One of the biggest design challenges with resistive touch solutions is getting accurate touch coordinates mapped to the specific underlying display via the touch screen. This is known as “calibration”.
Most resistive touch systems require a calibration step as one of the first steps in integration. Calibration of the touch sensor to the display is necessary because it is next to impossible to perfectly align the touch sensor’s coordinates to the underlying display. “Alignment” is a term used to describe the process of scaling and aligning the sensors’ anomalies to the display
Calibration can address the concern of touch sensor orientation during manufacturing. Consistent performance of the touch sensor is expected across different product platforms. However, many different pin-outs are associated with touch sensors and can be confusing when trying to produce different system platforms that may use touch screens of varying size or possibly even touch screens from different manufacturers. The different pin configurations of sensors can greatly affect the native operation of the touch controller.
In a scenario of developing and manufacturing two different product platforms, the platforms may use two different brands of touch sensors. Sensor manufacturer A uses one pin configuration, while sensor manufacturer B has the left and right sides switched on the pin configuration of the sensor’s tail. Both manufacturer A and B have great linearity specifications, and are highly responsive. However, manufacturer A has the origin (0,0) designated as the upper-left corner and manufacturer B has designated the upper-right corner as its origin. Calibration is critical to seamlessly re-map the orientation of the origin, allowing for consistently performing products regardless of the sensor’s pin configuration.
This also becomes an issue should the system’s touch sensor need replacement during its lifetime. If a particular manufacturer’s sensor may no longer be available, a second-source sensor may have to be used instead. This new sensor may not have the same orientation as the previous one, so the calibration must be able to correct any anomalies.