Specifications

Theory of Operation 5
2. The microprocessor places the X drive voltage on the touchscreen by applying
+5V to Pins H and X and grounding Pins Y and L.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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, page 82.
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.
The DuraTouch Touchscreen
SmartSet controllers can operate with four-wire DuraTouch resistive
touchscreens, although these are no longer manufactured by Elo. For a description
of the touchscreen and the theory of operation, see the E261-280 DuraTouch
Serial Touchscreen Controller User's Manual.