Add support to DHT11 and add some comments.
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Martin Han
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# DHTxx module
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-- ***************************************************************************
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-- DHTxx(11,21,22) module for ESP8266 with nodeMCU
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--
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-- Written by Javier Yanez mod by Martin
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-- but based on a script of Pigs Fly from ESP8266.com forum
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--
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-- MIT license, http://opensource.org/licenses/MIT
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-- ***************************************************************************
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This module is compatible with DHT11, DHT21 and DHT22.
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And is able to auto-select wheather you are using DHT11 or DHT2x
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--Support list：
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--DHT11 Tested ->read11
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--DHT21 Not Tested->read22
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--DHT22 Tested->read22
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No need to use a resistor to connect the pin data of DHT22 to ESP8266.
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--==========================Module Part======================
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local moduleName = ...
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local M = {}
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_G[moduleName] = M
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--==========================Local the UMI and TEMP===========
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local humidity
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local temperature
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--==========================Local the bitStream==============
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local bitStream = {}
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##Integer Verison[When using DHT11, Float version is useless...]
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### Example
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```lua
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PIN = 4 -- data pin, GPIO2
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---------------------------Read bitStream from DHTXX--------------------------
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local function read(pin)
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DHT= require("dht_lib")
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local bitlength = 0
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humidity = 0
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temperature = 0
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DHT.read(PIN)
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t = DHT.getTemperature()
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h = DHT.getHumidity()
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if h == nil then
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print("Error reading from DHTxx")
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else
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-- temperature in degrees Celsius and Farenheit
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print("Temperature: "..((t-(t % 10)) / 10).."."..(t % 10).." deg C")
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print("Temperature: "..(9 * t / 50 + 32).."."..(9 * t / 5 % 10).." deg F")
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-- Use Markus Gritsch trick to speed up read/write on GPIO
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local gpio_read = gpio.read
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-- humidity
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for j = 1, 40, 1 do
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bitStream[j] = 0
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end
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print("Humidity: "..((h - (h % 10)) / 10).."."..(h % 10).."%")
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-- Step 1: send out start signal to DHT22
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gpio.mode(pin, gpio.OUTPUT)
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gpio.write(pin, gpio.HIGH)
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tmr.delay(100)
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gpio.write(pin, gpio.LOW)
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tmr.delay(20000)
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gpio.write(pin, gpio.HIGH)
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gpio.mode(pin, gpio.INPUT)
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-- Step 2: Receive bitStream from DHT11/22
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-- bus will always let up eventually, don't bother with timeout
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while (gpio_read(pin) == 0 ) do end
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local c=0
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while (gpio_read(pin) == 1 and c < 500) do c = c + 1 end
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-- bus will always let up eventually, don't bother with timeout
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while (gpio_read(pin) == 0 ) do end
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c=0
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while (gpio_read(pin) == 1 and c < 500) do c = c + 1 end
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-- Step 3: DHT22 send data
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for j = 1, 40, 1 do
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while (gpio_read(pin) == 1 and bitlength < 10 ) do
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bitlength = bitlength + 1
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end
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bitStream[j] = bitlength
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bitlength = 0
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-- bus will always let up eventually, don't bother with timeout
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while (gpio_read(pin) == 0) do end
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end
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end
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---------------------------Convert the bitStream into Number through DHT11 Ways--------------------------
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local function bit2DHT11()
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--As for DHT11 40Bit is consisit of 5Bytes
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--First byte->Humidity Data's Int part
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--Sencond byte->Humidity Data's Float Part(Which should be empty)
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--Third byte->Temp Data;s Intpart
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--Forth byte->Temp Data's Float Part(Which should be empty)
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--Fifth byte->SUM Byte, Humi+Temp
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local checksum = 0
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local checksumTest
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--DHT data acquired, process.
