QT110-D View Datasheet(PDF) - Quantum Research Group
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QT110-D Datasheet PDF : 12 Pages
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Figure 2-2 Powering From a CMOS Port Pin
P O RT X .m
CMOS
m icro controller
P O RT X .n
O UT
0.01µF
Vdd
Q T110
Vss
Figure 2-3 Damping Piezo Clicks with Rs
+2.5 ~ +5
1
2
Vdd
7
OUT
SNS1
3
OPT1
5
GAIN
4
OPT2
6
SNS2
Vss
8
RE
Rs
SENSING
ELECTRODE
Cx
detection, or until the Max On-Duration expires, whichever
occurs first. If the latter occurs first, the sensor performs a full
recalibration and the output becomes inactive until the next
detection.
In this mode, two Max On-Duration timeouts are available: 10
and 60 seconds.
2.2.2 TOGGLE MODE OUTPUT
This makes the sensor respond in an on/off mode like a flip
flop. It is most useful for controlling power loads, for example in
kitchen appliances, power tools, light switches, etc.
Max On-Duration in Toggle mode is fixed at 10 seconds. When
a timeout occurs, the sensor recalibrates but leaves the output
state unchanged.
Table 2-1 Output Mode Strap Options
Tie
Pin 3 to:
Tie
Pin 4 to:
Max On-
Duration
DC Out
Vdd
Vdd
10s
DC Out
Vdd
Gnd
60s
Toggle
Gnd
Gnd
10s
Pulse
Gnd
Vdd
10s
2.2.3 PULSE MODE OUTPUT
This mode generates a pulse of 75ms duration (QT110 -
negative-going; QT110H - positive-going) with every new
detection. It is most useful for 2-wire operation, but can also be
used when bussing together several devices onto a common
output line with the help of steering diodes or logic gates, in
order to control a common load from several places.
Max On-Duration is fixed at 10 seconds if in Pulse output
mode.
Note that the beeper drive does not operate in Pulse mode.
2.2.4 PIEZO ACOUSTIC DRIVE
A piezo drive signal is generated for use with a piezo sounder
immediately after a detection is made; the tone lasts for a
nominal 95ms to create a ‘tactile feedback’ sound.
The sensor drives the piezo using an H-bridge configuration for
the highest possible sound level. The piezo is connected
across pins SNS1 and SNS2 in place of Cs or in addition to a
parallel Cs capacitor. The piezo sounder should be selected to
have a peak acoustic output in the 3.5kHz to 4.5kHz region.
Since piezo sounders are merely high-K ceramic capacitors,
the sounder will double as the Cs capacitor, and the piezo's
metal disc can even act as the sensing electrode. Piezo
transducer capacitances typically range from 6nF to 30nF in
value; at the lower end of this range an additional capacitor
should be added to bring the total Cs across SNS1 and SNS2
to at least 10nF, or possibly more if Cx is above 5pF
Piezo sounders have very high, uncharacterized thermal
coefficients and should not be used if fast temperature swings
are anticipated, especially at high gains. They are also
generally unstable at high gains; even if the total value of Cs is
largely from an added capacitor the piezo can cause periodic
false detections.
The burst acquisition process induces a small but audible
voltage step across the piezo resonator, which occurs when
SNS1 and SNS2 rapidly discharge residual voltage stored on
the resonator. The resulting slight clicking sound can be greatly
reduced by placing a 470K resistor Rs in parallel with the
resonator; this acts to slowly discharge the resonator,
attenuating of the harmonic-rich audible step (Figure 2-3).
Note that the piezo drive does not operate in Pulse mode.
2.2.5 HEARTBEAT™ OUTPUT
The output has a full-time HeartBeat™ ‘health’ indicator
superimposed on it. This operates by taking 'Out' into a 3-state
mode for 350µs once before every QT burst. This output state
can be used to determine that the sensor is operating properly,
or, it can be ignored using one of several simple methods.
QT110: The HeartBeat indicator can be sampled by using a
pulldown resistor on Out, and feeding the resulting
negative-going pulse into a counter, flip flop, one-shot, or other
circuit. Since Out is normally high, a pulldown resistor will
create negative HeartBeat pulses (Figure 2-4) when the sensor
is not detecting an object; when detecting an object, the output
will remain active for the duration of the detection, and no
HeartBeat pulse will be evident.
QT110H: Same as QT110 but inverted logic (use a pull-up
resistor instead of a pull-down).
If the sensor is wired to a microcontroller as shown in Figure
2-5, the controller can reconfigure the load resistor to either
ground or Vcc depending on the output state of the device, so
that the pulses are evident in either state.
Electromechanical devices will usually ignore this short pulse.
The pulse also has too low a duty cycle to visibly activate
LED’s. It can be filtered completely if desired, by adding an RC
timeconstant to filter the output, or if interfacing directly and
only to a high-impedance CMOS input, by doing nothing or at
most adding a small non-critical capacitor from Out to ground
(Figure 2-6).
2.2.6 OUTPUT DRIVE
The QT110’s output is active low (QT110) or active high
(QT110H) and can source 1mA or sink 5mA of non-inductive
current.
LQ
5
QT110/110H R1.03/0604
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