Quantum E240 Manuel utilisateur
16
E240
User Manual
OVERVIEW
The E240 is designed to let you evaluate and develop with the QT240 4 key QTouch™ IC. It
includes four independent touch sensitive electrodes with corresponding LEDs to indicate
touch. Connections are provided for external interfacing. The E240 is powered from an
external 7V to 12V DC source (such as a common 9V battery).
For more detailed information about this product please refer to the latest QT240
datasheet at www.qprox.com/datasheets.
Materials Provided:
1 x Clear plastic panel
1 x E240 self-adhesive eval board with battery clip
1 x 9V battery
4 x Rubber feet
2 x Sample QT240-ISS chips
1 x QRG product CD-ROM (with QT240 datasheet but check website for latest)
1 x User guide
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1
BOARD MOUNTING
The E240 can be adhered to plastic, glass, or any other dielectric panel with its peel-back
adhesive strip. You do not have to use the supplied panel if you would rather stick it on your own
panel. Here’s how to mount it:
1Place the plastic panel face down on a table; tape down the edges of the panel to the table
so it cannot move.
2Remove the peel-back paper from the E240 PCB and adhere the E240 to the back of the
panel. Flex the E240 slightly while pressing down lightly on it to help eliminate trapped air.
Take care to flex the board only slightly to prevent the delicate SMT parts on the board from
cracking and failing.
Tip: Line up the PCB with the alignment marks on the back of the slider panel. The PCB must
be positioned as shown below so that the keys line up with the graphics.
3 Un-tape the board from the table, and mount the four rubber feet as shown above to make
the E240 mechanically stable in use.
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2
RUNNING THE E240
To run the E240, simply:
1Place the E240 on a table, touch side up.
2Connect the 9V battery while making sure your fingers are clear of the touch areas to allow
proper no-signal calibration.
The E240 is now ready to use! Touch the keys to see the LEDs light up.
A continuous touch of 10 seconds will cause the key to recalibrate. Releasing the key
after such an event and waiting a few seconds will cause the key to recalibrate yet again,
and the key will function normally thereafter.
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3
THEORY OF OPERATION
The E240 scans the keys using bursts of charge-transfer pulses. Immediately after power up, the
signals from these bursts are used to calibrate the baseline reference values of the keys. This
makes the device highly adaptive to mechanical differences (i.e. varying panel thicknesses). The
QT240 chip also performs drift compensation on a continuous basis, so that the signals are
constantly being adjusted at a slow rate to accommodate drift.
The calibration process (done at power-up) should be performed in a ‘not disturbed’
neutral condition, i.e. all fingers away from the keys and with the board situated in the
location where it will be used. Changes in location can alter the amount of signal coupling
from the board back to the local environment and thereby change the sensitivity of the
keys. If the calibrations are in error, just leaving the board alone for up to 30 seconds will
allow the drift calibration process to settle the keys into the correct calibration values.
The QT240 features spread-spectrum pulse modulation which heavily suppresses external noise
effects, while also suppressing radiated emissions. This powerful feature provides for highly
reliable, compliant operation under a wide variety of operating conditions.
The QT240 chip also uses a ‘Detect Integrator’ to protect against false detection reporting by
verifying that a key is reporting touch for 6 bursts in a row; if the device fails to detect a touch
during any of these 6 signal samples the chip will refuse to report a key touch on an Out pin.
Combined with spread-spectrum operation, the detect integration process provides a powerful
mechanism to suppress false detections from external noise sources.
If a key is touched for longer than 10 seconds, the key is flagged as a ‘stuck key’ and the QT240
recalibrates it so that the corresponding LED will go out, and the key will operate again normally
while suppressing the object (ie, a touch) that caused the prolonged detection. Only the ‘stuck
key’ is recalibrated, as all electrodes operate independently. The 10s timeout can be changed to
60s or infinite with jumpers; see page 10 for details.
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4
BOARD DETAILS
The E240 is a simple double-sided PCB on industry standard FR4 material. All parts are
standard surface mount types. Here is a brief description of some of the parts and features.
Keys — Keys consists of capacitive electrodes formed using copper areas on the E240 which
project a capacitive field through the overlying dielectric panel material.
Electrodes — Copper areas on the PCB which define the touch keys.
LEDs — The board has one ‘Power’ LED which remains on as long as the board is powered,
plus one LED per key to indicate touch.
Connector CN1 — The main interface connector is located at one end of the E240 board. The
pinout of this connector is shown in Table 1 (next page). The pin functions are as follows:
[1] SYNC — Not used in fast mode (the default setting). SYNC is available in slow mode
only and is used to synchronize the E240 burst with an external falling edge signal,
usually derived from a 50 or 60Hz source to suppress mains interference, or to allow
two or more QT240 chips to synchronize to to each other, to prevent cross-interference
effects between the adjacent keys of different chips.
[2..5] OUT ‘A’ ~ OUT ’D’ — OUT pins are low when the corresponding key is inactive and
high when active, and are controlled by the QT240 chip. These lines also control the
LEDs.
[6] /RESET — Can be left floating, as the board has its own internal reset circuit. To reset
the E240 externally (for example to force all keys to recalibrate), connect RESET to
GND for at least 1ms, then release it; the board will restart, recalibrate and be ready to
detect touches again after about 180ms.
[7, 8] +POWER, GND — Use +7 to +12VDC connected between the +POWER and GND to
power the E240 board. The battery snap feeds the same two connections, and can also
be used for power input.
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5
BOARD LAYOUT
Figure 1 —
Board Layout
Electrodes
(on user side)
Battery Connector
Connector (CN1)
Table 1 — Connector (CN1) Pinout
Pin Description Pin Description
1 SYNC 5 OUT ‘A’
2 OUT ‘D’ 6 /RESET
3 OUT ‘C’
7 GND (Ground, 0V)
4 OUT ‘B’ 8 +POWER (+7 .. +12V)
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9
BOARD OPTIONS
Warning: Changing components on the board involves soldering and unsoldering; please take
care not to overheat the board or to leave excessive flux which can affect signal stability
and performance. If in doubt, clean the board with a commercial flux remover and dry it prior to
use.
Figure 5 — Jumper Positions Showing Default Configuration
The E240 as shipped is factory configured to operate in fast mode with spread spectrum
enabled, and with a 10-second recalibration delay. The user can re-configure the jumpers to
change these settings using zero-ohm 0603 SMD resistors or bits of fine wire.
See next page for available jumper combinations.
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