Category Archives: Robotics

Duinotech Hall Effect Sensor with RaspberryPi

Hi everyone,

This is just a quick post to cover how the Duinotech hall effect sensor module (XC-4434) can be hooked up to a RaspberryPi.

Sample Code

The code below will output a zero when the sensor is activated by a magnet, otherwise a zero.


import time
import datetime
import RPi.GPIO as GPIO

# Define constants
BUCKET_HALL_EFFECT_SIG_PIN = 14

# Setup GPIO pins
GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)
GPIO.setup(BUCKET_HALL_EFFECT_SIG_PIN, GPIO.IN, pull_up_down=GPIO.PUD_UP) # Important

while True:
print(str(GPIO.input(BUCKET_HALL_EFFECT_SIG_PIN))
time.sleep(0.5)

Wiring

Example

When near a magnetic field the light on the sensor will turn on. If you’re using the sample code above, a zero will be shown when close to a magnet, otherwise a 1.

Misc

Purchased from: https://www.jaycar.com.au/arduino-compatible-hall-effect-sensor-module/p/XC4434

Spec Sheet: Z7275

Could not find a version that satisfied the requirement smbus/python3-smbus

Hi everyone,

I ran into a bit of an issue installing smbus on Python3.5. It looks like all you have to do is use smbus2:

pip3.5 install smbus2

Collecting smbus2
Downloading smbus2-0.2.0.tar.gz
Building wheels for collected packages: smbus2
Running setup.py bdist_wheel for smbus2 … done
Stored in directory: /root/.cache/pip/wheels/90/71/b4/9f90d8e2d0349ab55fef07169a81bd8f925965f16174e2f809
Successfully built smbus2
Installing collected packages: smbus2
Successfully installed smbus2-0.2.0

Thanks to the following link: https://www.raspberrypi.org/forums/viewtopic.php?t=192909

Pillow Install Fails – Python 3.5.2

Hi everyone,

Pillow install fails

I ran into a bit of an issue trying to install Pillow on Raspbian with Python 3.5.2. The full error is below, but the solution was simply to install the following:

sudo apt-get install libjpeg8-dev
sudo pip3.5 install pillow

sudo pip3.5 install pillow
Collecting pillow
Using cached Pillow-4.3.0.tar.gz
Requirement already satisfied: olefile in /usr/local/lib/python3.5/site-packages (from pillow)
Installing collected packages: pillow
Running setup.py install for pillow … error
Complete output from command /usr/local/bin/python3.5 -u -c “import setuptools, tokenize;__file__=’/tmp/pip-build-inj0l_9q/pillow/setup.py’;f=getattr(tokenize, ‘open’, open)(__file__);code=f.read().replace(‘\r\n’, ‘\n’);f.close();exec(compile(code, __file__, ‘exec’))” install –record /tmp/pip-xp_x4w_5-record/install-record.txt –single-version-externally-managed –compile:
running install
running build
running build_py
creating build
creating build/lib.linux-armv7l-3.5
creating build/lib.linux-armv7l-3.5/PIL
copying PIL/MicImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageMath.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/WebPImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImagePath.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageGrab.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/SunImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/__init__.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageEnhance.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageMorph.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/XpmImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/EpsImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/FtexImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/WmfImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/FitsStubImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageDraw2.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/IptcImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/_binary.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/MpoImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/Hdf5StubImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/Image.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/MspImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageWin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/GimpPaletteFile.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageTk.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PSDraw.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/McIdasImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/SgiImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageStat.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageChops.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PdfImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/features.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PcfFontFile.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PcxImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageOps.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImagePalette.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/TgaImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageSequence.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/_util.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/TiffTags.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/BmpImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/DdsImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ExifTags.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PyAccess.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PpmImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageCms.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PaletteFile.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/XVThumbImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/IcoImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageFilter.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageFont.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/GifImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/GbrImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/XbmImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PngImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/FontFile.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/IcnsImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/TiffImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/_tkinter_finder.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/DcxImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/OleFileIO.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/SpiderImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/JpegImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/GribStubImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/MpegImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PalmImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/BdfFontFile.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/GimpGradientFile.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PsdImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/WalImageFile.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageFile.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PcdImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/version.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/FpxImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageQt.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/Jpeg2KImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageDraw.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/GdImageFile.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ContainerIO.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/CurImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/FliImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageMode.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/JpegPresets.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PixarImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageColor.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/BufrStubImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageTransform.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageShow.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/TarIO.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImtImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
running egg_info
writing dependency_links to Pillow.egg-info/dependency_links.txt
writing requirements to Pillow.egg-info/requires.txt
writing top-level names to Pillow.egg-info/top_level.txt
writing Pillow.egg-info/PKG-INFO
warning: manifest_maker: standard file ‘-c’ not found

