Water-resistant Algorithms

Solomon Systech demonstrated water-resistance on a 4-inch, true single-layer, mutual-capacitance smartphone touch panel. Note the spray bottle of water on the left and the large number of water droplets on the screen. Photo by author.

Demonstrations of touch-panel water resistance can be seen in a number of booths at Display Week this year; it’s part of the trend of enhancing projected-capacitive (p-cap) touch to make it more environmentally resistant. 

Most often, water-resistance is achieved by operating a touch-panel in two modes and switching back and forth between them: self-capacitance (using only the top electrode layer) and mutual capacitance (using both electrode layers). Self-capacitance is unaffected by water, while mutual capacitive sees water as a touch.

Solomon Systech, a Hong-Kong-based touch controller supplier, demonstrated water resistance using only algorithmic support on a 4-inch, true single-layer, mutual-capacitance p-cap touch-panel. This is an achievement because it’s very difficult to distinguish water droplets from touches using only mutual capacitance. I asked if perhaps the Solomon Systech controller was using only a portion of the single-layer electrode in self-capacitance mode, and the booth representative insisted that the water resistance was accomplished purely via mutual-capacitance algorithms running on the touch controller.

True single-layer mutual-capacitance touch-panels have rapidly become the configuration of choice for low-end smartphones due to their low cost; Solomon Systech’s ability to support more advanced functionality such as water-resistance purely through mutual-capacitance firmware provides an interesting illustration of how the capability of p-cap touch is continuing to expand even at the very low end.  --Geoff Walker