A basic capacitive touch sensor operates on the principle of capacitance. Capacitance is a property of an electrical system that describes its ability to store an electrical charge. The touch sensor uses this property to detect when a conductive object, such as a finger, comes in contact with the sensor's surface.
Here's a simplified explanation of how a basic capacitive touch sensor works:
Construction: The touch sensor consists of two conductive layers separated by a non-conductive material or a dielectric. The first layer, also known as the sensing or transmitting layer, generates an electrical signal, usually a high-frequency AC signal. The second layer, the receiving or sensing layer, is responsible for measuring changes in the electrical properties of the first layer caused by touch interactions.
Electric Field: When the sensor is not touched, the two conductive layers are separated by the dielectric material. The transmitting layer applies an electrical charge, creating an electric field between the two layers.
Touch Interaction: When a conductive object (like a finger) approaches the touch sensor's surface or comes in direct contact with it, it disrupts the electric field. This causes a change in capacitance between the transmitting and sensing layers.
Capacitance Change: The presence of the conductive object alters the capacitance of the sensor. The capacitance increases when the object is near or touches the surface and decreases when the object is removed.
Sensing Circuit: The touch sensor's sensing circuit continually monitors the capacitance changes in the transmitting and sensing layers. It detects these variations and interprets them as touch events.
Signal Processing: The raw data from the sensing circuit undergoes signal processing to filter out noise and interference. The touch controller interprets the processed data to determine the touch coordinates and registers the touch event.
Output: The touch controller then sends the touch event information to the device's operating system, enabling the device to respond to user interactions appropriately. For example, it may trigger actions like tapping, dragging, or multi-touch gestures.
It's essential to note that capacitive touch sensors require conductive objects like the human body to function effectively. Therefore, they do not work with non-conductive materials like gloves or styluses (unless specifically designed for capacitive touchscreens). Modern touch sensors have additional features like multi-touch support, palm rejection, and various other improvements to enhance their functionality and accuracy.