qt1060 Quantum Research Group, qt1060 Datasheet - Page 8

• Manufacturer Part Number: qt1060
• Description: Qtouch? 6-channel Sensor Ic
• Manufacturer: Quantum Research Group

2.9
2.10
2.11
2.11.1
8
Calibration
Guard Channel
Signal Processing
AT42QT1060
Detect Threshold
The command byte can force a recalibration at any time by writing a nonzero value to the
calibration byte. This can be useful to clear out a stuck key condition after a prolonged period of
uninterrupted detection.
When the device recalibrates, it also autosenses which keys are enabled by examining the burst
length of each electrode. If the burst length is either too short (if there is a missing or open Cs
capacitor) or too long (a Cs capacitor is shorted), the key is ignored until the next calibration.
The count of the number of currently enabled keys is found in the status response byte. This
number can change after a CAL command; for example, if a Cs capacitor is intermittent.
The device has a guard channel option, which allows any key, or combination of keys, to be
configured as a guard channel to help prevent false detection. Guard channel keys should be
more sensitive than the other keys (physically bigger or larger Cs), subject to burst length
limitations (see
With guard channel enabled, the designated key(s) is connected to a sensor pad which detects
the presence of touch and overrides any output from the other keys using the chip’s AKS
feature. The guard channel option is enabled by an I
To enable a guard channel the relevant key should be removed from the key mask (see
1 on page
other keys for the guard function to operate. Note that a detection on the guard channel does not
cause a change request.
With the guard channel not enabled, all the keys work normally.
Figure 2-1.
The device detects a touch when the signal has crossed a threshold level and remained there
for a specified number of counts (see
key-by-key basis using the key threshold I
14). In addition, the guard channel needs to be included within the AKS mask with the
Guard Channel Example
Section
2.11.3).
Section 5.11 on page
2
C-compatible commands.
2
C-compatible command.
Guard channel
17). This can be altered on a
9505D–AT42–12/08
Table 5-