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.