101 lines
2.4 KiB
Lua
101 lines
2.4 KiB
Lua
-- ***************************************************************************
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-- DHT22 module for ESP8266 with nodeMCU
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--
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-- Written by Javier Yanez
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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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local moduleName = ...
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local M = {}
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_G[moduleName] = M
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local humidity
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local temperature
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function M.read(pin)
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local checksum
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local checksumTest
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humidity = 0
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temperature = 0
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checksum = 0
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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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local bitStream = {}
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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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local bitlength = 0
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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: DHT22 send response signal
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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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--DHT data acquired, process.
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for i = 1, 16, 1 do
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if (bitStream[i] > 4) 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] > 4) 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] > 4) 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=((humidity / 256) + (humidity % 256) + (temperature / 256) + (temperature % 256)) % 256
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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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if checksum ~= checksumTest then
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humidity = -1
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end
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end
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function M.getTemperature()
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return temperature
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end
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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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