Beaglebone Black

Introduce OpenPythonSensor Library

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Introduce the Python driven, I2C focused, Embedded Linux application level library for digital sensors – OpenPythonLibrary.

The very first version includes supports for:

  • BMP180 Barometric Pressure sensor;
  • HTU21D Relative Humidity sensor (Only support Beaglebone Black at this moment);
  • SI1145 Proximity/UV/Ambient Light sensor;
  • TMP007 Infrared Thermopile sensor;
  • HMC6352 Digital Compass;
  • MPU6050 Six-Axis (Gyro + Accelerometer) MEMS;

The I2C bus is set to 1 in OpenPythonSensor / ops_base / ops_i2cbase.py and can be modified to support more development platforms. The python-smbus is a prerequisite of this library.

The library can be found at Github under MIT License.

Example usage of the library
#!/usr/bin/python
from lib_htu21d import HTU21D
 
# Initialize the library
htu = HTU21D()
 
temp = htu.readTemperatureData()
rh = htu.readHumidityData()
 
print "Temperature: %.2f C, Humidity: %.2f %%" % (temp, rh)
Clone the code
git clone https://github.com/randymxj/OpenPythonSensor.git
Download the library

Click -> GitHub_Logo to download

Part of the library is ported from Adafruit-Raspberry-Pi-Python-Code and should remain it’s original license. Some driver is referenced from both Adafruit and Sparkfun and thanks to their original work.

More sensor support will coming soon!

 

python powered Boris_Tux_PNG

How about build a weather station with Beaglebone Black and Node.JS?

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I’m able to get some sensor data with Beaglebone Black by the help of Adafruit-Raspberry-Pi-Python-Code on my HMC6352 and HTU21D driver, but what’s next?

Sep 2014: Merging the application with the new OpenPythonSensor driver library, and deploy all the software (MongoDB, Sensor data gather and save with Python, Backend/Frontend application with Node.JS) on a single Beaglebone Black board.

 

By pushing the sensor data (Temperature, Humidity, Pressure, UVIndex) into a database, an internet front-end application is able to pull and display the data to the users.

Screenshot with plot

 

Embedded solution: A Beaglebone Black (Ubuntu) with HTU21D (Temperature / Humidity), BMP180(Temperature / Pressure) and SI1145 (Proximity/UV/Ambient Light) sensor. A Python script driven software measures the environment data and push data set to database (MongoDB).

Internet based front-end / back-end solution: Node.JS with Express and Mongoose. Back-end Node.JS code to query the database and send to front-end Angular JS function by AJAX. Supported by jQuery, Bootstrap and Chart.JS.

Screenshot with data

 

Demo is available at here. Code is shared under MIT License and can be accessed here on Github.

Beaglebone Black with Sensors

Python Library for HTU21D Humidity Sensor on Beaglebone Black and Raspberry Pi with Adafruit_I2C

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Here is a python library for the HTU21D Humidity Sensor Module with data output of temperature and relative humidity. Code works well with Beaglebone Black and should also works with Raspberry Pi.

Looks like there is some I2C address issue with this driver on the Pi. Please use with caution. I only did some test for this code on a Beaglebone Black with a Sparkfun HTU21D sensor module.

The HTU21D has an I2C address of 0x40, but it won’t respond to the i2cdetect command on Beaglebone Black stock image.

Also note this module will not accept any unexpected i2c data write/read.

Library and example code can be checked out at Github.

#!/usr/bin/python
 
import time
from Adafruit_I2C import Adafruit_I2C
 
# ===========================================================================
# HTU21D Class
# ===========================================================================
 
class HTU21D:
	i2c = None
 
	# HTU21D Address
	address = 0x40
 
	# Commands
	TRIGGER_TEMP_MEASURE_HOLD = 0xE3
	TRIGGER_HUMD_MEASURE_HOLD = 0xE5
	READ_USER_REG = 0xE7
 
	# Constructor
	def __init__(self):
		self.i2c = Adafruit_I2C(self.address)
 
	def readUserRegister(self):
		# Read a byte
		value = self.i2c.readU8(self.READ_USER_REG)
 
		return value
 
	def readTemperatureData(self):
		# value[0], value[1]: Raw temperature data
		# value[2]: CRC
		value = self.i2c.readList(self.TRIGGER_TEMP_MEASURE_HOLD, 3)
 
		if not self.crc8check(value):
			return -255
 
		rawTempData = ( value[0] << 8 ) + value[1]
 
