The potential measured at the isolated point is therefore too low to be detected.” 2E and 2F, the cloud of points absorbs a large part of the electrical potential of the fed column. Thus, the potential measured at the lower left corner of the sensor will be greater than the potential measured at the upper right corner.” “In fact, the resistance of the transparent material (ITO) composing the columns and the lines increases proportionately to the length of the tracks. The patent addresses two problems due to the high resistance: The columns and lines are made from ITO whose electrical resistance is quite high. You can find the modified schematic at Tekscan. To avoid the masking problem, the electronic schematic should be changed so that all inactive sensing lines are set to high-impedance. So, the contact point 1 will mask contact point 0 since the current from the 5V source directly goes to the corresponding grounded sensing line. In the above configuration, inactive sensing lines are grounded. In order to identify multiple touch points, I think that the sensing circuit need to be slightly modified. A column and a sensing line crossing the contact point 0 are currently selected: Practically this decision is done by a voltage comparator – thresholding.Īn example of multi-touch is shown below. Therefore, the touch can be determined by simply checking the measured voltage. When there is touch, the column and the sensing line are electrically connected and the measurement circuit detects an electrical potential. When there is no touch, the measured voltage is zero since current does not go to the measurement circuit. Other columns and sensing lines are set to high impedance and ground potential, respectively: 5V is applied to a column, and a voltage measurement circuit is attached to a horizontal sensing line. Let us first consider the case of single-touch. In the remaining part of this post, I’ll take the figure of the patent as a reference configuration. Unlike the above PMatrix illustration, the patent says that column lines are located at the bottom layer. In US 2007/0198926 A1, the PMatrix configuration is described in more detail. The top layer has ITO columns and bottom layer has ITO rows. It has two ITO (Indium Tin Oxide) patterned plates separated by spacing dots. This post will illustrate how the Stantum's touch screen works with your fingers. The big difference of those two is that Stantum manufactures multi-touch touch screens while Touchco offers opaque but flexible pressure sensitive multi-touch pads. Stantum and Touchco are two representative companies working on resistive multi-touch. Recently, resistive multi-touch has gained great attention.
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