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.

The Detection Integrator can also be viewed as a 'consensus'

filter, that requires four detections in four successive bursts to

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.

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.

A 0.01uF minimum bypass capacitor close to the device is

essential; without it the device can break into high frequency

oscillation.

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.

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.

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.

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

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

available: 10 and 60 seconds.

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.

10s

Vdd

Gnd

Pulse

10s

Gnd

Gnd

Toggle

60s

Gnd

Vdd

DC Out

10s

Vdd

Vdd

DC Out

Max On-

Duration

Tie

Pin 4 to:

Tie

Pin 3 to:

Table 2-1 Output Mode Strap Options

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.

Max On-Duration is fixed at 10 seconds if in Pulse output

mode.

The piezo beeper drive does not operate in Pulse mode.

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.

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.

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.

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).

5

QT118H R1.08 / 0405

Figure 2-2 Powering From a CMOS Port Pin

0.01µ F

C M O S

m ic rocon troller

OUT

P ORT X. m

P ORT X. n

Vdd

Vss

QT11 8