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- ------------------------------------------------------------------------------
- -- BMP085 query module
- --
- -- LICENCE: http://opensource.org/licenses/MIT
- -- Vladimir Dronnikov <dronnikov@gmail.com>
- -- Heavily based on work of Christee <Christee@nodemcu.com>
- --
- -- Example:
- -- dofile("bmp085.lua").read(sda, scl)
- ------------------------------------------------------------------------------
- local M
- do
- -- cache
- local i2c, tmr = i2c, tmr
- -- helpers
- local r8 = function(reg)
- i2c.start(0)
- i2c.address(0, 0x77, i2c.TRANSMITTER)
- i2c.write(0, reg)
- i2c.stop(0)
- i2c.start(0)
- i2c.address(0, 0x77, i2c.RECEIVER)
- local r = i2c.read(0, 1)
- i2c.stop(0)
- return r:byte(1)
- end
- local w8 = function(reg, val)
- i2c.start(0)
- i2c.address(0, 0x77, i2c.TRANSMITTER)
- i2c.write(0, reg)
- i2c.write(0, val)
- i2c.stop(0)
- end
- local r16u = function(reg)
- return r8(reg) * 256 + r8(reg + 1)
- end
- local r16 = function(reg)
- local r = r16u(reg)
- if r > 32767 then r = r - 65536 end
- return r
- end
- -- calibration data
- local AC1, AC2, AC3, AC4, AC5, AC6, B1, B2, MB, MC, MD
- -- read
- local read = function(sda, scl, oss)
- i2c.setup(0, sda, scl, i2c.SLOW)
- -- cache calibration data
- if not AC1 then
- AC1 = r16(0xAA)
- AC2 = r16(0xAC)
- AC3 = r16(0xAE)
- AC4 = r16u(0xB0)
- AC5 = r16u(0xB2)
- AC6 = r16u(0xB4)
- B1 = r16(0xB6)
- B2 = r16(0xB8)
- MB = r16(0xBA)
- MC = r16(0xBC)
- MD = r16(0xBE)
- end
- -- get raw P
- if not oss then oss = 0 end
- if oss <= 0 then oss = 0 end
- if oss > 3 then oss = 3 end
- w8(0xF4, 0x34 + 64 * oss)
- tmr.delay((4 + 3 ^ oss) * 1000)
- local p = r8(0xF6) * 65536 + r8(0xF7) * 256 + r8(0xF8)
- p = p / 2 ^ (8 - oss)
- -- get T
- w8(0xF4, 0x2E)
- tmr.delay(5000)
- local t = r16(0xF6)
- local X1 = (t - AC6) * AC5 / 32768
- local X2 = MC * 2048 / (X1 + MD)
- t = (X2 + X1 + 8) / 16
- -- normalize P
- local B5 = t * 16 - 8;
- local B6 = B5 - 4000
- local X1 = B2 * (B6 * B6 / 4096) / 2048
- local X2 = AC2 * B6 / 2048
- local X3 = X1 + X2
- local B3 = ((AC1 * 4 + X3) * 2 ^ oss + 2) / 4
- X1 = AC3 * B6 / 8192
- X2 = (B1 * (B6 * B6 / 4096)) / 65536
- X3 = (X1 + X2 + 2) / 4
- local B4 = AC4 * (X3 + 32768) / 32768
- local B7 = (p - B3) * (50000 / 2 ^ oss)
- p = B7 / B4 * 2
- X1 = (p / 256) ^ 2
- X1 = (X1 * 3038) / 65536
- X2 = (-7357 * p) / 65536
- p = p + (X1 + X2 + 3791) / 16
- -- Celsius * 10, Hg mm * 10
- return t, p * 3 / 40
- end
- -- expose
- M = {
- read = read,
- }
- end
- return M
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