reading manifest file ‘Pillow.egg-info/SOURCES.txt’
reading manifest template ‘MANIFEST.in’
warning: no files found matching ‘*.sh’
no previously-included directories found matching ‘docs/_static’
warning: no previously-included files found matching ‘.coveragerc’
warning: no previously-included files found matching ‘codecov.yml’
warning: no previously-included files found matching ‘.editorconfig’
warning: no previously-included files found matching ‘.landscape.yaml’
warning: no previously-included files found matching ‘.travis’
warning: no previously-included files found matching ‘.travis/*’
warning: no previously-included files found matching ‘appveyor.yml’
warning: no previously-included files found matching ‘build_children.sh’
warning: no previously-included files found matching ‘tox.ini’
warning: no previously-included files matching ‘.git*’ found anywhere in distribution
warning: no previously-included files matching ‘*.pyc’ found anywhere in distribution
warning: no previously-included files matching ‘*.so’ found anywhere in distribution
writing manifest file ‘Pillow.egg-info/SOURCES.txt’
running build_ext

The headers or library files could not be found for jpeg,
a required dependency when compiling Pillow from source.

Please see the install instructions at:
https://pillow.readthedocs.io/en/latest/installation.html

Traceback (most recent call last):
File “/tmp/pip-build-inj0l_9q/pillow/setup.py”, line 787, in
zip_safe=not (debug_build() or PLATFORM_MINGW), )
File “/usr/local/lib/python3.5/distutils/core.py”, line 148, in setup
dist.run_commands()
File “/usr/local/lib/python3.5/distutils/dist.py”, line 955, in run_commands
self.run_command(cmd)
File “/usr/local/lib/python3.5/distutils/dist.py”, line 974, in run_command
cmd_obj.run()
File “/usr/local/lib/python3.5/site-packages/setuptools/command/install.py”, line 61, in run
return orig.install.run(self)
File “/usr/local/lib/python3.5/distutils/command/install.py”, line 539, in run
self.run_command(‘build’)
File “/usr/local/lib/python3.5/distutils/cmd.py”, line 313, in run_command
self.distribution.run_command(command)
File “/usr/local/lib/python3.5/distutils/dist.py”, line 974, in run_command
cmd_obj.run()
File “/usr/local/lib/python3.5/distutils/command/build.py”, line 135, in run
self.run_command(cmd_name)
File “/usr/local/lib/python3.5/distutils/cmd.py”, line 313, in run_command
self.distribution.run_command(command)
File “/usr/local/lib/python3.5/distutils/dist.py”, line 974, in run_command
cmd_obj.run()
File “/usr/local/lib/python3.5/distutils/command/build_ext.py”, line 338, in run
self.build_extensions()
File “/tmp/pip-build-inj0l_9q/pillow/setup.py”, line 577, in build_extensions
raise RequiredDependencyException(f)
__main__.RequiredDependencyException: jpeg

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File ““, line 1, in
File “/tmp/pip-build-inj0l_9q/pillow/setup.py”, line 799, in
raise RequiredDependencyException(msg)
__main__.RequiredDependencyException:

The headers or library files could not be found for jpeg,
a required dependency when compiling Pillow from source.

Please see the install instructions at:
https://pillow.readthedocs.io/en/latest/installation.html

—————————————-
Command “/usr/local/bin/python3.5 -u -c “import setuptools, tokenize;__file__=’/tmp/pip-build-inj0l_9q/pillow/setup.py’;f=getattr(tokenize, ‘open’, open)(__file__);code=f.read().replace(‘\r\n’, ‘\n’);f.close();exec(compile(code, __file__, ‘exec’))” install –record /tmp/pip-xp_x4w_5-record/install-record.txt –single-version-externally-managed –compile” failed with error code 1 in /tmp/pip-build-inj0l_9q/pillow/

Thanks to the comment on the following Stackoverflow post for the solution: https://stackoverflow.com/a/34631976/522859

