Showing posts with label java developer to raspberry pi rookie. Show all posts

Raspberry Pi: Let's light up the (hello) world

There's a light, that shines, special for you, and me..


Soldering complete and Occidentalis installed, it is time to start learning how all this stuff works. Plus check that my soldering isn't so bad that it has destroyed my Cobbler.

From a quick bit of googling I started with the HelloWorld project:

Hello World: Python

So there are a tonne of hello world pythons tutorials and examples, so I won't dwell on this.
  1. from the shell (I setup wifi connection & then ssh on to the Pi so I can work from my normal desktop - I also installed vim - you can either install vim or use your preferred editor) run: 

        vim helloworld.py

    In the editor enter the following:
        print("Hello World")

    Exit and save the file (:wq)
  2. From the command line run
        sudo python helloworld.py
That's it. You will see the Hello World output in the shell. Yay.


Hello World with Lights On

So, the above was trivially easy and kinda pointless - but I did actually go through that, really just to make sure python was behaving and so I had a working baseline to go from.

So next I wanted to do a Hello World equivalent with hardware - the simplest thing to do seemed like a script that instead of printed hello world, just switched on a light briefly.

This assumes you have followed the same path as me and have opted for Occidentalis, and have soldered your Pi Cobbler (the basics are still really the same even if not using a cobbler, and are just breaking out your pi using a GPIO ribbon cable).



  1. If you opted not to install the Occidentalis OS (mod'd Wheezy OS packaged with stuff if you are planning on doing hardware stuff), then you will need to install some extra bits and pieces (you may already have them installed anyway, but running this won't do any harm - will just print the message saying its already there):
        sudo apt-get install python-dev
        sudo apt-get install python-pip
            sudo pip install RPi.GPIO
  2. Connect your Pi to the cobbler using the provided ribbon cable - plug the cobbler into your breadboard so it straddles the break down the middle (See photo below of the final setup of my breadboard for this experiment)
  3. Using a standard jumper lead, connect the ground on the cobbler to the -ve power rail on the breadboard (in this case mine is the purple-ish rail as you can see in the photo, the ground on the cobbler will be labelled GND). This is always best practice.
  4. Connect a resistor from the Pi Cobbler plug 23 to one of the free holes not linked to the cobbler (the resistor is needed to reduce the power - without one of these you will just blow your LEDs)
  5. Connect the +ve leg of the LED (the longer of the two legs) to the -ve power rail that we plugged the GND into, and the shorter LED leg into a hole in line with the resistor we plugged in (again, see photo below for final setup - although ignore the surplus resistor - that's not doing anything, I juts forgot to remove for the photo)



Now that the hardware is all connected, we need to update our simple helloworld script to control the light.  So again, run vim hellolightworld.py and enter the following script:


Now save and exit that script, then go to the shell and run python hellolightworld.py  and watch that little sucker flicker on briefly!
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Raspberry Pi & Adafruit Cobbler: Getting Started

It's yours, the world in the palm of your hand..


As mentioned last time, I had to get my hands dirty and do some soldering. Having not really done soldering since my early teens, and even then , I can't really remember what or why I was soldering. I just remember having a consciousness of what soldering was and the experience.  Anyway, needless to say, I was pretty useless at it - not helped by the fact that I was using a soldering iron from the 70's that was undoubtedly designed to fix washing machines, and solder itself to match. The pins on the Cobbler were actually closer together than the diameter of the solder i started with, which made things pretty hard for precision soldering.

To give you an idea of the size of the cobbler, here is a photo pre-assembly:


I bought the Adafruit Pi Cobbler to make prototyping easier, and a lot of the tutorials/articles around the web suggested they were a good idea, and being an electronics rookie I dutifully did what I was told.
I also noticed when I was in Maplins recently that there is now a slightly cheaper version of the cobbler available, I don't know about its quality but in shape/size/design it looks pretty similar to the Adafruit cobbler. The advantage of this is you can just stroll into your local maplin and grab one for not much more than a fiver (that is five english pounds). The red one above is the non-branded one, the blue one is the Adafruit version.

After almost doing irreparable damage to the cobbler with my antique soldering iron and solder, I also resorted to a cheap hobbyist soldering iron and solder from Maplin. It cost less than a tenner (£10) and made a huge difference. Not drinking whisky whilst soldering on the second run possibly also made a difference as well, but that theory would need to be further tested.


All in all, it took me about two-three hours, over two evenings to get the thing soldered (there are 52 pins that need soldering), and considering I haven't soldered for probably 15-20 years (and that was as a young boy, so probably just soldering wires ends with my dad or something) it went reasonably well.


Lessons Learned

1. Don't use solder/soldering irons from the 70's. Washing machine repair evidently requires less precision that modern electronics
2. Don't drink whisky whilst soldering (not proven, but I definitely saw a decline in soldering quality on the first night).
3. Soldering irons get hot - touching them to test if they have cooled down/heated up is not advised.
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Raspberry Pi: My Shopping List for getting started

As mentioned, I am completely new to electronics stuff really so I have been trying to get everything sorted and ready to get started. Coming from a Java/JVM dev background, I'm going to try and write up my experiences and things I think are different/difficult etc.

One of the first thing I did, having read a fair few tutorials/blogs on the topic, was work out all the components I needed/wanted to buy. Most of the components are really cheap, and I really didn't want to be caught short mid-development finding out I had to go out and buy something (a luxury that never happens with my usual development process - the most I have to do is go on the web and look for something).

Before I get started, here are the things I bought, which might be useful if planning on following the other posts.

They are all amazon affiliates links - which means if you buy via these links amazon gives me some cash, but won't cost you anything.

 
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