Tag: featured

For the quadcopter I bought a GY-80 arduino compatible 10 DOF (degrees of freedom) sensor IMU. The small board comes with an accelerometer, a gyroscope, a magnetometer, and a pressure sensor. For now I only need the accelerometer and the gyroscope, and this post deals with connecting the sensor board to the beaglebone back and reading out the results by using the BlackLib library.

First some specifications on the sensor board:

• 3 Axis Gyro
  • ST Microelectronics L3G4200D
  • Address: 0x69
  • Datasheet
• 3 Axis Accelerometer
  • Analog Devices ADXL345
  • Address: 0x53
  • Datasheet
• 3 Axis Magnetometer
  • Honeywell MC5883L
  • Addres: 0x1E
  • Datasheet
• Barometer + Thermometer
  • Bosch BMP085
  • Address: 0x77
  • Datasheet

Connecting the sensors to the beaglebone black is very straightforward. The sensor board supports both 5V and 3.3V power, and in case of the beaglebone al the I2C lines are 3.3V logic levels, I decided to power the sensors with the 3.3V.

To connect the SDA and SCL lines to the beaglebone black board, you need to realise that the beaglebone comes with 3 I2C busses. Only I2C bus 0 and 1 are by default enabled, and used by the system, the third one can be turned on by using the device tree overlays. But I2C bus 0 isn’t exported to the expansion headers so I will have to use I2C bus 1, on expansion header P9, pins 19 and 20, since these are by default enabled, no additional configuration was required.

When powering up the board:

root@beaglebone:~# i2cdetect -y -r 1
0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- 1e --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- 53 UU UU UU UU -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- 69 -- -- -- -- -- --
70: -- -- -- -- -- -- -- 77

With the BlackLib library, reading out the sensor data was fairly easy. Sources can be found on my github.

With this final hardware installed on the quadcopter, the assembly has been completed!

[UPDATE]: this was on kernel version 3.8.  I’ve started over on kernel version 4.4, and since the PWM code in BlackLib (v2 and v3) aren’t working with 4.4, I’ve decided to do the implementation myself.  All the C++11 options, dialects, etc can be removed from the eclipse project settings.
BlackLib v3 does have a nice Makefile now, so building and using it doesn’t require you to set up a seperate project in eclipse anymore, you just need to specify the include path and the library path.

First you’ll need the cross compiler. For example, on Ubuntu:
sudo apt-get install gcc-arm-linux-gnueabihf

This will give you:
nicky@nicky-Precision-M4800:~/Projects/BlackLib$ arm-linux-gnueabihf-g++ --version
arm-linux-gnueabihf-g++ (Ubuntu/Linaro 4.9.1-16ubuntu6) 4.9.1
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

nicky@nicky-Precision-M4800:~/Projects/BlackLib$ arm-linux-gnueabihf-gcc –version
arm-linux-gnueabihf-gcc (Ubuntu/Linaro 4.9.1-16ubuntu6) 4.9.1
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

However it seems that this version is a bit more recent then the one BlackLib has been developed with, and it won’t compile due to a few missing includes. You can find this fix on my github repo: https://github.com/panic1/BlackLib/tree/unistd

Now I will be using eclipse to build a shared library from this BlackLib code, in my setup I’m using Eclipse Luna with CDT.

1. Create a new C++ Project, Click next.
2. Project name: BlackLib
3. Uncheck default location, and select the location where you checked out the BlackLib code
4. Select Shared Library, Empty Project
5. Select cross toolchain (you might need to uncheck the checkmark at the bottom to show all toolchain options), and click next
6. The toolchain prefix: arm-linux-gnueabihf-. Click finish

Now the fun starts, BlackLib is written with quite advanced C++11 functionality, and the compiler will have to be enable to allow these experimental features:

1. Right click on the project, select Properties
2. Go to C/C++ Build, Settings
3. In the Cross Settings the prefix should be set to arm-linux-gnueabihf- (just in case you’ve forgotten in a previous step
4. In the Cross C++ Compiler, Dialect, Language standard should be set to ISO C++11
5. In the Cross C++ Compiler, Preprocessor, add a new symbol __GXX_EXPERIMENTAL_CXX0X__
6. In the Cross C++ Compiler, Miscellaneous, check the Position Independent Code (-fPIC)
7. Apply

As we don’t need them in the resulting library, in the project you can right click, go to Resource Configuration, and Exclude from Build the following folders:

• SPI_SETUP
• V1_0
• V2_0/SPI_SETUP
• V2_0/exampleAndTiming
• exampleAndTiming.cpp

Now go ahead and build the project, this should result in a libBlackLib.so file we’ll start to use in the next steps.

Using the library in a new project is pretty straight forward:

Create a new C++ project in Eclipse, choose Empty Project and the Cross GCC toolchain, and click next. The toolchain prefix should be arm-linux-gnueabihf-, just like before.

Right click the project, and go to Properties, Project References and select the BlackLib project to be referenced.
Go to C/C++ Build, Settings, and add the path to the BlackLib/v2.0 folder Cross G++ Compiler Includes, and Cross G++ Linker Libraries should include the BlackLib library, and the path to the BlackLib/Debug where the libBlackLib.so file can be found.

To run your application on the Beaglebone board, you will first have to copy the libBlackLib.so file. There are several valid locations where Linux searches for shared libraries, I usually put it in /usr/lib/. Then copy your application binary, location doesn’t really matter, for example /root or /home/debian, make the binary executable (chmod), and run it.