
26 Document No. 001-64846 Rev. *I Getting Started with CapSense
®
2.7.1.1.4 LED Fading
By gradually changing the duty cycle between LED states, you can achieve a fading effect (see Figure 2-23). For
example, the LED appears to ―fade in‖ (from OFF to ON) when the duty cycle is increased in a series of small steps.
Figure 2-23. LED Fading
2.7.1.1.5 LED Breathing
Gradually increasing and decreasing the duty cycle between two levels on a continuous basis makes the LED appear
to ―breathe‖, as shown in Figure 2-24. LED breathing is useful when a system is in idle or stand-by mode. For
example, a power button can appear to breathe to alert the user that it is active and can be operated.
Figure 2-24. LED Breathing
100%
OFFON OFF
t
LED Brightness
ON
Human Eye Sensitivity
The human eye‘s sensitivity to the brightness of a light source looks similar to a logarithmic function (Figure 2-25). To
provide a visible linear brightness change, change the PWM duty cycle in an exponential manner.
Figure 2-25. Human Eye Brightness Perception versus LED Luminous Flux
Light Source
Brightness
Visible
Brightness
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