User guide

22 Document No. 001-64846 Rev. *A 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 as shown in Figure 2-22.
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 2-22. 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 2-23. 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 2-23. LED Breathing
Human Eye Sensitivity
The human eye’s sensitivity to the brightness of a light source looks similar to a logarithmic function (Figure 2-24). To
provide a visible linear brightness change, the PWM duty cycle should be changed in an exponential way.
Figure 2-24. Human Eye Brightness Perception versus LED Luminous Flux
Light Source
Brightness
Visible
Brightness