air101

This chapter describes how to use the pwm library for LuatOS

Introduction

Pulse width modulation (PWM), is the English “Pulse Width Modulation” abbreviation, referred to as pulse width modulation, is the use of microprocessor digital output to control the analog circuit of a very effective technology. Simply, it is the control of pulse width.

Looking up air101_chip specification_v1.1.pdf, it can be seen that Air101 has 5 PWM channels, the frequency range is 3Hz-160kHz, and the maximum accuracy of duty cycle is 1/256

We can adjust the brightness of the LED small light by pwm different duty cycle output

Hardware preparation

• Air101 Development Board

• LED small lamp

Wiring Schematic

        PWM0  ------  +  
Air101                     LED
        GND   ------  -

Software part

Interface documentation can be referred to:pwm library

Turn on pwm output

Turn on the pwm output of the PWM0 channel, set different duty cycles, the small lights will have different brightness

PROJECT = "pwm"
VERSION = "1.0.0"

sys = require("sys")

sys.taskInit(function()
    while true do
        -- Turn on pwm channel 0, set the pulse frequency to 1kHz, the frequency division accuracy to 100, and the duty cycle to 100 = 10% continuous output
        pwm.open(0, 1000, 10, 0, 100) -- The small lamp glows slightly
        sys.wait(1000)
        -- Turn on pwm channel 0, set the pulse frequency to 1kHz, the frequency division accuracy to 100, and the duty cycle to 50/100 = 50% continuous output
        pwm.open(0, 1000, 50, 0, 100) -- Small light medium brightness
        sys.wait(1000)
        -- Turn on pwm channel 0, set the pulse frequency to 1kHz, the frequency division accuracy to 100, and the duty cycle to 100/100=100 continuous output
        pwm.open(0, 1000, 100, 0, 100) -- Small lamp with high brightness
        sys.wait(1000)
    end
end)

sys.run()

Breathing light effect

The effect of breathing light is the effect that the small lamp is lit up little by little and extinguished little by little when it is never lit. We can continuously increase the duty cycle to make the small lamp light up little by little and then continuously decrease the duty cycle to make the small lamp extinguish little by little.

The code is as follows

PROJECT = "pwm"
VERSION = "1.0.0"

sys = require("sys")

sys.taskInit(function()
    while true do
        -- The duty cycle continuously improves the brightness of small lamps from 0% to 50%
        for i = 0, 50 do
            pwm.open(0, 1000, i, 0, 100)
            sys.wait(10)
        end
        sys.wait(1000)
        -- Duty cycle continuously reduces the brightness of small lamps from 50% to 0%
        for i = 50, 0, -1 do
            pwm.open(0, 1000, i, 0, 100)
            sys.wait(10)
        end
        sys.wait(1000)
    end
end)

sys.run()