Cypress CapSense CY8C20x36 Guide de l'utilisateur télécharger pdf (Page 26)

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

100%

LED

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

LED Brightness

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

1 2 ... 21 22 23 24 25 26 27 28 29 30 31 ... 74 75

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Cypress CapSense CY8C20x36 Guide de l'utilisateur Page 26