This article details and explains how Elo's AccuTouch technology works

See information below for an explanation of how the AccuTouch technology works.

 
 
The Parts of a Touchscreen
The AccuTouch five-wire resistive touchscreen uses a glass panel with a uniform resistive coating. A thick polyester coversheet is tightly suspended over the top of a glass substrate, separated by small, transparent insulating dots. The coversheet has a hard, durable coating on the outer side and a conductive coating on the inner side.

What Happens During a Touch
When the screen is touched, it pushes the conductive coating on the coversheet against the coating on the glass, making electrical contact. The voltages produced are the analog representation of the position touched.

How the Touchscreen Controller Interprets Screen Measurement
When the controller is waiting for a touch, the resistive layer of the touchscreen is biased at +5V through four drive lines, and the coversheet is grounded through a high resistance. When the touchscreen is not being touched, the voltage on the coversheet is zero. The voltage level of the coversheet 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 coversheet voltage and begins converting the coordinates as follows:

A    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 digitized by the ADC and subjected to an averaging algorithm, then stored for transmission to the host.
B    Next, the microprocessor places the Y drive voltage on the touchscreen by applying +5V to pins H and Y and grounding pin X and L. An analog voltage proportional to the Y (vertical position of the touch) now appears on the coversheet at pin S of the touchscreen connector. This signal is converted and processed as described above for the X position

Why the Averaging Algorithm is Important
The averaging algorithm reduces noise resulting from contact bounce during the making and breaking contact with the touchscreen. Successive X and Y 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 (then Y samples) fall within the range. The average of these values is used as the X and Y coordinates respectively.

Once independent X and Y samples are obtained, 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 independent X and Y sequence is restarted. Once acceptable coordinates have been obtained, an average coordinate is determined and communicated to the host processor.

Video Alignment
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 touchscreen to touchscreen. The AccuTouch controller can be calibrated for video alignment. This aligns the touchscreen coordinate system with the display image, reorients each axis, and scales the coordinates before they are transmitted to the host computer.

X- and Y-axis Measurements Originate from the Glass
AccuTouch five-wire technology utilizes the bottom glass substrate for both X- and Y-axis measurements. The flexible coversheet acts only as a voltage-measuring probe. This means that the touchscreen will continue working properly even with nonuniformity in the cover sheet's conductive coating. The result is an accurate, durable, and reliable touchscreen that offers drift free operation.