Raspberry Pi and BMP180 sensor

This bmp180 from Bosch is the best low-cost sensing solution for measuring barometric pressure and temperature. The sensor is soldered onto a PCB with a 3.3V regulator, I2C level shifter and pull-up resistors on the I2C pins. The BMP180 replaces the BMP085.

Specification

• Pressure sensing range: 300-1100 hPa (9000m to -500m above sea level)
• Up to 0.03hPa / 0.25m resolution
• -40 to +85°C operational range, +-2°C temperature accuracy

Here is a breakout which makes it easy to use the sensor, link at the bottom. The sensor will cost about $2.50 so its a nice little, low cost addition to use.

Layout

Here is a layout showing how to connect the sensor to our Raspberry Pi

Code

Save the following as BMP180.py

[codesyntax lang=”python”]

import smbus
import time

bus = smbus.SMBus(1)

# BMP180 address, 0x77
data = bus.read_i2c_block_data(0x77, 0xAA, 22)

# Convert the data
AC1 = data[0] * 256 + data[1]
if AC1 > 32767 :
	AC1 -= 65535
AC2 = data[2] * 256 + data[3]
if AC2 > 32767 :
	AC2 -= 65535
AC3 = data[4] * 256 + data[5]
if AC3 > 32767 :
	AC3 -= 65535
AC4 = data[6] * 256 + data[7]
AC5 = data[8] * 256 + data[9]
AC6 = data[10] * 256 + data[11]
B1 = data[12] * 256 + data[13]
if B1 > 32767 :
	B1 -= 65535
B2 = data[14] * 256 + data[15]
if B2 > 32767 :
	B2 -= 65535
MB = data[16] * 256 + data[17]
if MB > 32767 :
	MB -= 65535
MC = data[18] * 256 + data[19]
if MC > 32767 :
	MC -= 65535
MD = data[20] * 256 + data[21]
if MD > 32767 :
	MD -= 65535

time.sleep(0.5)

bus.write_byte_data(0x77, 0xF4, 0x2E)
time.sleep(0.5)
data = bus.read_i2c_block_data(0x77, 0xF6, 2)

# Convert the data
temp = data[0] * 256 + data[1]

bus.write_byte_data(0x77, 0xF4, 0x74)

time.sleep(0.5)

data = bus.read_i2c_block_data(0x77, 0xF6, 3)

# Convert the data
pres = ((data[0] * 65536) + (data[1] * 256) + data[2]) / 128

# Callibration for Temperature
X1 = (temp - AC6) * AC5 / 32768.0
X2 = (MC * 2048.0) / (X1 + MD)
B5 = X1 + X2
cTemp = ((B5 + 8.0) / 16.0) / 10.0
fTemp = cTemp * 1.8 + 32

# Calibration for Pressure
B6 = B5 - 4000
X1 = (B2 * (B6 * B6 / 4096.0)) / 2048.0
X2 = AC2 * B6 / 2048.0
X3 = X1 + X2
B3 = (((AC1 * 4 + X3) * 2) + 2) / 4.0
X1 = AC3 * B6 / 8192.0
X2 = (B1 * (B6 * B6 / 2048.0)) / 65536.0
X3 = ((X1 + X2) + 2) / 4.0
B4 = AC4 * (X3 + 32768) / 32768.0
B7 = ((pres - B3) * (25000.0))
pressure = 0.0
if B7 < 2147483648L :
	pressure = (B7 * 2) / B4
else :
	pressure = (B7 / B4) * 2
X1 = (pressure / 256.0) * (pressure / 256.0)
X1 = (X1 * 3038.0) / 65536.0
X2 = ((-7357) * pressure) / 65536.0
pressure = (pressure + (X1 + X2 + 3791) / 16.0) / 100

# Calculate Altitude
altitude = 44330 * (1 - ((pressure / 1013.25) ** 0.1903))

# Output data to screen
print "Altitude : %.2f m" %altitude
print "Pressure : %.2f hPa " %pressure
print "Temperature in Celsius : %.2f C" %cTemp
print "Temperature in Fahrenheit : %.2f F" %fTemp

[/codesyntax]

Output

Run the following from the command line by typing in – sudo python BMP180.py

Links

BMP180 Replace BMP085 Digital Barometric Pressure Sensor Board Module For Arduino