l Q QT401
QSLIDE TOUCH SLIDER IC
zz zz 1-dimensional finger-touch slider
VDD 1 14 GND
zz zz Extremely simple circuit - no external active components
z Completely passive sensing strip: no moving parts
SDO 2 13 DRDY
z Compatible with clear ITO over LCD construction
/SS 3 QT401 12 DETECT
z z SPI slave-mode interface
z z
SCLK 4 11 PROX
zz zz Self-calibration and drift compensation modes
10
SDI 5 N/A
zz zz Proximity mode for wake up of a product
z Spread-spectrum operation for optimal EMC compliance
SNS1A 6 9 SNS2A
zz zz 2.5 - 5.5V single supply operation; very low power
8
SNS1B 7 SNS2B
z z 14-pin SOIC, TSSOP lead-free packages
z z
z Inexpensive, simple 1-sided PCB construction possible
z z E401 reference design board available
z z
APPLICATIONS
y Lighting controls y Appliance controls y Touch-screens y Automotive controls
The QT401 QSlide IC is a 1-dimensional position sensor IC designed for human interfaces. This unique IC allows designers
to create speed or volume controls, menu bars, and other more exotic forms of human interface on the panel of an appliance
or over an LCD display.
The device uses a simple, inexpensive resistive sensing strip between two connection end points. The strip element can be an
arc or a semicircle or simply linear. The strip can also be used as a proximity sensor out to several centimeters, to wake up an
appliance or display from a sleep mode in a dramatic fashion.
The QT401 can report a single rapid touch anywhere along the slider element, or, it can track a finger moving laterally along
the slider strip in real time. The device self-calibrates under command from a host controller in one of two modes.
The QT401 is a new type of capacitive sensor based on Quantums patented charge-transfer methods. This device uses two
channels of simultaneous sensing across a resistive element to determine finger position, using mathematical analysis. The
accuracy of QSlide is theoretically the same as a conventional potentiometer. A positional accuracy of 5% (or better) is
relatively easy to achieve.
The acquisitions are performed in a burst mode which uses proprietary spread-spectrum modulation for superior noise
immunity and low emissions.
The output of the QT401 can also be used to create discrete controls on a strip, by interpreting sets of number ranges as
buttons. For example, the number range 0..19 can be button A, 30..49 button B, 60..79 button C etc. Continuous slider action
and discrete controls can be mixed on a single strip, or, the strip can be reinterpreted differently at different times, for example
when used below or on top of an LCD to act as a menu input device that dynamically changes function in context. In this
fashion the QT401 can be used to create ultra-simple, extremely inexpensive touch screens. The device is compatible with
ITO (Indium Tin Oxide) overlays on top of various displays.
AVAILABLE OPTIONS
T SO-14 TSSOP-14
A
0 0
-40 C ~ +85 C QT401-ISG QT401-ISSG
L Q Copyright 2004 QRG Ltd
QT401 R10.04/0505Figure 1-1 QT401 Wiring Diagram
1 Operation
The QT401 uses a SPI slave mode interface for control
VIN Regulator 1
QT401
and data communications with a host controller.
VDD
VIN VOUT
Acquisition timings and operating parameters are
C1 C2 8
R1
GND SNS2B
under host control; there are no option jumpers and the
127
2.2uF 2.2uF 22k
Cs2
device cannot operate in a stand-alone mode.
100nF
9
SNS2A
R2
The positional output data is a 7-bit binary integer
100k
Slider Element
(0...127) indicating position from left (0) to right (127).
13
DRDY 60K~150K ohms
2
Like all QProx devices, the QT401 operates using total resistance
SDO
R3
3
bursts of charge-transfer pulses; burst mode permits /SS
SPI BUS
1K
4 6
an unusually high level of control over spectral SCLK SNS1A
Cs1
5
SDI
modulation, power consumption, and response time.
100nF
0
Proximity
11 7
PROX SNS1B
The QT401 modulates its bursts in a spread-spectrum
fashion in order to heavily suppress the effects of Touch Detect 12
DETECT
VSS
external noise, and to suppress RF emissions.
C3 1nF C4 1nF
1.1 Synchronized Mode
Refer also to Figure 3-1, page 6.
Mains Sync: Sync mode can be used to sync to mains
Sync mode allows the host device to control the rep etition
frequency via the host controller, if mains interference is
rate of the acquisition bursts, which in turn govern response
possible (ie, running as a lamp dimmer control). The host
time and power consumption. The maximum spacing from the
should issue SPI commands synchronously with the mains
end of one burst to the start of the next in this mode is 1
frequency. This form of operation will heavily suppress
second.
interference from low frequency sources (e.g. 50/60Hz),
In sync mode, the device will wait for the SPI slave select line
which are not easily suppressed using spread-spectrum burst
/SS to fall and rise and will then do an acquisition burst;
modulation.
actual SPI clocks and data are optional. The /SS pin thus
Cross-talk suppression: If two more QT401s are used in
becomes a sync input in addition to acting as the SPI
close proximity, or there are other QTouch type device(s)
framing control.
close by, the devices can interfere strongly with one another
Within 35s of the last rising edge of CLK, the device will
to create position jitter or false triggering. This can be
enter a low power sleep mode. The rising edge of /SS must
suppressed by making sure that the devices do not perform
occur after this time; when /SS rises, the device wakes from
acquisition bursts at overlapping times. The host controller
sleep, and shortly thereafter does an acquisition burst. If a
can make sure that all such devices operate in distinctly
more substantial sleep time is desired, /SS should be made
different timeslots, by using a separate /SS line or Sync
to rise some delay period later.
signal for each part.
By increasing the amount of time spent in sleep mode, the
host can decrease the average current drain at the expense
1.2 Free-Run Mode
of response time. Since a burst typically requires 31ms (at
If /SS stays high, the device will acquire on its own
3.3V, reference circuit), and an acceptable response time
repetitively approximately every 60ms (Figure 1-2). This
might be ~100ms, the power duty cycle will be 31/100 or 31%
mode can be used to allow the part to function as a prox or
of peak current.
touch detector first, perhaps to wake a host controller. Either
the PROX or DETECT can be used as a wakeup.
If power is not an issue the device can run constantly under
host control, by always raising /SS after 35s from the last
In free-run mode, the device does not sleep between acquire
rising edge of CLK. Constant burst operation can be used by
bursts. In this mode the QT401 performs automatic drift
the host to gather more data to filter the position data further
compensation at the maximum rate of one count per 180
to suppress noise effects, if required.
acquisition burst cycles, or about one count every 3 seconds
without host intervention. It is not possible to change this
Figure 1-2 Free-Run Timing Diagram ( /SS = high )
~31ms ~31ms
Acquire Bur
~3.8ms ~30us
DRDY from QT
~25ms
lQ 2 QT401 R10.04/0505
14