- Sun Feb 01, 2015 4:40 pm
#8729
Having just begun to *play* with this module (WI07c from Electrodragon), this was my first demo with a DHT11. As the LUA code stood, it would not read properly evident from the continuous check sum errors. Now, I'm not a programmer at all and I only heard of LUA a week days ago but I had to modify the minimum count for it to read correctly. I also removed a couple of lines that didn't appear to make sense to me. Again, not a programmer but my unit is working. Here is my modified dht.lua code in case it helps others.
Code: Select all
-- ***************************************************************************
-- DHT22/11 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
local minCountForLow = 1
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 DHT
gpio.mode(pin, gpio.OUTPUT)
--MCU needs to pull data line down >18mS to signal DHT response
gpio.write(pin, gpio.LOW)
tmr.delay(20000)
--MCU awaiting response
gpio.mode(pin, gpio.INPUT)
-- Step 2: DHT send response signal
-- MCU looks for DHT to respond with 80uS low on the data line
while (gpio_read(pin) == 0 ) do end
-- Followed by a 80uS high on the data line
while (gpio_read(pin) == 1) do end
-- MCU looks for DHT to indicate start bit by pulling data line down for 50uS
while (gpio_read(pin) == 0 ) do end
-- Step 3: DHT send data (40 bits)
for j = 1, 40, 1 do
while (gpio_read(pin) == 1 and bitlength < 3 ) do
bitlength = bitlength + 1
end
bitStream[j] = bitlength
bitlength = 0
-- MCU looks for DHT to indicate start of next bit by pulling data line down for 50uS
while (gpio_read(pin) == 0) do end
end
--DHT data acquired, process.
for i = 1, 16, 1 do
if (bitStream[i + 0] > minCountForLow) then
-- Add up all the "high" bit postion values
humidity = humidity + 2 ^ (16 - i)
end
if (bitStream[i + 16] > minCountForLow) then
-- Add up all the "high" bit postion values
temperature = temperature + 2 ^ (16 - i)
end
end
for i = 1, 8, 1 do
if (bitStream[i + 32] > minCountForLow) then
-- Add up all the "high" bit postion values
checksum = checksum + 2 ^ (8 - i)
end
end
checksumTest=((humidity-humidity%256)/256+humidity%256+(temperature-temperature%256)/256+temperature%256)%256
if temperature > 0x8000 then
-- convert to negative format
temperature = -(temperature - 0x8000)
end
if tostring(checksum) ~= tostring(checksumTest) then
humidity = -1
end
end
function M.getTemperature()
return temperature
end
function M.getHumidity()
return humidity
end
return M
