BMP280/BME280 module

Very inefficient way to implement all those calculations

Please use BME280 NodeMCU native library.

Library for BMP280/BME280 Digital Pressure Sensor for ESP8266 lua based firmware NodeMCU integer version.

Due to memory limitations libraries it is better to compile (node.compile()) libraries so it can be use in some more complex scripts.

Compensation formulas follow the double precision floating point algorithm defined in BME280 datasheet (http://ae-bst.resource.bosch.com/media/products/dokumente/bme280/BST-BME280_DS001-11.pdf).

To get air pressure converted to sea level pressure (QNH) you need to specify altitude of the measurement point. Air pressure at given altitude and sea level pressure follow the formula

P = QNH (1 - 2.25577 10^-5 h)^5.25588

where

P = air pressure (Pa)

h = altitude above sea level (m)

QNH = sea level air pressure (m); 101325 for [Standard Atmosphere](https://en.wikipedia.org/wiki/International_Standard_Atmosphere)

Index

• init()
• readAdc()
• compensateT()
• compensateP()
• compensateH()
• altCal()
• qfe2qnh()
• altitude()

Example

d=require("bme280")

alt=320 -- altitude of the measurement place

d:init()

-- calculate coefficient to get air pressure converted to sea level (QNH)
d:altCal(alt)
print("h="..string.format("%9X", d.hH)..string.format("%9X", d.hL).." *2^"..d.hE)

-- read sensor
adc_T = d:readAdc(1)
adc_P = d:readAdc(2)
adc_H = d:readAdc(3)
if not adc_T or not adc_P then return end
print(string.format("adc_T=%X\tadc_P=%X\tadc_H=%X", adc_T, adc_P, adc_H))

-- calculate temperature
T, t_fine = d:compensateT(adc_T)
print((string.gsub(string.format("T=%d.%2d", T/100, T%100), " ", "0")), "t_fine="..t_fine)

-- calculate aire pressure
P = d:compensateP(adc_P, t_fine)
print((string.gsub(string.format("QFE=%d.%3d", P/1000, P%1000), " ", "0")))

-- convert measure air pressure to sea level pressure
QNH = d:qfe2qnh(P, alt)
print((string.gsub(string.format("QNH=%d.%3d", QNH/1000, QNH%1000), " ", "0")))

H = d:compensateH(adc_H, t_fine)
print((string.gsub(string.format("humidity=%d.%3d%%", H/1000, H%1000), " ", "0")))

-- altimeter function - calculate altitude based on current sea level pressure (QNH) and measure pressure
adc_T = d:readAdc(1)
adc_P = d:readAdc(2)
T, t_fine = d:compensateT(adc_T)
P = d:compensateP(adc_P, t_fine)
curAlt=d:altitude(P, QNH)
print(string.gsub(string.format("altitude=%d.%2d", curAlt/100, curAlt%100), " ", "0"), "adc_T="..string.format("%X", adc_T), "adc_P="..string.format("%X", adc_P))

d=nil;package.loaded["bme280"]=nil;

Methods

###init()

####Description Initialize module. Initialization is mandatory before read values.

####Syntax init(sda, scl)

####Parameters

• sda - SDA pin
• scl - SCL pin

####Returns nil

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###readAdc() ####Description Read raw temperature/pressure/relative humidity value.

####Syntax readAdc(meter)

####Parameters

• meter - 1 for temperature, 2 for pressure, 3 for relative humidity

####Returns raw reading value

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###compensateT() ####Description Returns the temperature of the last temperature reading. Calculation follows the algorithm defined in BME280 datasheet.

####Syntax compensateT(adc_T)

####Parameters

• adc_T - raw temperature reading

####Returns

• t - last temperature reading in 0.01ºC (divide by 100 to get ºC).
• t_fine - value to be used in pressure compensation calculation

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###compensateP() ####Description Returns the pressure of the last pressure reading. Calculation follows the algorithm defined in BME280 datasheet.

####Syntax compensateP(adc_P, t_fine)

####Parameters

• adc_P - raw pressure reading
• t_fine - latest t_fine temperature value, returned by compensateT method

####Returns

• P - last pressure reading in Pa (divide by 100 to get commonly used hPa).

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###compensateH() ####Description Returns the pressure of the last pressure reading. Calculation follows the algorithm defined in BME280 datasheet.

####Syntax compensateH(adc_H, t_fine)

####Parameters

• adc_H - raw relative humidity reading
• t_fine - latest t_fine temperature value, returned by compensateT method

####Returns

• H - last relative humidity reading in % times 100(divide by 100 to get %).

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###altCal() Description Calculates and returns coefficient converting current pressure to sea level pressure for given altitude. The result is saved in the library so that for given altitude it does not have to be calculated again.

####Syntax altCal(altitude)

####Parameters

• altitude - altitude in meters of measurement point

####Returns

• cH, cL, cE - (cH << 32 | cL) * 2^cE - double precision floating point coefficient, QNH = P * c

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###qfe2qnh() Description Converts measure pressure to sea level pressure for given altitude. If no altCal(altitude) has been called before or if altitude changes the conversion coefficient is recalculated.

####Syntax qfe2qnh(P, altitude)

####Parameters

• P - measured pressure
• altitude - altitude in meters of measurement point

####Returns

• QNH - sea level pressure

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###altitude() ####Description Calculates altitude for measured pressure and QNH, i.e. altimeter function.

