105 lines
2.1 KiB
Lua
105 lines
2.1 KiB
Lua
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-- ***************************************************************************
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-- SI7021 module for ESP8266 with nodeMCU
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-- Si7021 compatible tested 2015-1-22
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--
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-- Written by VIP6
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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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--I2C slave address of Si70xx
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local Si7021_ADDR = 0x40
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--Commands
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local CMD_MEASURE_HUMIDITY_HOLD = 0xE5
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local CMD_MEASURE_HUMIDITY_NO_HOLD = 0xF5
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local CMD_MEASURE_TEMPERATURE_HOLD = 0xE3
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local CMD_MEASURE_TEMPERATURE_NO_HOLD = 0xF3
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-- temperature and pressure
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local t,h
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local init = false
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-- i2c interface ID
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local id = 0
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-- 16-bit two's complement
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-- value: 16-bit integer
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local function twoCompl(value)
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if value > 32767 then value = -(65535 - value + 1)
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end
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return value
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end
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-- read data from si7021
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-- ADDR: slave address
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-- commands: Commands of si7021
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-- length: bytes to read
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local function read_data(ADDR, commands, length)
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i2c.start(id)
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i2c.address(id, ADDR, i2c.TRANSMITTER)
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i2c.write(id, commands)
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i2c.stop(id)
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i2c.start(id)
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i2c.address(id, ADDR,i2c.RECEIVER)
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tmr.delay(20000)
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c = i2c.read(id, length)
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i2c.stop(id)
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return c
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end
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-- initialize module
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-- sda: SDA pin
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-- scl SCL pin
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function M.init(sda, scl)
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i2c.setup(id, sda, scl, i2c.SLOW)
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--print("i2c ok..")
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init = true
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end
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-- read humidity from si7021
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local function read_humi()
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dataH = read_data(Si7021_ADDR, CMD_MEASURE_HUMIDITY_HOLD, 2)
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UH = string.byte(dataH, 1) * 256 + string.byte(dataH, 2)
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h = ((UH*12500+65536/2)/65536 - 600)
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return(h)
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end
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-- read temperature from si7021
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local function read_temp()
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dataT = read_data(Si7021_ADDR, CMD_MEASURE_TEMPERATURE_HOLD, 2)
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UT = string.byte(dataT, 1) * 256 + string.byte(dataT, 2)
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t = ((UT*17572+65536/2)/65536 - 4685)
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return(t)
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end
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-- read temperature and humidity from si7021
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function M.read()
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if (not init) then
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print("init() must be called before read.")
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else
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read_humi()
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read_temp()
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end
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end;
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-- get humidity
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function M.getHumidity()
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return h
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end
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-- get temperature
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function M.getTemperature()
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return t
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end
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return M
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