109 lines
2.6 KiB
Lua
109 lines
2.6 KiB
Lua
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------------------------------------------------------------------------------
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-- BMP085 query module
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--
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-- LICENCE: http://opensource.org/licenses/MIT
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-- Vladimir Dronnikov <dronnikov@gmail.com>
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-- Heavily based on work of Christee <Christee@nodemcu.com>
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--
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-- Example:
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-- require("bmp085").read(sda, scl)
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------------------------------------------------------------------------------
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local M
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do
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-- cache
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local i2c, tmr = i2c, tmr
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-- helpers
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local r8 = function(reg)
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i2c.start(0)
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i2c.address(0, 0x77, i2c.TRANSMITTER)
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i2c.write(0, reg)
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i2c.stop(0)
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i2c.start(0)
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i2c.address(0, 0x77, i2c.RECEIVER)
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local r = i2c.read(0, 1)
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i2c.stop(0)
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return r:byte(1)
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end
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local w8 = function(reg, val)
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i2c.start(0)
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i2c.address(0, 0x77, i2c.TRANSMITTER)
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i2c.write(0, reg)
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i2c.write(0, val)
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i2c.stop(0)
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end
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local r16u = function(reg)
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return r8(reg) * 256 + r8(reg + 1)
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end
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local r16 = function(reg)
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local r = r16u(reg)
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if r > 32767 then r = r - 65536 end
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return r
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end
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-- calibration data
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local AC1, AC2, AC3, AC4, AC5, AC6, B1, B2, MB, MC, MD
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-- read
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local read = function(sda, scl, oss)
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i2c.setup(0, sda, scl, i2c.SLOW)
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-- cache calibration data
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if not AC1 then
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AC1 = r16(0xAA)
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AC2 = r16(0xAC)
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AC3 = r16(0xAE)
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AC4 = r16u(0xB0)
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AC5 = r16u(0xB2)
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AC6 = r16u(0xB4)
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B1 = r16(0xB6)
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B2 = r16(0xB8)
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MB = r16(0xBA)
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MC = r16(0xBC)
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MD = r16(0xBE)
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end
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-- get raw P
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local p
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-- NB: optimize for oss = 0
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if not oss then oss = 0 end
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if oss == 0 then
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oss = 0
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w8(0xF4, 0x34)
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tmr.delay(5000)
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p = r8(0xF6) * 256 + r8(0xF7)
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else
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w8(0xF4, 0x34 + 64 * oss)
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tmr.delay(30000)
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p = r8(0xF6) * 65536 + r8(0xF7) * 256 + r8(0xF8)
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p = p / 2^(8 - oss)
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end
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-- get T
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w8(0xF4, 0x2E)
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tmr.delay(5000)
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local t = r16(0xF6)
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local X1 = (t - AC6) * AC5 / 32768
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local X2 = MC * 2048 / (X1 + MD)
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t = (X2 + X1 + 8) / 16
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-- normalize P
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local B5 = t * 16 - 8;
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local B6 = B5 - 4000
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local X1 = B2 * (B6 * B6 / 4096) / 2048
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local X2 = AC2 * B6 / 2048
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local X3 = X1 + X2
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local B3 = ((AC1 * 4 + X3) * 2^oss + 2) / 4
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X1 = AC3 * B6 / 8192
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X2 = (B1 * (B6 * B6 / 4096)) / 65536
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X3 = (X1 + X2 + 2) / 4
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local B4 = AC4 * (X3 + 32768) / 32768
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local B7 = (p - B3) * (50000 / 2^oss)
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p = B7 / B4 * 2
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X1 = (p / 256)^2
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X1 = (X1 * 3038) / 65536
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X2 = (-7357 * p) / 65536
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p = p + (X1 + X2 + 3791) / 16
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-- Celsius * 10, Hg mm * 10
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return t, p * 3 / 40
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end
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-- expose
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M = {
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read = read,
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}
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end
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return M
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