nodemcu-firmware/lua_examples/adc_rgb.lua

--
-- Light sensor on ADC(0), RGB LED connected to gpio12(6) Green, gpio13(7) Blue & gpio15(8) Red.
-- This works out of the box on the typical ESP8266 evaluation boards with Battery Holder
--
-- It uses the input from the sensor to drive a "rainbow" effect on the RGB LED
-- Includes a very "pseudoSin" function
--

function led(r,Sg,b)
    pwm.setduty(8,r)
    pwm.setduty(6,g)
    pwm.setduty(7,b)
end

-- this is perhaps the lightest weight sin function in existance
-- Given an integer from 0..128, 0..512 appximating 256 + 256 * sin(idx*Pi/256)
-- This is first order square approximation of sin, it's accurate around 0 and any multiple of 128 (Pi/2),
--  92% accurate at 64 (Pi/4).
function pseudoSin (idx)
    idx = idx % 128
    lookUp = 32 - idx % 64
    val = 256 - (lookUp * lookUp) / 4
    if (idx > 64) then
        val = - val;
    end
    return 256+val
end

pwm.setup(6,500,512)
pwm.setup(7,500,512)
pwm.setup(8,500,512)
pwm.start(6)
pwm.start(7)
pwm.start(8)

tmr.alarm(1,20,1,function()
	idx = 3 * adc.read(0) / 2
  r = pseudoSin(idx)
  g = pseudoSin(idx + 43)
  b = pseudoSin(idx + 85)
	led(r,g,b)
	idx = (idx + 1) % 128
	end)