Capacitive Sensing

Capacitive sensing is a technology based on capacitive coupling that takes human body capacitance as an input. It is commonly used in touch sensors, where it detects the presence or absence of a touch by a human finger or hand. This technology is now prevalent in a multitude of devices, ranging from smartphones to various interactive surfaces.

Principles of Capacitive Sensing

Capacitive sensing works by detecting changes in capacitance. Everything has capacitance, which is the ability to store an electric charge. A capacitive sensor has one or more conductive pads that are designed to interact with their environment in a capacitive way.

When a conductive object, like a finger, gets close to the sensor area, it alters with the local electrostatic field, changing the capacitance of the system. This change can be detected and measured. The sensor pad is one plate of a capacitor, with the other plate being either the conductive object or a reference ground plane.

The two main types of capacitive sensing are:

Self-capacitance: This measures the change in capacitance of a single electrode when a finger touches it. It's very sensitive and is often used for single-touch sensing.

Mutual capacitance: This measures the capacitance between two electrodes when a finger touches them. It's more complex than self-capacitance but can detect multiple touches at once.

Capacitive sensors are often integrated with an array of electrodes and a driving circuit that constantly measures the capacitance of each electrode. Signal processing is used to determine the exact location and nature of the touch event.

Applications in Touch Interfaces

You've probably used capacitive sensing without even realizing it-- it's the technology that makes touch screens work on your smartphone, tablet, laptop, and other devices. Capacitive sensing works by detecting the change in electrical charge when your finger touches the screen. This allows for multi-touch gestures like pinching and swiping. Capacitive sensing is also used in automotive controls, interactive kiosks, and ATMs. It's versatile & becoming more and more common in our everyday lives.

See: TI CapSense Guide