
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I 73
Influence of diameter on FTC
Figure 8-3. FTC versus Spring Diameter
0
0,5
1
1,5
2
2,5
3
0 5 10 15 20 25
Diameter of the Spring, mm
Introduced Capacitance, pF
Influence of wire thickness of the spring on FTC
Figure 8-4. FTC versus Wire Thickness of Spring
0,52
0,53
0,54
0,55
0,56
0,57
0,58
0,59
0 1 2 3 4 5 6
Wire Thickness of the Spring, mm
Introduced Capacitance, pF
8.1.2 Mounting Springs to the PCB
Figure 8-5 shows an example of spring mounting. This section discusses how to design spring sensors. Because
springs have higher side sensitivity, the neighboring spring sensors must be placed as far as possible from each
other to prevent false detections. Add a comparison level if the sensor pitch is small.
The requirements for the sensitive area of a spring are the same as the requirements for solid buttons. When using
thick overlays, the spring diameter must be larger than the overlay thickness by at least 2 or 3 times. The distance
between the PCB and the overlay must be 5 mm or more.
Figure 8-5. Spring Mounting Example
PCB
Metal Spring
Trace to PSoC
Solder
VIA
Overlay
VIA
Solder point
Copper Ring
Trace to
PSoC
Metal Spring
PCB
LED for
BackLighting
VIA
Sensing
Area
Copper-free
area
> 5 mm
Overlay
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