What Is a Capacitive Touch Sensor?
A capacitive touch sensor is a device that detects changes in capacitance in an electric field.
Capacitance refers to the amount of stored charge in a conductor, like a capacitor. The human body, being a conductor capable of carrying an electric current, generates capacitance when a part of it, such as a fingertip, approaches a touch panel’s surface. This interaction between the body and the sensor’s electrodes allows capacitive touch sensors to support multi-touch gestures with multiple fingers. These sensors are widely used in various products, including smartphones, due to their ability to function on curved surfaces, flexibility, and excellent water resistance.
Uses of Capacitive Touch Sensor
Capacitive touch sensors find extensive use in devices like smartphones, tablets, gaming consoles, ATMs, ticket vending machines, and wearable devices. They serve functions such as detecting if wireless earphones are worn and measuring the remaining liquid in high-precision devices like alcohol dispensers. Kits and modules for capacitive touch sensors are often used as switch modules or film sensors in various applications.
Principle of Capacitive Touch Sensor
Capacitive touch sensors work by detecting changes in capacitance when a conductor, such as a human touch, interacts with sensor electrodes. Indium-Tin Oxide (ITO) electrodes are commonly used in these sensors. The sensor operates by forming a pseudo capacitor between the conductive object and the electric field, registering the capacitance increase as a touch.
1. Self-Capacitance Method
The self-capacitance method involves a single sensor electrode. It is highly sensitive and can function through thick covers. However, this method may mistakenly recognize untouched areas as touch points in multi-touch scenarios, particularly in projection-type setups, which use XY electrode rows or columns for determining touch positions.
2. Mutual-Capacitance Method
The mutual-capacitance method uses separate transmitting and receiving electrodes. It detects touch by noting changes in the electric field between these electrodes when a hand interferes with the field. This method is used in projection-type capacitive touch sensors, which support multi-touch and allow intuitive operations like zooming and pinching.
Types of Capacitive Touch Sensors
1. Surface-Type
Surface-type sensors have electrodes at the substrate’s corners, detecting touch through changes in capacitance on the surface. They are durable, resistant to contaminants, and cost-effective, but do not support multi-touch.
2. Projection-Type
Projection-type sensors, with orthogonally arranged ITO electrodes, detect changes in capacitance at specific coordinates. They are suitable for multi-touch but are more complex and may be susceptible to noise, requiring controller ICs for optimal performance.