AN2869 datasheet(22/43 Pages) STMICROELECTRONICS

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Surface electrode design

AN2869

22/43

Doc ID 15298 Rev 6

3.4

Rotary sensor

A rotary sensor is a set of contiguous capacitive electrodes (placed in a circle) connected to

the controller pins. It consists of a set of three, five or eight electrodes that can be interlaced,

like the linear touch sensor.

There are three kinds of rotary sensors:

●

Normal patterned rotary sensors

●

Interlaced patterned rotary sensors

●

Rotary sensor with central touchkey

3.4.1

Normal patterned rotary sensor

Figure 15.

Normal patterned rotary sensor (three electrodes)

Legend: d is the diameter of the center, e is the gap between two sensor electrodes, w is the width of the

sensor electrode, L is the length of the external perimeter of the sensor electrode.

The dimensions d, e, w, and L of the three-electrode scheme above can also be applied for

five and eight electrodes, thus giving a bigger rotor.

3.4.2

Interlaced patterned rotary sensors

The three-electrode rotary touch sensor can be used for bigger rotary sensors with an

interlaced pattern.

This allows a smoother transition and a higher sensitivity. To cover a large range of sizes,

more teeth are added inside the rotary touch sensor rather than increasing the size of an

individual tooth.

e <= 0.5 mm

L = 10-12 mm

d >= 5 mm

w = 8-10 mm

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AN2869 데이터시트(PDF) 22 Page - STMicroelectronics