A basic capacitive touch sensor works on the principle of capacitance, which is the ability of a system to store an electric charge. Capacitance is formed between two conductive objects separated by an insulating material. In the case of a touch sensor, these conductive objects are typically electrodes, and the insulating material is the surface where the touch sensor is placed.
The working principle of a basic capacitive touch sensor can be broken down into the following steps:
Electrode arrangement: The touch sensor is constructed with at least two electrodes, usually in the form of conductive pads or layers, placed on or beneath the surface of the touch-sensitive area. For example, a simple setup could involve a single electrode acting as the transmitter and another electrode as the receiver.
Electric field generation: When the touch sensor is powered, an AC (alternating current) signal is applied to one of the electrodes (the transmitter). This generates an electric field around the electrodes, which extends to the surface of the touch-sensitive area.
No touch situation: In the absence of a touch, the electric field between the two electrodes is uniform, and the capacitive touch sensor measures a baseline capacitance.
Touch detection: When a conductive object (e.g., a human finger) comes close to or touches the surface of the touch sensor, it disrupts the electric field between the electrodes. This causes a change in capacitance between the electrodes.
Capacitance change: The presence of a conductive object creates a small capacitance coupling between the touch sensor's electrodes. The change in capacitance is detected by the touch sensor's controller or IC (integrated circuit).
Signal processing: The touch sensor's controller processes the capacitance change and determines if a touch event has occurred. This controller can filter out noise and perform calculations to detect the position and strength of the touch.
Output: Once a touch is detected and processed, the touch sensor's controller sends the corresponding data to the device's main processor or the system it is integrated with. The system then interprets this data and responds accordingly, triggering the desired action, such as input recognition, button press, or gesture recognition.
It is important to note that capacitive touch sensors can be more complex in real-world applications, involving multiple electrodes and more advanced algorithms for touch detection and noise reduction. Additionally, touchscreens often employ a grid of electrodes to enable multi-touch functionality and improve accuracy. However, the fundamental working principle remains based on the change in capacitance caused by the presence of a conductive object near or touching the touch sensor's surface.