Stephen C Phillips (Posts about Python)

Getting a Python script to run in the background (as a service) on boot

Stephen C Phillips — Sun, 21 Jul 2013 13:05:28 GMT

Getting a Python script to run in the background (as a service) on boot

For some of my projects I write a simple service in Python and need it to start running in the background when the Raspberry Pi boots. Different Linux distributions use different ways of starting and stopping services (some now use Upstart, some systemd). I am using the "Wheezy" Debian distribution on my Raspberry Pi, and in this case the proper way to do this is using an "init script". These are stored in the /etc/init.d folder. In there you can find scripts that for instance, start the networking system or a print server. Debian Wheezy uses the old Sys V init system which means that these scripts are run according to symbolic links in the /etc/rc.x directories. The Debian documentation explains this.

European public holiday leaderboard

Stephen C Phillips — Tue, 01 Jan 2013 12:29:49 GMT

European public holiday leaderboard

I work in a lot of European projects. This means that we often have weekly teleconferences across several countries which are often scuppered by a partner or partners being on holiday because of a national holiday. In the UK, all our public holidays are put on Mondays (with some Fridays) so that you don't get the country shutting down in the middle of the week. In other countries the public holidays (e.g. saints' days) just land on the same date every year with two results:

Sometimes they land on a weekend so most people don't actually get a holiday.
When they land on a Tuesday or a Thursday lots of people take off the Monday or Friday as well to make a really long weekend and you lose almost half a week.

Moving the Where Clock from a web browser

Stephen C Phillips — Thu, 27 Dec 2012 15:39:12 GMT

Moving the Where Clock from a web browser

Now I've got a web server and I've got code to control the stepper motor, let's put them together and control the stepper motor from a web browser! Here's the new code: clockServer.py.

A simple Python webserver

Stephen C Phillips — Thu, 27 Dec 2012 10:38:55 GMT

A simple Python webserver

Now I can control the stepper-motor from Python I need to be able to tell the Raspberry Pi to move the motor from my phone so that, for instance, when I get to work it can tell the motor to move the indicator hand to point to "Work".

To do this, the easiest way seem to me to be using a web server on the Pi. I want to make it so that if you GET the URL http://<raspberry.server>:8080/move?a=90 then it will move the hand to 90 degrees. This normally requires a web server and a CGI script but it seemed overkill to install Apache or even something lighter-weight such as lighttpd or nginx for such a simple task so I've written my own: much more interesting!

A Python class to move the stepper motor

Stephen C Phillips — Wed, 26 Dec 2012 23:40:27 GMT

A Python class to move the stepper motor

To properly control the stepper motor from the Raspberry Pi we need a class to represent it. This is one of the most direct ways of understanding object oriented programming (OOP): from the class you make an "object" and the object represents and controls an object in the real world (the stepper motor).

The class lets us remember (and control) all the information we need:

the pins the motor is connected on;
the speed of the motor;
the angle the motor is currently pointing to.

Wiring done right

Stephen C Phillips — Mon, 24 Dec 2012 14:16:42 GMT

Wiring Done Right

With the new jumper leads from eBay I wired it all up again. For the power, the motor controller board has 4 pins and I don't know why. Two of them are bridged by a jumper and by the other two there is a "-" and a "+" and "5-12V" underneath. I wired the 5V pin of the Pi (P2) to the one labelled "+" and the ground pin of the Pi (P1) to the "-". Seems to work, but I don't know if I just got lucky or whether it doesn't matter which way round you put them.

For the controller lines I wired P18, P22, P24 and P26 to IN1, IN2, IN3 and IN4 respectively. That done, I turned it on and tried some software.