note that, although this affects the responsiveness of the sensor, it is
less of an issue in proximity sensing applications; in such applications it is only necessary to
detect the presence of a large object, rather than a small, precise touch.
Proximity sensing technology enables users to interact with consumer electronics without even
touching them. With this powerful technology, sensors in a device such as a PC notebook, PC
peripheral, or digital photo frame, sense the presence of a user’s hand and take action. These
sensors can illuminate LEDs for discoverable buttons, wake devices from power-saving mode
immediately, or activate other functionality.
Refer to “Associated Documents” on page 37 for information about design guidelines.
2.9 Types of Reset
2.9.1 External Reset
An external reset logic line can be used if desired, fed into the RESET
pin. However, under most
conditions it is acceptable to tie RESET
to Vdd.
2.9.2 Soft Reset
The host can cause a device reset by writing a nonzero value to the RESET
byte. This soft reset
triggers the internal watchdog timer on a 125 ms interval. After 125 ms the device resets and
wakes again.
The device NACKs any attempts to communicate with it during the first 30 ms of its initialization
period.
2.10 Calibration
Writing a nonzero value to the calibration byte can force a recalibration at any time. This can be
useful to clear out a stuck key condition after a prolonged period of uninterrupted detection.
Note: A calibrate command clears all key status bits and the overflow bit (until it is checked on
the next cycle).
2.11 Guard Channel
A guard channel to help prevent false detection is available in both modes. This is fixed on key 0
for standalone mode and programmable for comms mode.
Guard channel keys should be more sensitive than the other keys (physically bigger). Because
the guard channel key is physically bigger it becomes more susceptible to noise so it has a
higher Averaging Factor (see Section 5.9 on page 21) and a lower Threshold (see Section 5.8
on page 21) than the other keys. In standalone mode it should have an Averaging Factor of 16
and a Threshold of 10 counts.