Complete on{X} script to control the Where Clock

After a lot of head scratching I’ve finished the on{X} script to control the Where Clock: making it turn around when I enter or leave places. Here it is:

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Using on{X} to Control the Where Clock

I want to be able to send GET requests to the web server on my Raspberry Pi from my phone so that I can have the hand of the Where Clock turn to point at where I am or what I’m doing.

Of course, I can fire up a web browser on my phone and type in the URL of the Pi’s web server but that’s a little inconvenient: it needs to be automatic, driven by my location or other events. That’s where an interesting project from Microsoft comes in: on{X}. You go to that site and sign in with Facebook, download an app to your Android phone and again associate it with Facebook and then, on the web site, you can write little scripts using JavaScript which get sent to your phone and run there.

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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.

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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!

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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.

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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.

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Stepper Motor

To make the Where Clock I need a stepper motors. I don’t know how stepper motors work but I know you can get them to turn around to point in a particular direction. Of course, I’m not the first person to think of this and after a bit of Googling I found a page about using stepper-motors from a Raspberry Pi.

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The Start of Something

I’ve been thinking about having a blog for a long time as a place to put information that other people might find useful. Finally I’ve got one (it is very easy to set up thanks to my host, Webfaction). I suppose I finally thought I had something interesting enough to share.

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