Updating to Python 3.5.1 on RaspberryPi

Hi everyone,

Just a quick post on how to update to Python 3.5.1 the normal upgrade process isn’t working for you:


cd ~
wget https://www.python.org/ftp/python/3.5.1/Python-3.5.1.tgz
tar -zxvf Python-3.5.1.tgz
cd Python-3.5.1
./configure && make && sudo make install

You may need to restart once this is complete. Run the following to confirm that the version is 3.5.1:

pi@raspberrypi:~ $ python3 --version
Python 3.5.1

Check out the following link for more info: https://stackoverflow.com/a/37079319/522859

Check Tensorflow Version – Raspbian

Hey everyone,

Just a quick post on how to check the Tensorflow version on Raspbian with a one-liner (assumes Python 3.x):


python3 -c 'import tensorflow as tf; print(tf.__version__)'

Check out this Stackoverflow post for more info: https://stackoverflow.com/a/38549357/522859

AttributeError: ‘dict’ object has no attribute ‘iteritems’ – Python

Hey everyone,

Just running through object detection samples for Tensorflow and I encountered the following error:

Sample: https://github.com/GoogleCloudPlatform/tensorflow-object-detection-example

AttributeError: ‘dict’ object has no attribute ‘iteritems’

The issue seems to be that the sample hasn’t been made compatible with Python 3.x. Simply make the following change and it should work:


# Original
for cls, new_image in new_images.iteritems():

# Changed
for cls, new_image in new_images.items():

Thanks to the following StackOverflow post: https://stackoverflow.com/a/30418498/522859

Converting proto files to .py on Windows – Tensorflow

Hey everyone,

Ran into a bit of an issue today with Tensorflow:

ImportError: cannot import name preprocessor_pb2

Turned out that I hadn’t run some of the installing steps. I needed to use protoc to convert the proto directory files:

protoc object_detection/protos/preprocessor_pb2.proto --python_out=.

This turned out to be a bit of a headache as well, but thankfully a github post explained it all pretty well:

Here are the steps I followed to install it for windows:
(Prerequisite, you must have python, pip and)

Choose a Python release from here and download: Link here
– Extract the tar.gzor zip
– Open a cmd and pip install the following: pillow, lxml, jupyter, matplotlib
– Copy the protoc.exe from the protoc folder (you don’t need to do all the CMake steps you might have stumbled upon, it worked for me without them too) and paste it into your protos folder in the object detection directory.
– Run the protoc for each of those protos like “protoc object_detection/protos/*.proto –python_out=.”. . Note that you might encounter a problem with the paths and there’s two ways around that: Either move the protoc.exe two folders down or do the noobish thing that I did – copy the protos and paste them into a new directory inside the protos folder ‘object_detection\protos’ so you would have a folder structure like’\object_detection\protos\object_detection\protos’ (If it looks stupid but it works, it’s not stupid eh?) Note that *.proto might also not work and you might have to do each of them individually
– You are done. :) Try to run something to see if you have any problems. You might have to install a manual version of numpyandscipy

GitHub Link: https://github.com/tensorflow/models/issues/1934

Check if String Contains a Substring – Python

Hey everyone,

Just a quick post on how to check if a string contains a string in python:

if "STRINGTOFIND" in "testtesttestSTRINGTOFINDtestesttest":
# continue

Thanks to this stackoverflow post: https://stackoverflow.com/a/5473023/522859

Compass Only Works on Pins 10 and 11 – Arduino/Software Serial

Hey everyone,

A bit of a confusing issue I ran into today. I couldn’t get my compass to work on any pins other than 10 or 11. Thankfully, there’s a fairly logical explanation:

Not all pins on the Mega and Mega 2560 support change interrupts, so only the following can be used for RX: 10, 11, 12, 13, 14, 15, 50, 51, 52, 53, A8 (62), A9 (63), A10 (64), A11 (65), A12 (66), A13 (67), A14 (68), A15 (69).

I ended up using pins 50 and 51 and it all worked fine. See the following links for more info:
https://www.arduino.cc/en/Reference/softwareSerial
https://arduino.stackexchange.com/a/35719/37451

UnicodeDecodeError on RaspberryPi – Python

Hey everyone,

I ran into the following error while trying to read serial input on a Raspberry Pi hooked up to an Arduino via USB:

UnicodeDecodeError: ‘utf-8’ codec can’t decode byte 0za8 in position 0: invalid start byte

The solution was as follows:

#buffer_string = ser.read().decode('utf-8')
buffer_string = ser.read().decode('utf-8', errors='replace')

Thanks to the following link: https://github.com/OpenBCI/OpenBCI_Python/issues/24