MATLAB: How to read temperature and pressure through the bmp180

bmp180

Recently I worked to read the temperature and pressure through a sensor BMP180:
First script
AC1=readRegister(bmp180, hex2dec('AA'));
AC2=readRegister(bmp180, hex2dec('AC'));
AC3=readRegister(bmp180, hex2dec('AE'));
AC4=readRegister(bmp180, hex2dec('B0'));
AC5=readRegister(bmp180, hex2dec('B2'));
AC6=readRegister(bmp180, hex2dec('B4'));
B1=readRegister(bmp180, hex2dec('B6'));
B2=readRegister(bmp180, hex2dec('B8'));
MB=readRegister(bmp180, hex2dec('BA'));
MC=readRegister(bmp180, hex2dec('BC'));
MD=readRegister(bmp180, hex2dec('BE'));
I used the variables as they appear in the sensor datasheet on page 15
Considering only the temperature:
writeRegister(bmp180, hex2dec('F4'), hex2dec('2E'))
pause(0.05)
MSBt=readRegister(bmp180, hex2dec('F6'));
LSBt=readRegister(bmp180, hex2dec('F7'));
UT=double(bitshift(int16(MSBt), 8)) + double(int16(LSBt))
X1=int16(UT)-int16(AC6)*int16(AC5)/2^15;
X2=int16(MC)*2^11/(int16(X1)+int16(MD));
B5=X1+X2;
T=(B5+8)/2^4
However this reading is not correct.
How to read correctly?
AC1 (0xAA, 0xAB) (16 bit) short ??
AC2 (0xAC, 0xAD) (16 bit) short ??
…
write 0x2E into reg 0xF4 ??
read reg 0xF6 (MSB), 0xF7 (LSB) ??
…
write 0x34 + (oss<<6) into reg 0xF4 ….. ??
Note: I am using an Arduino board Mega2560
Thank you in advance

Best Answer

Using your code I was able to figure it out (I think). 1)The cal values are in 8 bit registers so you need to read in the MSB and LSB values of each then concat them to make the actual value 2) you had an error in the calculation of the T (missing ())
Here is the code I am using, hope it helps
clear all
mypi = raspi
mypi.AvailableI2CBuses;
mypi.I2CBusSpeed;
scanI2CBus(mypi,'i2c-1');
BMP180 = i2cdev(mypi,'i2c-1','0x77');
AC1m=int16(readRegister(BMP180, hex2dec('AA'),'int8'));
AC1l=int16(readRegister(BMP180, hex2dec('AB'),'int8'));
AC1 = int32(typecast((bitshift(AC1m,8)+ AC1l),'int16'));
AC2m=int16(readRegister(BMP180, hex2dec('AC'),'int8'));
AC2l=int16(readRegister(BMP180, hex2dec('AD'),'int8'));
AC2 = int32(typecast((bitshift(AC2m,8)+ AC2l),'int16'));
AC3m=int16(readRegister(BMP180, hex2dec('AE'),'int8'));
AC3l=int16(readRegister(BMP180, hex2dec('AF'),'int8'));
AC3 = int32((bitshift(AC3m,8)+ AC3l));
AC4m=int16(readRegister(BMP180, hex2dec('B0'),'int8'));
AC4l=int16(readRegister(BMP180, hex2dec('B1'),'int8'));
AC4 = int32(typecast((bitshift(AC4m,8)+ AC4l),'uint16'));
% AC5=int16(readRegister(BMP180, hex2dec('B2'),'uint16'));
AC5m=int16(readRegister(BMP180, hex2dec('B2'),'int8'));
AC5l=int16(readRegister(BMP180, hex2dec('B3'),'int8'));
AC5 = int32(typecast((bitshift(AC5m,8)+ AC5l),'uint16'));
% AC6=int16(readRegister(BMP180, hex2dec('B4'),'uint16'));
AC6m=int16(readRegister(BMP180, hex2dec('B4'),'int8'));
AC6l=int16(readRegister(BMP180, hex2dec('B5'),'int8'));
AC6 = int32(typecast(bitshift(AC6m,8)+ AC6l,'uint16'));
% B1=int16(readRegister(BMP180, hex2dec('B6'),'int16'));
B1m=int16(readRegister(BMP180, hex2dec('B6'),'int8'));
B1l=int16(readRegister(BMP180, hex2dec('B7'),'int8'));
B1 = int32((bitshift(B1m,8)+ B1l));
% B2=int16(readRegister(BMP180, hex2dec('B8'),'int16'));
B2m=int16(readRegister(BMP180, hex2dec('B8'),'int8'));
B2l=int16(readRegister(BMP180, hex2dec('B9'),'int8'));
B2 = int32((bitshift(B2m,8)+ B2l));
% MB=int16(readRegister(BMP180, hex2dec('BA'),'int16'));
MBm=int16(readRegister(BMP180, hex2dec('Ba'),'int8'));
MBl=int16(readRegister(BMP180, hex2dec('BB'),'int8'));
MB = int32((bitshift(MBm,8)+ MBl));
% MC=int16(readRegister(BMP180, hex2dec('BC'),'int16'));
MCm=int16(readRegister(BMP180, hex2dec('BC'),'int8'));
MCl=int16(readRegister(BMP180, hex2dec('BD'),'int8'));
MC = int32((bitshift(MCm,8)+ MCl));
% MD=int16(readRegister(BMP180, hex2dec('BE'),'int16'));
MDm=int16(readRegister(BMP180, hex2dec('BE'),'int8'));
MDl=int16(readRegister(BMP180, hex2dec('BF'),'int8'));
MD = int32((bitshift(MDm,8)+ MDl));
if readRegister(BMP180, hex2dec('D0'),'int8') ~=hex2dec('55')
    error('Sonething wrong with temperature sensor')
end
writeRegister(BMP180, hex2dec('F4'), hex2dec('2E'),'int8')
pause(4.5E-3)
pause(5*60)
MSBt=int16(readRegister(BMP180, hex2dec('F6'),'int8'));
LSBt=int16(readRegister(BMP180, hex2dec('F7'),'int8'));
UT=int32((bitshift(MSBt, 8)) + (LSBt));
%  UT = int32(27898);
% AC1 = int16(408)
% AC2 = int16(-72)
% AC3 = int16(-14383)
% AC4 = int16(32741)
% AC5 = int16(32757)
% AC6 = int16(23153)
% B1 = int16(6190)
% B2 = int16(4)
% MB = int16(-32768)
% MC = int16(-8711)
% MD = int16(2868)
% 

% 
X1=int32((UT-int32(AC6))*int32(AC5)/(2^15));
X2=int32(int32(MC)*2^11/((X1+int32(MD))));
B5=double(X1+X2);
T=(B5+8)/(2^4)*0.1
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