Game Development Reference
used at any given time. The general layout is given in Figure 20-2 . The squares containing
the X and Y wires would actually be overlapped but are shown skewed here for clarity.
Figure 20-2. Four-wire touch screen
The reason for calling it a four-wire touch screen should now be obvious; however,
remember that only three of the wires will be active at any time. The basic structure is
shown in Figure 20-3 .
Figure 20-3. Four-wire touch screen profile
The first layer of the screen comprises a flexible conductor separated by an insulating
gap. Under the gap lies a solid conductor. When a finger presses down on the outer layer
of flexible conductor, it crosses the gap and makes contact with the solid conductor. The
conductors are thin layers of indium-tin oxide (ITO) with silver bus bars on either end
of the sheet, shown as black lines in Figure 20-2 .