at42qt1070 ATMEL Corporation, at42qt1070 Datasheet - Page 11

• Manufacturer Part Number: at42qt1070
• Description: Qtouch 7-channel Sensor Ic
• Manufacturer: ATMEL Corporation

2.8
2.9
2.9.1
2.9.2
2.10
2.11
9596A–AT42–10/10
Proximity Sensing
Types of Reset
Calibration
Guard Channel
External Reset
Soft Reset
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
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
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.
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.
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 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
on page
and a Threshold of 10 counts.
A calibrate command clears all key status bits and the overflow bit (until it is checked on
the next cycle).
“Associated Documents” on page 37
21) than the other keys. In standalone mode it should have an Averaging Factor of 16
for Cx limitations), which is extremely effective in increasing the
Section 5.9 on page
for information about design guidelines.
21) and a lower Threshold (see
AT42QT1070
Section 5.8
11