' reading the BMP085 pressure sensor
' TassyJim 06 JAN 2014
Cls
print
Dim BMPData(2) ' store data from BMP085
dim cal(11) ' calibration data
oss = 0 ' over sampling 0 to 3
alt = 240 ' your altitude in metres
f$="%6.1f" ' format string
BMP085calMEM = &HAA ' start of 11 calibration values
BMP085address = &H77 ' BMP085 address
BMP085control = &HF4 ' BMP085 control register
BMP085temp = &H2E ' BMP085 temperature command
BMP085pres = &H34 ' BMP085 pressure command
BMP085pres = BMP085pres + oss*&H40 ' adjust command for oversampling
BMP085reading = &HF6 ' register for results of reading

I2CEN 400, 200 ' Enable I2C. use slow speeds for long leads
pause 20

z = Calibrate() ' read the calibration data

do
t=temperature()
p=pressure(oss)
p0=Psl(p,alt)
print time$,"T:",format$( t,f$);" P:",format$(p/100,f$);" P(sl):",format$(p0/100,f$)
pause (300000) ' delay 5 minutes between readings
loop until k$ = "q" or k$ = "Q"

end

function Calibrate()
' needs to be called once for each module.
' safest to do it on every program start.
local n, calMEM
calMEM= BMP085calMEM
for n = 1 to 11
I2CSEND BMP085address, 0, 1, calMEM ' first calibration location
pause 1
I2CRCV BMP085address, 0, 2, BMPData(0)
'print BMPData(1), BMPData(0)*256 + BMPData(1)
cal(n) = BMPData(0)*256 + BMPData(1)
if n < 4 or n > 6 then ' need to convert some to signed numbers
if cal(n) > 32767 then
cal(n) = cal(n) - 65536
endif
endif
'print n,cal(n)
pause 1
calMEM=calMEM+2 ' advance to the next calibration location
next n
end function

function temperature()
' returns the temperature in degrees C to one decimal place
local UT, x1, x2, b5
I2CSEND BMP085address, 0, 2, BMP085control, BMP085temp
pause 5
I2CSEND BMP085address, 0, 1, BMP085reading
I2CRCV BMP085address, 0, 2, BMPData(0)
UT = BMPData(0)*256 + BMPData(1)
'calculate true temperature
x1= int( (UT-cal(6))*cal(5)/32768)
x2=int( cal(10)*2048/(x1+cal(11)))
b5=x1+x2
temperature = int((b5+8)/16)/10
end function

function pressure(oss)
' returns the pressure in pascals. Divide by 100 for millibars
' recalculates the temperatre.
' time could be saved by reading the temperature once evry 10 minutes
' when taking readings at short intervals
local UT, UP, x1, x2, x3, b5, b6, b7, pres, p
pres = BMP085pres + oss*&H40
I2CSEND BMP085address, 0, 2, BMP085control, BMP085temp
pause 5
I2CSEND BMP085address, 0, 1, BMP085reading
I2CRCV BMP085address, 0, 2, BMPData(0)
UT = BMPData(0)*256 + BMPData(1)
I2CSEND BMP085address, 0, 2, BMP085control, pres
if oss = 0 then ' different oversampling requires different
pause 5 ' reading times
elseif oss = 1 then
pause 8
elseif oss = 2 then
pause 14
else
pause 26
endif
I2CSEND BMP085address, 0, 1, BMP085reading
I2CRCV BMP085address, 0, 2, BMPData(0)
UP = BMPData(0)*256 + BMPData(1)
I2CSEND BMP085address, 0, 1, BMP085reading+2
I2CRCV BMP085address, 0, 1, BMPData(0)
UP=(UP*256+BMPData(0))/2^(8-oss)
'calculate true temperature
x1= int( (UT-cal(6))*cal(5)/32768)
x2=int( cal(10)*2048/(x1+cal(11)))
b5=x1+x2
t=int((b5+8)/16)/10
'print "Temperature: ",t
'calculate true atmospheric pressure
b6 = b5 - 4000
x1 = int((cal(8)*(b6*b6/4096))/2048)
x2 = int(cal(2)*b6/2048)
x3 = x1 + x2
b3 = int(((cal(1)*4+x3)*2^oss +2)/4)
x1 = int(cal(3)*b6/8192)
x2 = int((cal(7)*(b6*b6/4096))/65536)
x3 = int(((x1+x2)+2)/4)
b4 = int(cal(4)*x3/32768+cal(4))
b7 = int((UP - b3)*(50000/2^oss))
p = int((b7*2)/b4)
x1 = int(int(p/256)*int(p/256))
x1 = int((x1*3038)/65536)
x2 = int((-7357*p)/65536)
pressure = int(p+(x1 + x2 + 3791)/16)
end function

function Psl(p, alt)
'given local pressure and altitude, returns pressure at sea level
Psl= p/(1-alt/44330)^5.255
end function