DHT22 module

lua_modules/dht22/dht22.lua

@@ -0,0 +1,101 @@
+-- ***************************************************************************
+-- DHT22 module for ESP8266 with nodeMCU
+--
+-- 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
+local checksum
+local checksumTest
+
+function M.read(pin)
+  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
+  
+  bitStream = {}
+  for j = 1, 40, 1 do
+    bitStream[j] = 0
+  end
+  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
+  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
+
+  -- 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
+
+  --DHT data acquired, process.
+  for i = 1, 16, 1 do
+    if (bitStream[i + 0] > 2) then
+      humidity = humidity + 2 ^ (16 - i)
+    end
+  end
+  for i = 1, 16, 1 do
+    if (bitStream[i + 16] > 2) then
+      temperature = temperature + 2 ^ (16 - i)
+    end
+  end
+  for i = 1, 8, 1 do
+    if (bitStream[i + 32] > 2) then
+      checksum = checksum + 2 ^ (8 - i)
+    end
+  end
+
+  checksumTest=((humidity / 256) + (humidity % 256) + (temperature / 256) + (temperature % 256)) % 256
+
+  if temperature > 0x8000 then
+    -- convert to negative format
+    temperature = -(temperature - 0x8000)
+  end
+
+  if checksum ~= checksumTest then
+    humidity = -1
+  end
+end
+
+function M.getTemperature()
+  return temperature
+end
+
+function M.getHumidity()
+  return humidity
+end
+
+return M