Beaglebone and MS5611 barometric pressure sensor example in python

In this article we look at another sensor – this time its the MS5611 and we will connect it to our Beaglebone and we will have a python example

First lets take a look at the sensor in question

This barometric pressure sensor is optimized for altimeters and variometers with an altitude resolution of 10 cm. The sensor module includes a high linearity pressure sensor and an ultra-low power 24 bit ΔΣ ADC with internal factory calibrated coefficients.

It provides a precise digital 24 Bit pressure and temperature value and different operation modes that allow the user to optimize for conversion speed and current consumption.

A high resolution temperature output allows the implementation of an altimeter/thermometer function without any additional sensor.

The MS5611-01BA can be interfaced to virtually any microcontroller. The communication protocol is simple, without the need of programming internal registers in the device.

Small dimensions of only 5.0 mm x 3.0 mm and a height of only 1.0 mm allow for integration in mobile devices. This new sensor module generation is based on leading MEMS technology and latest benefits from MEAS Switzerland proven experience and know-how in high volume manufacturing of altimeter modules, which have been widely used for over a decade. The sensing principle employed leads to very low hysteresis and high stability of both pressure and temperature signal.

Features

• High resolution module, 10 cm
• Fast conversion down to 1 ms
• Low power, 1 µA (standby < 0.15 µA)
• QFN package 5.0 x 3.0 x 1.0 mm³
• Supply voltage 1.8 to 3.6 V
• Integrated digital pressure sensor (24 bit ΔΣ ADC)
• Operating range: 10 to 1200 mbar, -40 to +85 °C
• I²C and SPI interface up to 20 MHz
• No external components (Internal oscillator)
• Excellent long term stability

Parts Required

Schematic/Connection

Code Example

Save this as MS5611.py. My sensor used I2c address 0x77, you may have to change this to 0x76 if you have a different one

[codesyntax lang=”python”]

# Distributed with a free-will license.
# Use it any way you want, profit or free, provided it fits in the licenses of its associated works.
# MS5611_01BXXX
# This code is designed to work with the MS5611_01BXXX_I2CS I2C Mini Module available from ControlEverything.com.
# https://www.controleverything.com/content/Analog-Digital-Converters?sku=MS5611-01BXXX_I2CS_A01#tabs-0-product_tabset-2

import smbus
import time

# Get I2C bus
bus = smbus.SMBus(2)

# MS5611_01BXXX address, 0x77(118)
#		0x1E(30)	Reset command
bus.write_byte(0x77, 0x1E)

time.sleep(0.5)

# Read 12 bytes of calibration data
# Read pressure sensitivity
data = bus.read_i2c_block_data(0x77, 0xA2, 2)
C1 = data[0] * 256 + data[1]

# Read pressure offset
data = bus.read_i2c_block_data(0x77, 0xA4, 2)
C2 = data[0] * 256 + data[1]

# Read temperature coefficient of pressure sensitivity
data = bus.read_i2c_block_data(0x77, 0xA6, 2)
C3 = data[0] * 256 + data[1]

# Read temperature coefficient of pressure offset
data = bus.read_i2c_block_data(0x77, 0xA8, 2)
C4 = data[0] * 256 + data[1]

# Read reference temperature
data = bus.read_i2c_block_data(0x77, 0xAA, 2)
C5 = data[0] * 256 + data[1]

# Read temperature coefficient of the temperature
data = bus.read_i2c_block_data(0x77, 0xAC, 2)
C6 = data[0] * 256 + data[1]

# MS5611_01BXXX address, 0x76(118)
#		0x40(64)	Pressure conversion(OSR = 256) command
bus.write_byte(0x77, 0x40)

time.sleep(0.5)

# Read digital pressure value
# Read data back from 0x00(0), 3 bytes
# D1 MSB2, D1 MSB1, D1 LSB
value = bus.read_i2c_block_data(0x77, 0x00, 3)
D1 = value[0] * 65536 + value[1] * 256 + value[2]

# MS5611_01BXXX address, 0x76(118)
#		0x50(64)	Temperature conversion(OSR = 256) command
bus.write_byte(0x77, 0x50)

time.sleep(0.5)

# Read digital temperature value
# Read data back from 0x00(0), 3 bytes
# D2 MSB2, D2 MSB1, D2 LSB
value = bus.read_i2c_block_data(0x77, 0x00, 3)
D2 = value[0] * 65536 + value[1] * 256 + value[2]

dT = D2 - C5 * 256
TEMP = 2000 + dT * C6 / 8388608
OFF = C2 * 65536 + (C4 * dT) / 128
SENS = C1 * 32768 + (C3 * dT ) / 256
T2 = 0
OFF2 = 0
SENS2 = 0

if TEMP >= 2000 :
	T2 = 0
	OFF2 = 0
	SENS2 = 0
elif TEMP < 2000 :
	T2 = (dT * dT) / 2147483648
	OFF2 = 5 * ((TEMP - 2000) * (TEMP - 2000)) / 2
	SENS2 = 5 * ((TEMP - 2000) * (TEMP - 2000)) / 4
	if TEMP < -1500 :
		OFF2 = OFF2 + 7 * ((TEMP + 1500) * (TEMP + 1500))
		SENS2 = SENS2 + 11 * ((TEMP + 1500) * (TEMP + 1500)) / 2

TEMP = TEMP - T2
OFF = OFF - OFF2
SENS = SENS - SENS2
pressure = ((((D1 * SENS) / 2097152) - OFF) / 32768.0) / 100.0
cTemp = TEMP / 100.0
fTemp = cTemp * 1.8 + 32

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

[/codesyntax]

Output

Run this example and you should see the following.

debian@beaglebone:/var/lib/cloud9/$ python MS5611.py
Pressure : 992.17 mbar
Temperature in Celsius : 21.62 C
Temperature in Fahrenheit : 70.92 F
debian@beaglebone:/var/lib/cloud9/$ python MS5611.py
Pressure : 992.12 mbar
Temperature in Celsius : 21.55 C
Temperature in Fahrenheit : 70.79 F

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