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for i = 1, 8, 1 do -- Byte[0]
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if (bitStream[i] > 3) then
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humidity = humidity + 2 ^ (8 - i)
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end
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end
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for i = 1, 8, 1 do -- Byte[2]
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if (bitStream[i + 16] > 3) then
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temperature = temperature + 2 ^ (8 - i)
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end
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end
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for i = 1, 8, 1 do --Byte[4]
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if (bitStream[i + 32] > 3) then
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checksum = checksum + 2 ^ (8 - i)
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end
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end
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if(checksum ~= humidity+temperature) then
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humidity = nil
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temperature = nil
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end
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end
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---------------------------Convert the bitStream into Number through DHT22 Ways--------------------------
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local function bit2DHT22()
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--As for DHT22 40Bit is consisit of 5Bytes
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--First byte->Humidity Data's High Bit
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--Sencond byte->Humidity Data's Low Bit(And if over 0x8000, use complement)
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--Third byte->Temp Data's High Bit
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--Forth byte->Temp Data's Low Bit
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--Fifth byte->SUM Byte
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local checksum = 0
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local checksumTest
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--DHT data acquired, process.
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for i = 1, 16, 1 do
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if (bitStream[i] > 3) then
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humidity = humidity + 2 ^ (16 - i)
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end
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end
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for i = 1, 16, 1 do
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if (bitStream[i + 16] > 3) then
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temperature = temperature + 2 ^ (16 - i)
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end
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end
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for i = 1, 8, 1 do
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if (bitStream[i + 32] > 3) then
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checksum = checksum + 2 ^ (8 - i)
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end
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end
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checksumTest = (bit.band(humidity, 0xFF) + bit.rshift(humidity, 8) + bit.band(temperature, 0xFF) + bit.rshift(temperature, 8))
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checksumTest = bit.band(checksumTest, 0xFF)
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if temperature > 0x8000 then
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-- convert to negative format
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temperature = -(temperature - 0x8000)
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end
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-- conditions compatible con float point and integer
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if (checksumTest - checksum >= 1) or (checksum - checksumTest >= 1) then
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humidity = nil
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end
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end
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-- release module
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DHT = nil
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package.loaded["dht_lib"]=nil
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```
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##Float Verison
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###Example
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```lua
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PIN = 4 -- data pin, GPIO2
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---------------------------Check out the data--------------------------
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----Auto Select the DHT11/DHT22 By check the byte[1] && byte[3]AND ---
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---------------Which is empty when using DHT11-------------------------
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function M.read(pin)
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DHT= require("dht_lib")
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read(pin)
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DHT.read(PIN)
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local byte_1 = 0
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local byte_2 = 0
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t = DHT.getTemperature()
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h = DHT.getHumidity()
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for i = 1, 8, 1 do -- Byte[1]
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if (bitStream[i+8] > 3) then
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byte_1 = byte_1 + 2 ^ (8 - i)
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end
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end
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if h == nil then
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print("Error reading from DHT11/22")
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else
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-- temperature in degrees Celsius and Farenheit
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-- floating point and integer version:
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for i = 1, 8, 1 do -- Byte[1]
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if (bitStream[i+24] > 3) then
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byte_2 = byte_2 + 2 ^ (8 - i)
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end
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end
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if byte_1==0 and byte_2 == 0 then
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bit2DHT11()
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else
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bit2DHT22()
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end
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print("Temperature: "..(t/10).." deg C")
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print("Temperature: "..(9 * t / 50 + 32).." deg F")
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-- humidity
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print("Humidity: "..(h/10).."%")
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end
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-- release module
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DHT = nil
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package.loaded["dht_lib"]=nil
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```
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## Functions
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###read
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read(pin)
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Read humidity and temperature from DHTxx(11,21,22...).
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**Parameters:**
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function M.getTemperature()
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return temperature
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end
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* pin - ESP8266 pin connect to data pin
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### getHumidity
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getHumidity()
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Returns the humidity of the last reading.
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**Returns:**
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* last humidity reading in per thousand
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### getTemperature
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getTemperature()
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Returns the temperature of the last reading.
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**Returns:**
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* last temperature reading in(dht22) 0.1ºC (dht11)1ºC
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*
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function M.getHumidity()
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return humidity
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end
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return M
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