nodemcu-firmware/modules/bmp085.lua

--------------------------------------------------------------------------------
-- BMP085 I2C module for NODEMCU
-- NODEMCU TEAM
-- LICENCE: http://opensource.org/licenses/MIT
-- Christee <Christee@nodemcu.com>
--------------------------------------------------------------------------------
    local moduleName = ... 
    local M = {}
    _G[moduleName] = M
  
    --default value for i2c communication
    local id=0

    --default oversampling setting
    local oss = 0
    
    --CO: calibration coefficients table.
    local CO = {}

    -- read reg for 1 byte
    local function read_reg(dev_addr, reg_addr)
      i2c.start(id)
      i2c.address(id, dev_addr ,i2c.TRANSMITTER)
      i2c.write(id,reg_addr)
      i2c.stop(id)
      i2c.start(id)
      i2c.address(id, dev_addr,i2c.RECEIVER)
      local c=i2c.read(id,1)
      i2c.stop(id)
      return c
    end   

    --write reg for 1 byte
    local function write_reg(dev_addr, reg_addr, reg_val)
      i2c.start(id)
      i2c.address(id, dev_addr, i2c.TRANSMITTER)
      i2c.write(id, reg_addr)
      i2c.write(id, reg_val)
      i2c.stop(id)
    end    

    --get signed or unsigned 16
    --parameters:
    --reg_addr: start address of short
    --signed: if true, return signed16
    local function getShort(reg_addr, signed)
      local tH = string.byte(read_reg(0x77, reg_addr))
      local tL = string.byte(read_reg(0x77, (reg_addr + 1)))
      local temp = tH*256 + tL
      if (temp > 32767) and (signed == true) then 
        temp = temp - 65536
      end
      return temp
    end    

    -- initialize i2c
    --parameters:
    --d: sda
    --l: scl
    function M.init(d, l)      
      if (d ~= nil) and (l ~= nil) and (d >= 0) and (d <= 11) and (l >= 0) and ( l <= 11) and (d ~= l) then
        sda = d
        scl = l 
      else 
        print("iic config failed!") return nil
      end
        print("init done")
        i2c.setup(id, sda, scl, i2c.SLOW) 
        --get calibration coefficients.
        CO.AC1 = getShort(0xAA, true)
        CO.AC2 = getShort(0xAC, true)
        CO.AC3 = getShort(0xAE, true)
        CO.AC4 = getShort(0xB0)         
        CO.AC5 = getShort(0xB2)
        CO.AC6 = getShort(0xB4)
        CO.B1  = getShort(0xB6, true)
        CO.B2  = getShort(0xB8, true)
        CO.MB  = getShort(0xBA, true)
        CO.MC  = getShort(0xBC, true)
        CO.MD  = getShort(0xBE, true)      
    end

    --get temperature from bmp085
    --parameters:
    --num_10x: bool value, if true, return number of 0.1 centi-degree
    --                     default value is false, which return a string , eg: 16.7
    function M.getUT(num_10x)
      write_reg(0x77, 0xF4, 0x2E);
      tmr.delay(10000);
      local temp = getShort(0xF6)
      local X1 = (temp - CO.AC6) * CO.AC5 / 32768
      local X2 = CO.MC * 2048/(X1 + CO.MD)
      local r = (X2 + X1 + 8)/16 
      if(num_10x == true) then 
        return r
      else 
        return ((r/10).."."..(r%10))
      end
    end

    --get raw data of pressure from bmp085
    --parameters:
    --oss: over sampling setting, which is 0,1,2,3. Default value is 0 
    function M.getUP_raw(oss)
      local os = 0
      if ((oss == 0) or (oss == 1) or (oss == 2) or (oss == 3)) and (oss ~= nil) then
        os = oss
      end
      local ov = os * 64
      write_reg(0x77, 0xF4, (0x34 + ov));
      tmr.delay(30000); 
      --delay 30ms, according to bmp085 document, wait time are:
      -- 4.5ms 7.5ms 13.5ms 25.5ms respectively according to oss 0,1,2,3
      local MSB = string.byte(read_reg(0x77, 0xF6))
      local LSB = string.byte(read_reg(0x77, 0xF7))
      local XLSB = string.byte(read_reg(0x77, 0xF8))
      local up_raw = (MSB*65536 + LSB *256 + XLSB)/2^(8 - os)
      return up_raw
    end

    --get calibrated data of pressure from bmp085
    --parameters:
    --oss: over sampling setting, which is 0,1,2,3. Default value is 0
    function M.getUP(oss)
      local os = 0
      if ((oss == 0) or (oss == 1) or (oss == 2) or (oss == 3)) and (oss ~= nil) then
        os = oss
      end
      local raw = M.getUP_raw(os)
      local B5 = M.getUT(true) * 16 - 8;
      local B6 = B5 - 4000
      local X1 = CO.B2 * (B6 * B6 /4096)/2048
      local X2 = CO.AC2 * B6 / 2048
      local X3 = X1 + X2
      local B3 = ((CO.AC1*4 + X3)*2^os + 2)/4
      X1 = CO.AC3 * B6 /8192
      X2 = (CO.B1 * (B6 * B6 / 4096))/65536
      X3 = (X1 + X2 + 2)/4
      local B4 = CO.AC4 * (X3 + 32768) / 32768
      local B7 = (raw -B3) * (50000/2^os)
      local p = B7/B4 * 2
      X1 = (p/256)^2
      X1 = (X1 *3038)/65536
      X2 = (-7357 *p)/65536
      p = p +(X1 + X2 + 3791)/16
      return p
    end

    --get estimated data of altitude from bmp085
    --parameters:
    --oss: over sampling setting, which is 0,1,2,3. Default value is 0
    function M.getAL(oss)
      --Altitudi can be calculated by pressure refer to sea level pressure, which is 101325
      --pressure changes 100pa corresponds to 8.43m at sea level
      return (M.getUP(oss) - 101325)*843/10000
    end

    return M