Chapter
1 Introduction
The SmartSet controller
family is designed for use with Elo TouchSystems touchscreens. SmartSet controllers
provide the drive signals for the touchscreen, convert the received analog signals
into digital touch coordinates, and send them to the host computer. These controllers
are the result of twenty years of experience in controller engineering at Elo.
SmartSet
Controllers and Features
The following controllers
make up the SmartSet controller family.
- E271-2200 AccuTouch serial
RS-232 controller (obsolete)
- E271-2210 AccuTouch serial
RS232 controller
- E271-2201 AccuTouch PC-Bus
controller
- E271-2202 AccuTouch Micro
Channel controller (obsolete)
- E281-2300 IntelliTouch
serial RS-232 controller (obsolete)
- E281-2310 IntelliTouch
serial RS-232 controller (obsolete)
- 2500S IntelliTouch serial
RS232 controller
Features of SmartSet controllers
include:
- Sophisticated command
set and communication protocol consistent among the SmartSet controllers.
- Support for all AccuTouch®
or IntelliTouch® touchscreens.
- High speed -- can transmit
over 200 coordinates per second.
- Bi-directional communication
with acknowledgments.
- On-board calibration
and scaling of touch coordinates, untouch detection (lifting of the finger),
and programmable coordinate output rate.
- Configuration options
can be stored in nonvolatile RAM (NVRAM) or set with jumpers.
- Advanced four-layer surface-mount
design for small size and low profile. CMOS circuitry insures low power consumption.
Custom ASICs enhance reliability. Full power and ground planes enhance noise
immunity and radio frequency interference (RFI) immunity. Analog input filters
also eliminate electrical noise from the display. Rugged bipolar transistors
are used to drive the touchscreen and the output stage is protected by Raychem
PolySwitches. Linearity is preserved with a ratiometric measurement subsystem.
- Electrically and 100%
functionally tested with a microprocessor-controlled automated test set.
- Onboard diagnostics and
LED status indicators.
AccuTouch
E271-2210 Serial Controller
- Built around Elo's COACh
(Controller-On-A-Chip).
- Footprint: 3.3"
x 2.1".
- Maximum baud rate is
19.2K.
- Power requirements: 55ma
@ +5Vdc ±10% standby, 160ma average when touched, 240ma peak.
AccuTouch
E271-2201 PC-Bus Controller
- Half-slot PC-Bus controller
(for ISA and EISA systems).
- Host communication can
be polled or interrupt-driven.
- I/O address and interrupt
(IRQ) selectable through software or jumpers.
- AccuTouch E271-141 and
DuraTouch E271-142 controller emulation.
IntelliTouch
2500S Serial Controller
- Same footprint as the
AccuTouch E271-2210 controller.
- Compatible protocol with
the E271-2210 controller.
- Power requirements: 60ma
@ +5Vdc ±5%, 60ma typical.
Theory
of Operation
Each SmartSet
controller has the circuitry needed to interface an Elo touchscreen to a host
computer. Functionally, the circuitry may be divided into the following categories:
- Drive circuitry which
applies electrical signals to the touchscreen.
- A measurement subsystem
which detects and digitizes signals returned from the touchscreen.
- Interface circuitry (serial
or PC-Bus).
- A microprocessor which
directs the operation of the various controller subsystems.
- The following sections
describe how each of these component subsystems operate to measure coordinates
from an Elo touchscreen.
The
AccuTouch Touchscreen
- The AccuTouch Model
E274 touchscreen consists of a glass panel formed to match the shape of the
underlying display surface. A hard-coated plastic cover sheet is suspended
over the surface of the glass by tiny separator dots. The cover sheet may
be clear for best image clarity or have an antiglare finish. See Figure 1-1
below for detail on the construction of the AccuTouch touchscreen.
- The glass is covered
with a uniform resistive coating, and the plastic cover sheet has a conductive
coating. With a light touch on the cover sheet, the conductive coating on
the plastic contacts the resistive coating on the glass. There is an electrical
drive connection to each of the four corners of the resistive coating, and
a pickup connection to the coating on the cover sheet. When the proper DC
voltages are applied to the drive connections on the glass, the voltage at
the pickup connection is proportional to the position of the touch.

Figure 1-1. AccuTouch
Touchscreen
The logical sequence of
operation for the SmartSet controller, used in combination with the AccuTouch
touchscreen, is as follows:
- When the controller is
waiting for a touch, the resistive layer of the touchscreen (the coating on
the glass) is biased at +5V through all four drive lines, and the cover sheet
is grounded through a high resistance. When the touchscreen is not being touched,
the voltage on the cover sheet remains at zero. The voltage level of the cover
sheet is continuously converted by the analog to digital converter (ADC) and
monitored by the microprocessor on the controller. When the touchscreen is
touched, the microprocessor detects the rise in the voltage of the cover sheet
and begins coordinate conversion.
