Capacitive Touch on AVR® using the PTC

The Peripheral Touch Controller (PTC), in some AVR® devices, is used for capacitive touch applications. The PTC acquires signals in order to detect a touch on capacitive sensors. The external capacitive touch sensor is typically formed on a PCB, and the sensor electrodes are connected to the analog front end of the PTC through the I/O pins in the device. The PTC supports both self- and mutual-capacitance sensors.

I/O Connections.

The I/O lines used for analog X-lines and Y-lines must be connected to external capacitive touch sensor electrodes. External components are not required for normal operation. However, to improve the Electromagnetic Compatibility (EMC) performance, a series resistor of 1k Ω or more can be used on X-lines and Y-lines.

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Mutual-Capacitance Mode

In the mutual-capacitance mode, sensing is done using capacitive touch matrices in various X-Y configurations, including indium tin oxide (ITO) sensor grids. The PTC requires one pin per X-line and one pin per Y-line. A mutual-capacitance sensor is formed between the two I/O lines - an X electrode for transmitting and Y electrode for sensing. The mutual capacitance between the X and Y electrode is measured by the PTC.

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Self-Capacitance Mode

In the self-capacitance mode, the PTC requires only one pin (Y-line) for each touch sensor. A self-capacitance sensor is connected to a single pin on the PTC through the Y electrode for sensing the signal. The sense electrode capacitance is measured by the PTC.

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Additional Information

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