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barometric-i2c-capture
executable file
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barometric-i2c-capture
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#!/usr/bin/python
import smbus
import time
bus = smbus.SMBus(1)
b1 = bus.read_i2c_block_data(0x76, 0x88, 24)
# Convert the data
# Temp coefficents
dig_T1 = b1[1] * 256 + b1[0]
dig_T2 = b1[3] * 256 + b1[2]
if dig_T2 > 32767 :
dig_T2 -= 65536
dig_T3 = b1[5] * 256 + b1[4]
if dig_T3 > 32767 :
dig_T3 -= 65536
# Pressure coefficents
dig_P1 = b1[7] * 256 + b1[6]
dig_P2 = b1[9] * 256 + b1[8]
if dig_P2 > 32767 :
dig_P2 -= 65536
dig_P3 = b1[11] * 256 + b1[10]
if dig_P3 > 32767 :
dig_P3 -= 65536
dig_P4 = b1[13] * 256 + b1[12]
if dig_P4 > 32767 :
dig_P4 -= 65536
dig_P5 = b1[15] * 256 + b1[14]
if dig_P5 > 32767 :
dig_P5 -= 65536
dig_P6 = b1[17] * 256 + b1[16]
if dig_P6 > 32767 :
dig_P6 -= 65536
dig_P7 = b1[19] * 256 + b1[18]
if dig_P7 > 32767 :
dig_P7 -= 65536
dig_P8 = b1[21] * 256 + b1[20]
if dig_P8 > 32767 :
dig_P8 -= 65536
dig_P9 = b1[23] * 256 + b1[22]
if dig_P9 > 32767 :
dig_P9 -= 65536
# BMP280 address, 0x76(118)
# Select Control measurement register, 0xF4(244)
# 0x27(39) Pressure and Temperature Oversampling rate = 1
# Normal mode
bus.write_byte_data(0x76, 0xF4, 0x27)
# BMP280 address, 0x76(118)
# Select Configuration register, 0xF5(245)
# 0xA0(00) Stand_by time = 1000 ms
bus.write_byte_data(0x76, 0xF5, 0xA0)
time.sleep(0.5)
# BMP280 address, 0x76(118)
# Read data back from 0xF7(247), 8 bytes
# Pressure MSB, Pressure LSB, Pressure xLSB, Temperature MSB, Temperature LSB
# Temperature xLSB, Humidity MSB, Humidity LSB
data = bus.read_i2c_block_data(0x76, 0xF7, 8)
# Convert pressure and temperature data to 19-bits
adc_p = ((data[0] * 65536) + (data[1] * 256) + (data[2] & 0xF0)) / 16
adc_t = ((data[3] * 65536) + (data[4] * 256) + (data[5] & 0xF0)) / 16
# Temperature offset calculations
var1 = ((adc_t) / 16384.0 - (dig_T1) / 1024.0) * (dig_T2)
var2 = (((adc_t) / 131072.0 - (dig_T1) / 8192.0) * ((adc_t)/131072.0 - (dig_T1)/8192.0)) * (dig_T3)
t_fine = (var1 + var2)
cTemp = (var1 + var2) / 5120.0
fTemp = cTemp * 1.8 + 32
# Pressure offset calculations
var1 = (t_fine / 2.0) - 64000.0
var2 = var1 * var1 * (dig_P6) / 32768.0
var2 = var2 + var1 * (dig_P5) * 2.0
var2 = (var2 / 4.0) + ((dig_P4) * 65536.0)
var1 = ((dig_P3) * var1 * var1 / 524288.0 + ( dig_P2) * var1) / 524288.0
var1 = (1.0 + var1 / 32768.0) * (dig_P1)
p = 1048576.0 - adc_p
p = (p - (var2 / 4096.0)) * 6250.0 / var1
var1 = (dig_P9) * p * p / 2147483648.0
var2 = p * (dig_P8) / 32768.0
pressure = (p + (var1 + var2 + (dig_P7)) / 16.0) / 100
fh = open('/home/pi/ramdisk/barometricdata', 'w')
fh.write("%.2f,%.2f" % (cTemp, pressure))
fh.close()
# Output data to screen
#print "Temperature in Celsius : %.2f C" %cTemp
#print "Temperature in Fahrenheit : %.2f F" %fTemp
#print "Pressure : %.2f hPa " %pressure