diff --git a/lua_modules/dht22/README.md b/lua_modules/dht22/README.md
index 737c04db..99ea9ff2 100644
--- a/lua_modules/dht22/README.md
+++ b/lua_modules/dht22/README.md
@@ -1,5 +1,8 @@
 # DHT22 module
 
+This module is compatible with DHT22 and DHT21.  
+No need to use a resistor to connect the pin data of DHT22 to ESP8266.
+
 ## Example  
 ```lua
 PIN = 4 --  data pin, GPIO2
@@ -9,14 +12,41 @@ dht22.read(PIN)
 t = dht22.getTemperature()
 h = dht22.getHumidity()
 
--- temperature in degrees Celsius  and Farenheit
-print("Temperature: "..(t/10).."."..(t%10).." deg C")
-print("Temperature: "..(9 * t / 50 + 32).."."..(9 * t / 5 % 10).." deg F")
+if h == -1 then
+  print("Error reading from DHT22")
+else
+  -- temperature in degrees Celsius  and Farenheit
+  print("Temperature: "..(t / 10).."."..(t % 10).." deg C")
+  print("Temperature: "..(9 * t / 50 + 32).."."..(9 * t / 5 % 10).." deg F")
 
--- humidity
-print("Humidity: "..(h/10).."."..(h%10).."%")
+  -- humidity
+  print("Humidity: "..(h/10).."."..(h%10).."%")
+end
 
 -- release module
 dht22 = nil
 package.loaded["dht22"]=nil
 ```
+## Functions
+### read
+read(pin) 
+Read humidity and temperature from DHT22.
+
+**Parameters:**
+
+* pin - ESP8266 pin connect to data pin in DHT22
+
+### getHumidity
+getHumidity()  
+Returns the humidity of the last reading.
+
+**Returns:**  
+* last humidity reading in per thousand
+
+### getTemperature
+getTemperature()  
+Returns the temperature of the last reading.
+
+**Returns:**  
+* last temperature reading in 0.1ºC
+
diff --git a/lua_modules/dht22/dht22.lua b/lua_modules/dht22/dht22.lua
index 9d44c8b8..d2374050 100644
--- a/lua_modules/dht22/dht22.lua
+++ b/lua_modules/dht22/dht22.lua
@@ -13,23 +13,22 @@ _G[moduleName] = M
 
 local humidity
 local temperature
-local checksum
-local checksumTest
 
 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
-  gpio_read = gpio.read
-  gpio_write = gpio.write
+  local gpio_read = gpio.read
   
-  bitStream = {}
+  local bitStream = {}
   for j = 1, 40, 1 do
     bitStream[j] = 0
   end
-  bitlength = 0
+  local bitlength = 0
 
   -- Step 1:  send out start signal to DHT22
   gpio.mode(pin, gpio.OUTPUT)
@@ -43,13 +42,13 @@ function M.read(pin)
   -- Step 2:  DHT22 send response signal 
   -- 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
+  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 < 100) do c = c + 1 end
-
+  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
@@ -63,17 +62,17 @@ function M.read(pin)
 
   --DHT data acquired, process.
   for i = 1, 16, 1 do
-    if (bitStream[i + 0] > 2) then
+    if (bitStream[i] > 4) then
       humidity = humidity + 2 ^ (16 - i)
     end
   end
   for i = 1, 16, 1 do
-    if (bitStream[i + 16] > 2) then
+    if (bitStream[i + 16] > 4) then
       temperature = temperature + 2 ^ (16 - i)
     end
   end
   for i = 1, 8, 1 do
-    if (bitStream[i + 32] > 2) then
+    if (bitStream[i + 32] > 4) then
       checksum = checksum + 2 ^ (8 - i)
     end
   end