PTC QTouch® library supports design of sliders using both self and mutual capacitance methods.
Self-capacitance acquisition method is suitable for designing small sliders (typically 20 – 60mm). PTC QTouch library supports only three channel slider for self-capacitance method. To design long slider sensor with self-capacitance method, the size of the sensor electrodes needs to be increased. Larger sensor electrodes will have higher self-capacitance. This may saturate the sensor exceeding the maximum limit of electrode capacitance measurable by PTC. Hence it is not suitable to design long sliders using self-capacitance method.
Mutual capacitance slider sensor is constructed from a series of electrodes located in close proximity to each other. All sensor electrodes are directly connected to X lines of the chip along with a common Y line. Using standard slider techniques, the number of series electrodes are used to determine the physical length of the sensor. PTC QTouch library can be used to create a mutual capacitance slider using between three to eight channels. A slider with approximately 68mm length can be achieved by using eight electrodes with 8mm width and a gap of 0.5mm between the electrodes. It is possible to design mutual-capacitance sliders much longer than 68mm when hardware interpolation techniques are used.