at42qt113b ATMEL Corporation, at42qt113b Datasheet - Page 11

• Manufacturer Part Number: at42qt113b
• Manufacturer: ATMEL Corporation

3.2.3
3.2.4
9525B–AT42–09/10
Toggle Mode Output
HeartBeat™ Output
Infinite timeout is useful in applications where a prolonged detection can occur and where the
output must reflect the detection no matter how long. In infinite timeout mode, the designer
should take care to be sure that drift in Cs, Cx, and Vdd do not cause the device to “stick on”
inadvertently even when the target object is removed from the sense field.
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.
Max On-Duration in Toggle mode is fixed at 10 seconds. When a timeout occurs, the sensor
recalibrates but leaves the output toggle state unchanged.
The QT113B output has a full-time HeartBeat™ health indicator superimposed on it. This
operates by taking OUT into a 3-state mode for 300µs once after 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.
The HeartBeat indicator can be sampled by using a pull-down 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 pull-down resistor will create negative HeartBeat pulses (see
page
remain low for the duration of the detection, and no HeartBeat pulse will be evident.
Figure 3-3.
If the sensor is wired to a microcontroller as shown in
reconfigure the load resistor to either ground or Vdd depending on the output state of the
QT113B, so that the pulses are evident in either state.
Figure 3-4.
11) when the sensor is not detecting an object; when detecting an object, the output will
Getting HeartBeat Pulses With a Pull-down Resistor
Using a Micro to Obtain HeartBeat Pulses In Either Output State
Microcontroller
HeartBeat™ Pulses
Ro
PORT_M.x
PORT_M.y
2
3
4
OUT
OPT1
OPT2
Vdd
1
8
R
Vdd
Vss
o
SNS2
GAIN
SNS1
7
5
6
2
3
4
OUT
OPT1
OPT2
SNS2
GAIN
SNS1
Figure
7
5
6
3-4, the microcontroller can
AT42QT113B
Figure 3-3 on
11