that increments with each detection until a limit is reached,
after which the output is activated. If no detection is sensed
prior to the final count, the counter is reset immediately to
zero. The required count is 4.
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 nominal Max On-Duration timeouts are
The Detection Integrator can also be viewed as a 'consensus' available: 10 and 60 seconds.
filter, that requires four detections in four successive bursts to
2.2.2 TOGGLE
M
ODE
O
UTPUT
create an output. As the basic burst spacing is 95ms, if this
spacing was maintained through 4 consecutive bursts the
sensor would be very slow to respond. In the QT118H, after
an initial detection is sensed, the remaining three bursts are
spaced only about 2ms apart, so that the slowest reaction
time possible is the fastest possible.
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.
2.1.5 FORCED
S
ENSOR
R
ECALIBRATION
The QT118H has no recalibration pin; a forced recalibration
is accomplished only when the device is powered up.
However, the supply drain is so low it is a simple matter to
treat the entire IC as a controllable load; simply driving the
QT118H's Vdd pin directly from another logic gate or a
microprocessor port (Figure 2-2) will serve as both power and
'forced recal'. The source resistance of most CMOS gates
and microprocessors is low enough to provide direct power
without any problems. Almost any CMOS logic gate can
directly power the QT118H.
Table 2-1 Output Mode Strap Options
Tie
Pin 3 to:
Tie
Pin 4 to:
Max On-
Duration
Vdd
Vdd
Gnd
Gnd
Vdd
Gnd
Gnd
Vdd
10s
60s
10s
10s
DC Out
DC Out
Toggle
Pulse
A 0.01uF minimum bypass capacitor close to the device is
essential; without it the device can break into high frequency
oscillation.
2.2.3 PULSE
M
ODE
O
UTPUT
This generates a positive pulse of 95ms duration with every
new detection. It is most useful for 2-wire operation (see
Figure 1-2), 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.
Option strap configurations are read by the QT118H only on
powerup. Configurations can only be changed by powering
the QT118H down and back up again; a microcontroller can
directly alter most of the configurations and cycle power to
put them in effect.
Max On-Duration is fixed at 10 seconds if in Pulse output
mode.
2.2 OUTPUT FEATURES
The QT118H is designed for maximum flexibility and can
accommodate most popular sensing requirements. These
are selectable using strap options on pins OPT1 and OPT2.
All options are shown in Table 2-1.
The piezo beeper drive does not operate in Pulse mode.
2.2.4 HEARTBEAT™ OUTPUT
The output has a full-time HeartBeat™ ‘health’ indicator
superimposed on it. This operates by taking 'Out' into a
tri-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.
OPT1 and OPT2 should never be left floating. If they are
floated, the device will draw excess power and the options
will not be properly read on powerup. Intentionally, there are
no pullup resistors on these lines, since pullup resistors add
to power drain if the pin(s) are tied low.
Since Out is normally low, a pullup resistor will create positive
HeartBeat pulses (Figure 2-3) 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.
2.2.1 DC MODE
O
UTPUT
The output of the device can respond in a ‘DC mode’, where
the output is active-high upon detection. The output will
remain active for the duration of the detection, or until the
If the sensor is wired to a microcontroller as shown in Figure
2-4, 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.
Figure 2-2 Powering From a CMOS Port Pin
PORT X.m
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 2-5).
0.01µF
C MO S
m ic rocontroller
Vdd
PORT X.n
OUT
QT118
Vss
lq
5
QT118H R1.08 / 0405
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