dht11.lua

-- Measure temperature, humidity and return the values as a string.
-- Based on DHT11 code from esp8266.com

local dht11 = {}

local pin = 4
local Humidity = 0
local HumidityDec=0
local Temperature = 0
local TemperatureDec=0
local Checksum = 0
local ChecksumTest=0


function dht11.getData()
    Humidity = 0
    HumidityDec = 0
    Temperature = 0
    TemperatureDec = 0
    Checksum = 0
    ChecksumTest = 0
    
    --Data stream acquisition timing is critical. There's
    --barely enough speed to work with to make this happen.
    --Pre-allocate vars used in loop.
    
    bitStream = {}
    for j = 1, 40, 1 do
         bitStream[j]=0
    end
    bitlength=0
    
    gpio.mode(pin, gpio.OUTPUT)
    gpio.write(pin, gpio.LOW)
    tmr.delay(20000)
    --Use Markus Gritsch trick to speed up read/write on GPIO
    gpio_read=gpio.read
    gpio_write=gpio.write
    
    gpio.mode(pin, gpio.INPUT)
    
    --bus will always let up eventually, don't bother with timeout
    while (gpio_read(pin)==0 ) do end
    
    c=0
    while (gpio_read(pin)==1 and c<100) do c=c+1 end
    
    --bus will always let up eventually, don't bother with timeout
    while (gpio_read(pin)==0 ) do end
    
    c=0
    while (gpio_read(pin)==1 and c<100) do c=c+1 end
    
    --acquisition loop
    for j = 1, 40, 1 do
         while (gpio_read(pin)==1 and bitlength<10 ) do
              bitlength=bitlength+1
         end
         bitStream[j]=bitlength
         bitlength=0
         --bus will always let up eventually, don't bother with timeout
         while (gpio_read(pin)==0) do end
    end
    
    --DHT data acquired, process.
    
    for i = 1, 8, 1 do
         if (bitStream[i+0] > 2) then
              Humidity = Humidity+2^(8-i)
         end
    end
    for i = 1, 8, 1 do
         if (bitStream[i+8] > 2) then
              HumidityDec = HumidityDec+2^(8-i)
         end
    end
    for i = 1, 8, 1 do
         if (bitStream[i+16] > 2) then
              Temperature = Temperature+2^(8-i)
         end
    end
    for i = 1, 8, 1 do
         if (bitStream[i+24] > 2) then
              TemperatureDec = TemperatureDec+2^(8-i)
         end
    end
    for i = 1, 8, 1 do
         if (bitStream[i+32] > 2) then
              Checksum = Checksum+2^(8-i)
         end
    end
    ChecksumTest=(Humidity+HumidityDec+Temperature+TemperatureDec) % 0xFF
    
    return  Temperature.."."..TemperatureDec..";"..Humidity.."."..HumidityDec

end

return dht11