raspberry-pi on Computing Club

Outreach Raspberry Pis 2

Mon, 04 Nov 2019 11:06:02 +0000

I thought I’d better record some of the stuff I did to address these issues.

Updating Raspian from Jessie to Stretch

This was simply a matter of changing the OS version in the sources files and running an update:

sudo sed -i "s/jessie/stretch/g" /etc/apt/sources.list
sudo sed -i "s/jessie/stretch/g" /etc/apt/sources.list.d/raspi.list
sudo apt update
sudo apt -y dist-upgrade

I also had to say yes or no to some prompts about changing configuration files to the new default or keeping the old customized one.

One of the Pis had a smaller disk than the others. It was the same one that was broken (see below). That made updating more difficult as sudo apt -y dist-upgrade did not proceed due to lack of disk space. My solution was to remove the biggest package, wolfram-engine, then continue as above.

Chromium in kiosk mode

I noticed that right-click menus were appearing when people were playing NuOdyssey at Celebrate Science and that the fullscreen was somehow being exited. These problems can be avoided by running Chromium in kiosk mode, which forces fullscreen always and disables right-click. I made a desktop file to start NuOdyssey in a kiosk mode session of Chromium:

$ cat nuodyssey.desktop

[Desktop Entry]
Type=Application
Terminal=false
Exec=chromium-browser --kiosk localhost
Name=NuOdyssey
Comment=A game about neutrinos
Categories=Education;

and put it on the desktop of the Neutrino Pis.

Changing the password — when you don’t know the password

This was surprisingly easy, as the Pis are set up to run sudo without a password prompt. Simply run:

sudo passwd pi

to get a prompt to set the new password for the user pi. I have recorded the new password in the outreach document.

Disabling screen blanking

Since we’re using LightDM:

$ cat /etc/X11/default-display-manager

/usr/sbin/lightdm

edit the lightdm configuration file

sudo vim /etc/lightdm/lightdm.conf

and add

xserver-command=X -s 0 dpms

below [Seat:*] to disable screen blanking.

Fixing the dead Pi

One of the Pis stopped coming on when plugged in. The (red) power light came on, so it had power. However, the (green) SD card activity light did not come on, suggesting a problem with the SD card. I dismantled the enclosure to get access to the SD card, which is located as shown by the red square below.

On reseating the card, the Pi started working again. Good old “turn it off and on again”.

Setting hostnames

On most Pis, I noticed sudo was complaining:

sudo: unable to resolve host HOSTNAME

where I have replaced the real hostname with HOSTNAME. I noticed that /etc/hosts was not correctly configured with the right hostname, so changed it to look like:

$ cat /etc/hosts

127.0.0.1       localhost
::1             localhost ip6-localhost ip6-loopback
ff02::1         ip6-allnodes
ff02::2         ip6-allrouters

127.0.1.1       HOSTNAME

That stopped the error messages.

On the other Pis, the hostname had not been changed from the default. This makes it difficult to distinguish them, especially when accessing them by SSH. To change the hostname, I made the same change as above and also changed the hostname file so that it looked like:

$ cat /etc/hostname

HOSTNAME

Outreach Raspberry Pis

Tue, 29 Oct 2019 19:26:34 +0000

Today was the first day of Celebrate Science 2019. Whilst taking a break from running our exhibit, I had a look at our Pis.

Meet the Pis

There are nine in total.

Four have stands in the horizontal/landscape configuration. Yesterday, Henry and I found that three of these run the NuOdyssey game locally. Apparently it was written by somebody called Sunil, anybody know that story? You just start the browser which automatically brings up the game as its starting page.

The fourth horizontal one, which is visually distinguishable from the others, runs the Galton server: you interface the Pi with the Galton board via USB and it records balls passing through the light gates. I found that this all worked: it recorded the physical Galton board and graphed the results in realtime. The Galton server Pi has also been set up to remotely control the other Pis. It has scripts to remotely shutdown, reboot, and start and stop simulations. I found that this was not working, though.

The other five are in the vertical/portrait configuration and run the Galton simulation. I had noticed that one of these has nothing installed on it, so I installed the Galton simulation software on it. I decided to record the process here since it would have been very useful for such a resource to exist for me to use! And also because I’m waiting for a Pi to finish updating itself…

Getting online

Firstly, the Pis don’t seem to be able to connect the university wifi, probably because they don’t support the security protocol — maybe something we could fix by installing a new package? You can, however, log into the wifi network TheCloud@Durham - although you may have to manually navigate to //service.thecloud.net to complete login - or plug in an ethernet cable. Once online, I ran a sudo apt update && sudo apt -y full-upgrade (then reboot) for good measure. This took a long time. Then I ran sudo apt update && sudo apt install emacs vim to keep everyone happy.

Portrait mode

Next, I had to configure the Pi to operate in portrait mode. The screen can be rotated by

echo "echo rotate_display=3 >> /boot/config.txt" | sudo sh
sudo reboot

which just appends a screen rotation command to the Pi’s boot configuration file under sudo privileges and restarts the Pi. The touchscreen, however, remains configured for a landscape configuration. To fix this behaviour, I had to persistently adjust the coordinate transformation matrix for the FT5406 touch controller with

echo "xinput set-prop 'FT5406 memory based driver' 'Coordinate Transformation Matrix' 0 -1 1 1 0 0 0 0 1" >> ~/.xsessionrc
sudo reboot

It took me forever to figure that one out!

Getting the Galton code on the Pi

With all that out of the way, I could move onto installing the Galton software. I made a folder for git repos

mkdir ~/git
cd git

then cloned the GaltonBoard repo

git clone https://github.com/eidoom/GaltonBoard.git
cd GaltonBoard

and installed dependancies (recall that James has updated the software for Python 3)

sudo apt install python3 python3-numpy python3-matplotlib python3-scipy

before trying the simulation, ./galtonsim, and it worked!

I also automated the installation of the application shortcut to the desktop and application menu (with an icon), which can be run with ./install-sim.sh.

Galton board code

Mon, 21 Oct 2019 13:25:33 +0100

Ideas for improving the Galton board software

Mass of balls
Size of balls
Size of pins
Width of barriers
Fix lag
- Due to N=300?
Deploy on Pis from GitHub repo, automate updates
Get light gates working
Somehow show effect of large N
- If performance is an issue, pre-calculate
Add option to drip feed balls into simulation
Check dependencies
Add sliders to change physical parameters
Change gravity on the fly? As a vector? Accelerometers in Pis?
Maybe: allow barriers to be drawn in by hand
Consider using some more up-to-date libraries? Touch screen interactivity, GUI, physics?
Make it into a webapp? (not to replace Pi software, to provide in addition)

Plan of action

I’ve added the more pedestrian suggestions as issues on the repo.
We can assign people interested in working on these there.