-- *************************************************************************** -- for communication of DHT sensor only -- DHT module for ESP8266 with nodeMCU floating point -- Written by Javier Yanez -- but based on a script of Pigs Fly from ESP8266.com forum -- MIT license, http://opensource.org/licenses/MIT -- *************************************************************************** local moduleName = ... local M = {} _G[moduleName] = M local humidity local temperature function M.read(pin) local checksum local checksumTest humidity = 0 temperature = 0 checksum = 0 -- Use Markus Gritsch trick to speed up read/write on GPIO local gpio_read = gpio.read local bitStream = {} for j = 1, 40, 1 do bitStream[j] = 0 end local bitlength = 0 -- Step 1: send out start signal to DHT22 gpio.mode(pin, gpio.OUTPUT) gpio.write(pin, gpio.HIGH) tmr.delay(100) gpio.write(pin, gpio.LOW) tmr.delay(20000) gpio.write(pin, gpio.HIGH) gpio.mode(pin, gpio.INPUT) -- Step 2: DHT22 send response signal -- bus will always let up eventually, don't bother with timeout while (gpio_read(pin) == 0 ) do end local c=0 while (gpio_read(pin) == 1 and c < 500) 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 < 500) do c = c + 1 end -- Step 3: DHT22 send data 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 hum=" " tem=" " chk=" " --DHT data acquired, process. for i = 1, 16, 1 do hum=hum.." "..tostring(bitStream[i]) tem=tem.." "..tostring(bitStream[i+16]) if (bitStream[i] > 3) then humidity = humidity + 2 ^ (16 - i) end if (bitStream[i + 16] > 3) then temperature = temperature + 2 ^ (16 - i) end end for i = 1, 8, 1 do chk=chk.." "..tostring(bitStream[i+32]) if (bitStream[i + 32] > 3) then checksum = checksum + 2 ^ (8 - i) end end checksumTest = (bit.band(humidity, 0xFF) + bit.rshift(humidity, 8) + bit.band(temperature, 0xFF) + bit.rshift(temperature, 8)) checksumTest = bit.band(checksumTest, 0xFF) if temperature > 0x8000 then -- convert to negative format temperature = -(temperature - 0x8000) end -- conditions compatible con float point and integer if (checksumTest - checksum >= 1) or (checksum - checksumTest >= 1) then humidity = nil end --print("checksum ", checksum) --print("checksumTest ", checksumTest) --print("humidity - timing of bits ",hum) --print("temperat - timing of bits ",tem) --print("checksum - timing of bits ",chk) end function M.getTemperature() return temperature end function M.getHumidity() return humidity end return M