EIT week35 Capacitive Touch Sensing

Capacitive Touch Sensing

Overview

• Topic: Capacitive Touch Sensing
• Context: Engineering Interaction Technologies
• Professor: Michael Wessely, Interactive Matter Lab

Sensing Principle

• Capacitive Sensing: Relies on the change in capacitance when a conductive object (like a finger) approaches or touches the sensor.
  • Formula for Capacitance: \(\begin{equation} C = \epsilon \left(\frac{A}{d}\right) \label{eq:capacitance} \end{equation}\)
    • ( A ) = overlapping area between two electrodes
    • ( d ) = distance between the electrodes

Applications

• Movement and Touch:
  • Buttons, sliders, dials, multi-touch pads
  • Sensing proximity, folding, rotation, linear elongation, shear, and pressure

Sensing Mechanics

• Capacitance Change Factors:
  • Overlapping area increases as the finger covers more of the touch button, increasing capacitance.
  • Decreased distance between electrodes when touched, raising capacitance.

User Influence

• Capacitance Dependency:
  • Size of the user’s finger affects the overlapping area.
  • Touch button design influences the amount of overlap and, consequently, capacitance.
  • Environmental conditions such as air humidity can affect the dielectric properties between electrodes, influencing capacitance.
  • The user’s connection to the ground, influenced by factors such as shoes, also impacts capacitance.

Design Insights

• Button Design: Discrete vs. Continuous
  • Discrete sliders consist of segmented touch buttons with no overlap, while continuous sliders allow overlapping touches, enabling the detection of gradual movements.

Lecture Focus

• Lab Tasks:
  • Designing circuits for touch sensing
  • Creating user interfaces that utilize capacitive sensing for various controls like sliders and dials.