		# Zero out the status bits but keep them in place
		rawTempData = rawTempData & 0xFFFC;
 
		# Calculate the actual temperature
		actualTemp = -46.85 + (175.72 * rawTempData / 65536)
 
		return actualTemp
 
	def readHumidityData(self):
		# value[0], value[1]: Raw relative humidity data
		# value[2]: CRC
		value = self.i2c.readList(self.TRIGGER_HUMD_MEASURE_HOLD, 3)
 
		if not self.crc8check(value):
			return -255
 
		rawRHData = ( value[0] << 8 ) + value[1]
 
		# Zero out the status bits but keep them in place
		rawRHData = rawRHData & 0xFFFC;
 
		# Calculate the actual RH
		actualRH = -6 + (125.0 * rawRHData / 65536)
 
		return actualRH
 
	def crc8check(self, value):
		remainder = ( ( value[0] << 8 ) + value[1] ) << 8
		remainder |= value[2]
 
		# POLYNOMIAL = 0x0131 = x^8 + x^5 + x^4 + 1
		# divsor = 0x988000 is the 0x0131 polynomial shifted to farthest left of three bytes
		divsor = 0x988000
 
		for i in range(0, 16):
			if( remainder & 1 << (23 - i) ): 				remainder ^= divsor 			divsor = divsor >> 1
 
		if remainder == 0:
			return True
		else:
			return False

Change i2c bus frequency on Beaglebone Black

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Normally one can inspect the i2c bus frequency by

dmesg |grep i2c

According and thanks to the discussion at here

The i2c bus frequency can be changed by edit the Linux device tree dtb file:

1. backup the original .dtb

cp /boot/am335x-boneblack.dtb /boot/am335x-boneblack.dtb.orig

2. generate the dts from the dtb

dtc -I dtb -O dts -o am335x-boneblack.dts /boot/am335x-boneblack.dtb

3. modify the dts with a text editor

i2c@4819c000 {
compatible = "ti,omap4-i2c";
#address-cells = <0x1>;
#size-cells = <0x0>;
ti,hwmods = "i2c3";
reg = <0x4819c000 0x1000>;
interrupts = <0x1e>;
status = "okay";
pinctrl-names = "default";
pinctrl-0 = <0x7>;
clock-frequency = <0x186a0>;
linux,phandle = <0x27>;
phandle = <0x27>;

4. generate the dtb from the modified dts

dtc -I dts -O dtb -o am335x-boneblack.dtb am335x-boneblack.dts

Where the i2c@4819c000 is the i2c address:

  • i2c0: 0x44E0B000 (Not available on header)
  • i2c1: 0x4802A000 (Not enabled by default)
  • i2c2: 0x4819C000 (The actual one for configured i2c-1 in Linux, although the register name/expansion port is i2c2)

And the clock-frequency = <0x186a0> is the frequency, 0x186a0 = 100000 = 100KHz here is the default i2c-1 (Expansion port i2c2) frequency for stock beaglebone black image.

5. and finally copy the dtb back to /boot/

cp am335x-boneblack.dtb /boot/am335x-boneblack.dtb

Boris_Tux_PNG

Read heading output from compass IC HMC6352 on Beaglebone Black / Raspberry Pi with Adafruit_I2C

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Note: Although the datasheet has an I2C address 0x42 on file, the recognized address for this HMC6352 is actually 0x42>>1 which is 0x21.

Also looks like this IC doesn’t care about the register address at all, so put 0x0 in the register address field would be fine.

Code/Driver tested with Beaglebone Black and Sparkfun HMC6352 Module.

The HMC6352 library can be checked out at Github.

#!/usr/bin/python
 
import time
from Adafruit_I2C import Adafruit_I2C
 
# ===========================================================================
# HMC6352 Class
# ===========================================================================
 
class HMC6352 :
	i2c = None
 
	# HMC6352 Address
	address = 0x42 >> 1
 
	# Commands
	CMD_READ_DATA = 0x41
	CMD_ENTER_USER_CALIBRATION = 0x45
	CMD_EXIT_USER_CALIBRATION = 0x4C
 
	# Constructor
	def __init__(self):
		self.i2c = Adafruit_I2C(self.address)
 
	def userCalibration(self):
		"Write 0x45 for calibration and write 0x4C for leave after 20s"
		self.i2c.write8(0x0, self.CMD_ENTER_USER_CALIBRATION)
		time.sleep(20)
		self.i2c.write8(0x0, self.CMD_EXIT_USER_CALIBRATION)
 
	def readData(self):
		"Read the heading data by write a 0x41 first"
		self.i2c.write8(0x0, self.CMD_READ_DATA)
		# Wait 6 ms
		time.sleep(0.006)
		# Read 2 bytes
		value = self.i2c.readU16(0x0)
		# Reverse the data byte order
		value = self.i2c.reverseByteOrder(value)
		# Convert to 360.0 range from the raw integer value
		value = float('%0.1f'%value)/10
 
		return value