Humans are never in direct contact with the sensor, so it can be sealed away from dirt or spillages. There are no moving parts, so there is no wear and tear on the sensor, which is protected by covering material, for example, the plastic cover of an MP3 player. ![]() Q: What are the advantages of capacitive sensing?Ī: Capacitance sensors are more reliable than mechanical sensors-for a number of reasons. No software is required for buttons.įigure 2. For high-resolution sensors such as scroll bars and wheels, the host runs a software algorithm to achieve high resolution output. Software on the host microcontroller to implement the serial interface and the device setup, as well as the interrupt service routine.The traces can be copper, carbon, or silver, while the PCB can be FR4, flex, PET, or ITO. The sensor-a PCB with a pattern of traces, such as buttons, scroll bars, scroll wheels, or some combination.The driver IC, which provides the excitation, the capacitance-to-digital converter, and compensation circuitry to ensure accurate results in all environments.In general, there are three parts to the capacitance-sensing solution, all of which can be supplied by Analog Devices. The resultant decrease in capacitance-on the order of femtofarads as compared to picofarads for the bulk of the electric field-is detected by the converter. The electrical environment changes when a human hand invades the fringe field, with a portion of the electric field being shunted to ground instead of terminating at the receiver. The field strength at the receiver is measured by the on-chip sigma-delta capacitance-to-digital converter. However, a fringe electric field extends from the transmitter, out of the PCB, and terminates back at the receiver. Most of the field is concentrated between the two layers of the sensor PCB. Between the receiver and the transmitter trace, an electric field is formed. As shown in Figure 1, the AD714x has an on-chip excitation source, which is connected to the transmitter trace of the sensor. They provide excitation to the capacitance sensor, sense the changes in capacitance caused by the user’s proximity, and provide a digital output.Ī: A basic sensor includes a receiver and a transmitter, each of which consists of metal traces formed on layers of a printed-circuit board (PCB). The AD7142 and the AD7143, for example, can stimulate and respond to up to 14 and eight capacitance sensors, respectively. Integrated circuits specifically designed to implement capacitance sensing in human-machine interface applications are now available from Analog Devices. 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. Because of their many drawbacks, however, interface designers have been increasingly looking for more reliable solutions. Mechanical buttons, switches, and jog wheels have long been used as the interface between the user and the machine. ![]() A newer application, coming into widespread use, is in human-to-machine interfaces. The technique has been used in industrial applications for many years to measure liquid levels, humidity, and material composition. Ask The Application Engineer-35 Capacitance Sensors for Human Interfaces to Electronic EquipmentĪ: Capacitance sensors detect a change in capacitance when something or someone approaches or touches the sensor.
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