- The microprocessor places
the X drive voltage on the touchscreen by applying +5V to Pins H and X and
grounding Pins Y and L.
- An analog voltage proportional
to the X (horizontal) position of the touch appears on the cover sheet at
Pin S of the touchscreen connector. This voltage is then digitized by the
ADC and subjected to an averaging algorithm, then stored for transmission
to the host.
The averaging algorithm
reduces noise resulting from contact bounce during the making and breaking
of contact with the touchscreen. Successive X samples are tested to determine
that their values differ by no more than a certain range. If one or more
samples fall outside this range, the samples are discarded and the process
is restarted. This is continued until several successive X samples fall
within the range. The average of these values is used as the X coordinate.
- Next, the microprocessor
places the Y drive voltage on the touchscreen by applying +5V to Pins H and
Y and grounding Pins X and L.
- An analog voltage proportional
to the Y (vertical) position of the touch now appears on the cover sheet at
Pin S of the touchscreen connector. This signal is converted and processed
as described above for the X position.
- Successive coordinate
pairs are sampled to eliminate the effects of noise. If a sample does not
fall within an internal range, all X and Y coordinates are discarded and the
X sequence is restarted at step 2.
- Once acceptable coordinates
have been obtained, an average coordinate is determined and communicated to
the host processor.
Parameters for the internal
filtering algorithms can be adjusted through software setup. See Filter
command.
The X and Y values are similar
to Cartesian coordinates, with X increasing from left to right and Y increasing
from bottom to top. These absolute coordinates are arbitrary and unscaled, and
will vary slightly from unit to unit. The SmartSet controller can be calibrated
to align the touchscreen coordinate system with the display image, reorient
each axis, and scale the coordinates before they are transmitted to the host.
Because of the stability of the AccuTouch system, recalibration is not necessary
unless the position of the image changes.
The
IntelliTouch Touchscreen
The IntelliTouch
surface wave technology touchscreen consists of a glass panel molded to the
precise shape of a display's face. It may be clear for best image clarity or
treated for antiglare properties. Each axis of the touchscreen panel has a transmitting
and receiving piezoelectric transducer, and sets of reflector stripes. See Figure
1-2, below, for details on the construction of an IntelliTouch touchscreen.
Other variations
of the technology include SecureTouch, where the glass panel is up to
12mm thick and thermally or chemically strengthened, and iTouch touch-on-tube
technology, where the transducers and reflector stripes are placed directly
on the CRT faceplate glass, eliminating the need for a glass overlay.
Surface wave
energy is generated by the transmitting transducers mounted in the corners of
the touchscreen. The touchscreen controller sends a 5.53 MHz electrical signal
to the X-axis transmitting transducer which converts the signal into surface
waves. A set of reflector stripes located on the lower edge of the glass reflects
these waves across the active area of the glass. Reflector stripes at the top
gather the reflected waves and direct them to the X-axis receiving transducer
which reconverts the surface waves into an electrical signal.

Figure 1-2.
IntelliTouch Touchscreen
About
This Manual
This manual
provides technical information on the Elo SmartSet touchscreen controller family.
Details are given in this manual on the features, configurations, connections,
and specifications of the SmartSet controllers.
This manual
also includes examples of writing a software interface, such as a device driver,
for the controller. Elo supplies a variety of drivers including its MonitorMouse®
family of mouse emulation drivers for DOS, Microsoft Windows (3.x, NT, 95, 98,
ME, 2000, XP, CE, etc.), OS/2, Macintosh, and Linux. Other third-party drivers
and interfaces are also available. See www.elotouch.com
or contact Elo before writing your own driver.
The SmartSet
Companion Disk, which may be downloaded from www.elotouch.com,
contains the sample driver source code and the SmartSet software setup utility,
both described in this manual. See the !READ.ME! file, if present, for any changes
or additions to this manual.
The rest of
this manual is organized as follows:
Chapter
2 Explains how to set up the controllers via jumpers.
Chapter
3 Details the controller connections and installation procedures.
Chapter
4 Gives a tutorial on the important operating characteristics of the SmartSet
controller interface using the SmartSet software setup utility.
Chapter
5 Describes the communication protocol for the controllers and provides
the information you'll need for writing a software interface. Example C code
is included.
Chapter
6 Provides a command reference for the SmartSet controller software interface.
Appendix
A Details optional data output formats and emulation modes.
Appendix
B Gives algorithms for coordinate scaling.
For more information
on the AccuTouch or IntelliTouch product lines, including touchscreen and controller
options, installation, and troubleshooting, see the AccuTouch Product Manual
and IntelliTouch Product Manual respectively, available for download on www.elotouch.com.