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AN4312

Surface sensor design

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3.4

Rotary sensor

A rotary sensor is a set of contiguous capacitive electrodes connected to the device and

placed in a circular way. The number of electrodes depends on the size and the resolution of

the sensor.

The electrodes can be arranged in two ways:

•

mono electrode design (same as the half-ended electrode design)

•

dual electrode design.

Like for the linear sensor, there are two options for designing the electrode pattern on the

PCB:

•

normal pattern

•

interlaced pattern.

These two patterns are described in more details below.

A rotary sensor can also have a touchkey placed in the center.

3.4.1

Normal patterned rotary sensor

Figure 18. Normal patterned rotary sensor with 3 channels / 3 electrodes

1. 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.

e <= 0.5 mm

L = 10-12 mm

d >= 5 mm

w = 8-10 mm

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