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Número de pieza QT60161B
Descripción 16 KEY QMATRIX KEYPANEL SENSOR IC
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QT60161B datasheet

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QT60161B pdf
©Quantum Research Group Ltd.
Figure 1-5 Circuit Block Diagram
The threshold is user-programmed using the setup process
described in Section 5 on a per-key basis.
Vcc
Opt A Opt B
QT60161
LED
Scope
Sync
Reset
X0
X1
X2
X3
Wake /
Sync
CS0A
CS0B
SPI
to Host CS1A
UART
to Host CS1B
CS2A
CS2B
Sample caps
CS0
CS1
CS2
CS3A
CS3B
CS3
VREF
Sample
Y0 Y1 Y2 Y3
X0
X1
X2
X3
2.3 Hysteresis
See also command ^C and ^D, page 21
Refer to Figure 1-6. The QT60161B employs programmable
hysteresis levels of 12.5%, 25%, or 50% of the delta between
the reference and threshold levels. There are different
hysteresis settings for positive and negative thresholds which
can be set by the user. The percentage refers to the distance
between the reference level and the threshold at which the
detection will drop out. A percentage of 12.5% is less
hysteresis than 25%, and the 12.5% hysteresis point is closer
to the threshold level than to the reference level.
The hysteresis levels are set for all keys only; it is not
possible to set the hysteresis differently from key to key on
either the positive or negative hysteresis levels.
2.4 Drift Compensation
See also commands ^H, ^I, page 22
Signal levels can drift because of changes in Cx and Cs over
time. It is crucial that such drift be compensated, else false
detections, non- detections, and sensitivity shifts will follow.
The QT60161B can compensate for drift using two setups, ^H
and ^I.
2 Signal Processing
The device calibrates and processes signals using a number
of algorithms specifically designed to provide for high
survivability in the face of adverse environmental challenges.
The QT60161B provides a large number of processing
options which can be user-selected to implement very
flexible, robust keypanel solutions.
2.1 Negative Threshold
See also command ^A, page 21
The negative threshold value is established relative to a keys
signal reference value. The threshold is used to determine
key touch when crossed by a negative-going signal swing
after having been filtered by the detection integrator (Section
2.6). Larger absolute values of threshold desensitize keys
since the signal must travel farther in order to cross the
threshold level. Conversely, lower thresholds make keys
more sensitive.
As Cx and Cs drift, the reference point drift-compensates for
these changes at a user-settable rate (Section 2.4); the
threshold level is recomputed whenever the
reference point moves, and thus it also is drift
compensated.
Drift compensation is performed by making the reference
level track the raw signal at a slow rate, but only while there is
no detection in effect. The rate of adjustment must be
performed slowly, otherwise legitimate detections could be
ignored. The devices drift compensate using a slew-rate
limited change to the reference level; the threshold and
hysteresis values are slaved to this reference.
When a finger is sensed, the signal falls since the human
body acts to absorb charge from the cross-coupling between
X and Y lines. An isolated, untouched foreign object (a coin,
or a water film) will cause the signal to rise very slightly due to
the enhanced coupling thus created. These effects are
contrary to the way most capacitive sensors operate.
Once a finger is sensed, the drift compensation mechanism
ceases since the signal is legitimately detecting an object.
Drift compensation only works when the key signal in
question has not crossed the negative threshold level
(Section 2.1).
The drift compensation mechanism can be made asymmetric
if desired; the drift-compensation can be made to occur in
one direction faster than it does in the other simply by setting
^H and ^I to different settings.
Figure 1-6 Detection and Drift Compensation
The threshold is user-programmed on a per-key
basis using the setup process (Section 5).
Reference
2.2 Positive Threshold
See also command ^B, page 21
The positive threshold is used to provide a
mechanism for recalibration of the reference point
when a key's signal moves abruptly to the positive.
These transitions are described more fully in
Section 2.7.
Hysteresis
Threshold
Output
Signal
lQ
5 www.qprox.com QT60161B / R1.03

5 Page

QT60161B arduino
©Quantum Research Group Ltd.
Figure 3-2 Recommended Circuit Diagram
Noise sync: See also command ^W,
page 26. External fields can cause
interference leading to false
detections or sensitivity shifts. The
strongest external fields usually
come from AC power. RF noise
sources are heavily suppressed by
the low impedance nature of the QT
circuitry itself.
External noise only becomes a
problem if the noise is uncorrelated
with signal sampling; uncorrelated
noise can cause aliasing and beat
effects in the key signals. To
suppress this problem the devices
feature a noise sync input which
allows bursts to synchronize to the
noise source. This same input can
also be used to wake the part from a
low-power Sleep state.
The devices bursts can be
synchronized to an external source
of repetitive electrical signal, such as
50Hz or 60Hz, or possibly a video
display vertical sync line, using the
Sleep_wake / Noise sync line. The
noise sync operating mode is set by
command ^W. This feature allows
dominant external noise signals to
be heavily suppressed, since the
system and the noise become
synchronized and no longer beat or
alias with respect to each other. The
sync occurs only at the burst for key
0 (X0Y0); the device waits for the
sync signal for up to 100ms after the
end of a preceding full matrix scan
(after key #15), then when a negative
sync edge is received, the matrix is
scanned in its entirety again.
The sync signal drive should be a
buffered logic signal, or perhaps a
diode-clamped signal, but never a
raw AC signal from the mains.
command to the device. The part will wake and the null
command will not be processed. The MOSI line in turn
requires a pullup resistor to prevent the line from floating low
and causing an unintentional wake from sleep.
During Sleep the oscillator is shut down, and the part
hibernates with microamp levels of current drain. When the
part wakes, the part resumes normal functionality from the
point where it left off. It will not recalibrate keys or engage in
other unwarranted behavior.
Just before going to sleep the part will respond with a
response of 'Z'. In slave-only SPI mode (see Section 4.3), the
SS line must be floated high by the host as soon as it
receives this response; if SS does not float high, sleep will fail
and the device will instead completely reset after about 2
seconds. Upon waking the part will issue another 'Z' byte
back to the host.
Since Noise sync is highly effective
yet simple and inexpensive to implement, it is strongly
advised to take advantage of it anywhere there is a possibility
of encountering electric fields. Quantums QmBtn software
can show signal noise caused by nearby AC electric fields
and will hence assist in determining the need to make use of
this feature.
If the sync feature is enabled but no sync signal exists, the
sensor will continue to operate but with a delay of 100ms
from the end of one scan to the start of the next, and hence
will have a slow response time.
3.15 LED / Alert Output
Pin 40 is designed to drive a low-current LED, 5mA
maximum, in an active-low configuration. Higher currents can
cause significant level shifts on the die and are not advised.
The LED will glow brightly (i.e. pin 40 will be solid low) during
calibration of one or more keys, for example at startup. When
a key is detected, the LED will pulse low for the duration of
lQ
10 www.qprox.com QT60161B / R1.03

10 Page





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