RocketAltimeter.py

import smbus

import time

# Get I2C bus

bus = smbus.SMBus(1)

# MPL3115A2 address, 0x60(96)

# Select control register, 0x26(38)

# 0xB9(185) Active mode, OSR = 128, Altimeter mode

bus.write_byte_data(0x60, 0x26, 0xB9)

# MPL3115A2 address, 0x60(96)

# Select data configuration register, 0x13(19)

# 0x07(07) Data ready event enabled for altitude, pressure, temperature

bus.write_byte_data(0x60, 0x13, 0x07)

# MPL3115A2 address, 0x60(96)

# Select control register, 0x26(38)

# 0xB9(185) Active mode, OSR = 128, Altimeter mode

bus.write_byte_data(0x60, 0x26, 0xB9)

time.sleep(1)

# MPL3115A2 address, 0x60(96)

# Read data back from 0x00(00), 6 bytes

# status, tHeight MSB1, tHeight MSB, tHeight LSB, temp MSB, temp LSB

data = bus.read_i2c_block_data(0x60, 0x00, 6)

# Convert the data to 20-bits

tHeight = ((data[1] * 65536) + (data[2] * 256) + (data[3] & 0xF0)) / 16

temp = ((data[4] * 256) + (data[5] & 0xF0)) / 16

altitude = tHeight / 16.0

cTemp = temp / 16.0

fTemp = cTemp * 1.8 + 32

# MPL3115A2 address, 0x60(96)

# Select control register, 0x26(38)

# 0x39(57) Active mode, OSR = 128, Barometer mode

bus.write_byte_data(0x60, 0x26, 0x39)

time.sleep(1)

# MPL3115A2 address, 0x60(96)

# Read data back from 0x00(00), 4 bytes

# status, pres MSB1, pres MSB, pres LSB

data = bus.read_i2c_block_data(0x60, 0x00, 4)

# Convert the data to 20-bits

pres = ((data[1] * 65536) + (data[2] * 256) + (data[3] & 0xF0)) / 16

pressure = (pres / 4.0) / 1000.0

# Output data to screen

print "Altitude : %.2f m" %altitude

print "Temperature in Celsius : %.2f C" %cTemp

print "Temperature in Fahrenheit : %.2f F" %fTemp

print "Pressure : %.2f kPa" %pressure