Velleman VMP502, Руководство пользователя

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VMP502
V. 02
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25/10/2019 12 ©Velleman nv
Python Programming
6.4 Breathing LED
We will gradually increase and decrease the luminance of an LED with PWM.
Required Hardware
•
1 x Raspberry Pi
®
•
1 x breadboard
•
1 x LED
•
1 x 220
Ω resistor
•
jumper wires as needed
Pulse Width Modulation
–
or PWM
–
is a technique for getting analogue results with digital means. Digital
control is used to create a square wave, a signal switched between on and off. This on-off pattern can simulate
voltages between full on (3.3 V) and off (0 V) by changing the portion of the time the signal spends on versus
the time t
hat the signal spends off. The duration of the “on time” is called the pulse width. To get varying
analogue values, you change
–
or modulate
–
that pulse width. If you repeat this on-off pattern fast enough
with an LED, the result is as if the signal is a steady voltage between 0 and 3.3 V controlling the brightness of
the LED.
A duty cycle is the percentage of one period in which a signal is active. A period is a time it takes for a signal to
complete an on-off cycle. As a formula, a duty cycle may be expressed as: