Saturday, 30 June 2012

Raspberry day 1

Download Debian squeeze image
Download Win32Disk imager
It's a very basic program which for some odd reason is written in QT, copy the squeeze image onto the SD using the imager program. All prior contents of your SD will be lost.
Next we need to create a config.txt file to set up the overscan on the composite video.
overscan_left=20
overscan_right=0
overscan_top=0overscan_bottom=0

Linux for Beginners on Raspberry Pi
So by now, this starts to make sense? No, well these are my notes on unboxing my pi, written from the perspective of a Windows user. Don't get me wrong, I know how to read bash instructions, and how to type in the wierd runes that pass for commands. But I recall and understand almost none of them. So if you find my notes remotely usefull, and what I am showing interesting, do not bother to ask how it works. I probably don't have that good an explanation of them. If however you are struggling too, read on.

The debian squeeze credentials are pi and raspberry. Neat.
We will be learning to use the console, not because I am old school, but because my intention is not graphic art, it's to learn something new. For now we are not going to strip out the desktop, so you can add and enable a desktop later if you like. My plan is to have 2 "roms" or SD cards if you like for separate pi personalities, and once I have a proper screen a desktop would be nice. Graphics look terrible over composite video though.
Beginners guide to using Nano
Next, we want to install an ssh server, if like me you are trying to read the text over a composite cable plugged into your telly, you want to SSH in and control your pi from a crisp LCD screen. Type:
ifconfig

The pi will display it's IP address, take a note of it. That;s where we will neet to connect to using ssh.
Before we do that, let me recall my setup.
Hardware
  1. Raspberry Pi powered off USB cable from my desktop machine (you can power it off your android charger too).
  2. Composite video - that's the RCA plug into the telly, which is a pretty old one which I did not pay for.
  3. Network ethernet - directly into my router for now, wifi later.
  4. Mini keyboard - get a small keyboard.
  5. USB hub, a 4-port one. Basic 4-port hub, ideally I want to get a self-powered one that takes 5v supply.
  6. Mouse, get a small one. It's probably not needed though.
Keyboard:You can get ones intended for mobiles, those are too fiddly, one that's 30cm or 12 inches wide is still small, lightweight and easy for "kids" to use while on the move.
USB hub: the pi will eventually need wifi, so we will run out of ports fast, once we add a serial port ,wifi dongle etc into the mix here.
Video: In case you are wondering, I do not have a HDMI monitor, and active converters (passives do not work) actually cost more than a monitor does anyway.

OK, SSH Setup

Download putty for Windows, drop it onto your desktop and run it, you should get a connection refused though, yeah wise guy.
The next thing I still need to figure out is root access so I don't have to type sudo (Super User Do) all of the time, but now we need to install ssh.
sudo apt-get update
sudo apt-get install open-sshserver
And optionally start the service up.
service ssh start

Now try to connect from putty - just use the reconnect or duplicate-session menu option in putty. It will prompt you to accept the public key from the pi. Now at this time, I am assuming the ssh install routine generated a fresh key, else everyone would have the same key in the world, so it's pretty safe to accept this fingerprint now. Putty will store it for next time we connect.

Once we reboot the Pi, you will not need to start ssh server again. Try this:
sudo reboot -f
And then wait for it to finish booting before trying again. If all fails, try uninstall
sudo apt-get remove --purge ssh
So lets get onto editing configuration files.
Bootup configuration, Squeeze on your Raspberry Pi


We are using Debian Squeeze, and here I want to point out a few things about the filesystem, which I will save the details of for someone else, but suffice to say the /boot/config.txt file is actually not "in" the filesystem, it lives on the root of the SD card.
So you can edit this arm config file from nano, or directly on your Windows computer using notepad.exe . The processor boot code reads this file off of the SD card before the gnu-linux system starts, in order to set up the video.

Following up will be something on powering the pi using a sustainable energy source, how to configure services and networking, and root access to the system.

Saturday, 16 June 2012

Dissecting a Golf Ball

As part of the year-long science week I have undertaken (I started about 2 years ago I think) I am going to unveil what it is that makes a golf ball go quite as far as they do these days.Click on the linky below to see for yourself what's inside coutesy of someone who has done this in a slightly-scientific way.

Larissa's blog: Looking Glass Self: Dissecting a Golf Ball: Mosey is a chewing machine.  Today, I was resting on the couch and Mosey was chewing on a golf ball.  Suddenly I heard this crackling, explo...

That's pretty much a vignette of part 1, my version however involves a series of youtube videos. We explore what might be inside a golf ball. If you clicked on Larissa's link, you will spoil the videos which start here.

Part 2 is the math and sciencey part, around how the rubber stores energy at the point it is struck, and turns that energy efficiently into a flight, aided by the dimples on the ball. The dimples create an air-pocket system around the ball, that reduces turbulence and in fact carries the ball further than if it were just smooth on the outside.