####Syntax altitude(P, QNH)

####Parameters

• P - measured pressure
• QNH - current sea level pressure

####Returns

• altitude - altitude in meters of measurement point

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==== #math64 module Double precision floating point signed numbers arithmetic operations. Used by BMP280 module.

##Index

• fmt()
• shr()
• shl()
• add64()
• mult64()
• div64()
• red()
• ln()
• exp()

###fmt()

####Description Formats number as 64-bit hexadecimal for printing.

####Syntax fmt(H, L)

fmt(H, L, E)

####Parameters

• H - high signed long of 64-bit number
• L - low unsigned long of 64-bit number
• E - (optional) exponent

####Returns

• string with formatted number

####Example

> a=require("math64")
> print("a="..a:fmt(0x12345678, 0x9ABCDEF0))
a=12345678 9ABCDEF0
> print("a="..a:fmt(0x12345678, 0x9ABCDEF0, 20))
a=12345678 9ABCDEF0 *2^20

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###shr()

####Description Bit shift right operation by n bits. It's arithmetic shift (corresponding to bit.arshift). If E is specified the resulting exponent is adjusted accordingly

####Syntax shr(H, L, n)

shr(H, L, n, E)

####Parameters

• H - high signed long of 64-bit number
• L - low unsigned long of 64-bit number
• n - number of bits to shift (1 to 63)
• E - (optional) exponent

####Returns

• H, L, E - right-shifted number

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###shl()

####Description Bit shift left operation by n bits. If E is specified the resulting exponent is adjusted accordingly

####Syntax shl(H, L, n)

shl(H, L, n, E)

####Parameters

• H - high signed long of 64-bit number
• L - low unsigned long of 64-bit number
• n - number of bits to shift (1 to 63)
• E - (optional) exponent

####Returns

• H, L, E - left-shifted number

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###add64()

####Description Signed 64-bit or 96-bit floating point addition.

####Syntax add64(aH, aL, bH, bL)

add64(aH, aL, bH, bL, aE, bE)

####Parameters

• aH - high signed long of 64-bit number a
• aL - low unsigned long of 64-bit number a
• bH - high signed long of 64-bit number b
• bL - low unsigned long of 64-bit number b
• aE - (optional) exponent of a
• bE - (optional) exponent of b

####Returns

• H, L, E - a+b

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###mult64()

####Description Signed 64-bit or 96-bit floating point multiplication. For subtraction do add64(aH, aL, bit.bnot(rH), bit.bnot(rL) + 1).

####Syntax mult64(aH, aL, bH, bL, aE, bE)

####Parameters

• aH - high signed long of 64-bit number a
• aL - low unsigned long of 64-bit number a
• bH - high signed long of 64-bit number b
• bL - low unsigned long of 64-bit number b
• aE - (optional) exponent of a
• bE - (optional) exponent of b

####Returns

• H, L, E - a*b

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###div64() Signed 64-bit or 96-bit floating point division.

####Description

####Syntax div64(aH, aL, bH, bL, aE, bE)

####Parameters

• aH - high signed long of 64-bit number a
• aL - low unsigned long of 64-bit number a
• bH - high signed long of 64-bit number b
• bL - low unsigned long of 64-bit number b
• aE - (optional) exponent of a
• bE - (optional) exponent of b

####Returns

• H, L, E - a/b

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###red()

####Description "Reduce" floating number, i.e. removes 0 from right and adjust exponent accordingly (if floating)

####Syntax red(H, L, E)

####Parameters

• H - high signed long of 64-bit number
• L - low unsigned long of 64-bit number
• E - (optional) exponent

####Returns

• H, L, E - "reduced" number

####Example

> a=require("math64")
> print("a="..a:fmt(a:red(0x12345678, 0x9ABCDEF0, -10)))
a= 1234567 89ABCDEF *2^-6

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###ln()

####Description Approximation of e-based logarithm for (1-x)<2.

The result is -ln(1-x)

####Syntax ln(H, L, E)

####Parameters

• H - high signed long of 64-bit number
• L - low unsigned long of 64-bit number
• E - exponent

####Returns

• H, L, E - -ln(1-x)

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###exp()

####Description Approximation of e-based exponential.

####Example

> a=require("math64")
> H, L, E = 0, 1, -2 -- 0.25
> H, L, E = a:exp(H, L, E)
> print(a:fmt(H, L, E))
2916BB 247B4601 *2^-53 -- 1.28402478337574
> H, L, E = a:add64(0, 1, bit.bnot(H), bit.bnot(L) + 1, 0, E) -- 1-x
> print(a:fmt(H, L, E))
FFF6E944 DB84B9FF *2^-53 -- -0.284024783375799
> H, L, E = a:ln(H, L, E)
> print(a:fmt(H, L, E))
FFFFFBFF FC478323 *2^-44 -- -0.250003548339009

####Syntax exp(kH, kL, kE)

####Parameters

• H - high signed long of 64-bit number
• L - low unsigned long of 64-bit number
• E - exponent

####Returns

• H, L, E - exp(x)

####Example

> a=require("math64")
> H, L, E = 0, 1, 0
> H, L, E = a:exp(H, L, E)
> print(a:fmt(H, L, E))
		0 56FB2A29 *2^-29 -- 2.71815975196659

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