Capacitance Sensors for Human Interfaces to Electronic Equipment：A: Capacitance sensors detect a change in capacitance when
something or someone approaches or touches the sensor. The
technique has been used in industrial applications for many years
to measure liquid levels, humidity, and material composition.
A newer application, coming into widespread use, is in humanto-
machine interfaces. Mechanical buttons, switches, and jog
wheels have long been used as the interface between the user
and the machine. Because of their many drawbacks, however,
interface designers have been increasingly looking for more
reliable solutions. Capacitive sensors can be used in the same
manner as buttons, but they also can function with greater
versatility, for example, when implementing a 128-position
scroll bar.
Integrated circuits specifically designed to implement
capacitance sensing in human-machine interface applications
are now available from Analog Devices. The AD71421 and the
AD7143, for example, can stimulate and respond to up to 14 and
eight capacitance sensors, respectively. They provide excitation
to the capacitance sensor, sense the changes in capacitance
caused by the user’s proximity, and provide a digital output.