Thursday, 20 December 2012

Raspberry Pi Cardboard Box

Another case design. Made from an old manila folder so that's recycling too!

Wednesday, 19 December 2012

Raspberry Pi Guinness Grotto!

This is a simple little project with a great back-story.

About 15 years ago, my late father David Walsh was having a pint in the Ormeau Arms, a.k.a. Fealty's, bar on High Street in Bangor.  This was his local and by then the only bar left in Bangor that you could take a dog into.  I remember seeing them put an ashtray on the floor with some beer in it for the dogs.  Anyway it was Christmas time and there was a big tree behind the bar with a string of these promotional Guinness Christmas lights on it.  My da pestered the barman until they gave him one of the Guinness glass shades and it became a family in-joke on the Christmas tree at my mother's house every year.

With my father and then my mother passing and clearing the house, the Guinness glass went missing until last week when I found it in amongst some spare bulbs for a long-gone string of lights.

It needed a 21st century upgrade!

The RaspberryPi is on the left, connected with my home-made GPIO connector to a breadboard, ULN2003 buffer chip and a whole heap of LEDs.  There are 3 LEDs inside the Guinness glass, one red, one orange and a bright white one.  The string of LEDs round the glass is set up to run on 5 volts.

The whole gizmo is programmed in Python and cycles through the 3 LEDs inside the glass to get a range of colours and then stuns you with the string of white lights coming on.

I tried to video it in action, but it was too dark for the 'phone camera, so I just took a few still shots of it and this is the best one.

So this is to you dad for giving me an acquiring mind and a love of anything electrical or mechanical and often both and for solving problems the lateral, interesting way.

"Made of more."

Sunday, 16 December 2012

RaspberryPi I2C Level Shifter

A small project, but vital when you're experimenting with the RaspberryPi because the RPi's General Purpose Input Output (GPIO) pins operate at 3.3v rather than 5v.  There are several ways around this and I'm using a ULN2003 chip at the moment to play with the GPIO in output mode, but for I2C bus experiments, the ports are bi-directional, so the level-shifter needs to work both ways too.

The circuit is a novel application of a MOSFET, in this case a BSS144 to provide a bi-directional level-shift circuit.  I'd used the same approach once before to connect a 3.3v serial USB module to a PIC microcontroller operating at 5v TTL levels, which worked fine, but I wanted a design for a reproducible and reusable module that can be plugged into a breadboard.

The only problem with the design (for me) is that the BSS144 is a tiny surface-mount component and is easy to lose so a fine-tipped soldering iron, a good magnifier and pair of tweezers are the order of the day.

This is my stripboard design, viewed from the copper strip side ('bottom') of the board.  It could be made a bit smaller, but as it is a prototype, I left an extra track at the top and bottom and an extra column of holes at each side.  The connections for the I2C buses are made with gold-plated pin strips (in this case salvaged from a broken satellite receiver).  The GND connections are really not necessary and are there for the sake of consistency, but do not need to be connected.

As you can see, the BSS144 MOSFETs are very small and a minimum of heat should be applied to solder them to the board.  The copper strips under the two MOSFETs are cut with a sharp knife rather than using a pin drill.

This is the finished and tested module using extra long pin strips salvaged from a broken satellite receiver.  I'm going to put some heat-shrink sleeve over the two resistors so they can be safely folded flat to the board and then insulate the top and bottom of the module with insulating tape and finally put a sticker on to label the connections for easy reference.

I'll probably make a couple more of these as I can see them becoming very handy.

Sunday, 9 December 2012

DIY Arduino

A few weeks ago I finally got around to buying an Arduino microcontroller board.  There's no doubt this is the easiest way to get into microcontrollers for beginners and all of the software and hardware designs are open source, how cool is that?  Pretty quickly I found a video output library for the Arduino and have been experimenting with that as it would make a great basis for a retro video display.  I wanted to see about building a standalone video generator that would connect as a module to other microcontrollers via either RS232 or maybe as a slave I2C device.  I purchased a DIY Arduino kit for 8 GBP on eBay, basically just an AT MEGA 328 microcontroller with the serial bootloader pre-loaded and a USB-to-TTL RS232 adaptor.  This is it breadboarded and almost ready to connect to a video monitor, except I had unexpected problems with compiling the TV-OUT sketch (script, program) on my Linux workshop machine.  It worked okay on Windows, so I'll need to investigate this further.

UPDATE - Got the AT328 programmed and running the TV Out demo sketch sucessfully.

I'm writing this post on a Scroll Essential 7" tablet running Android 4.0 and a neat little case/keyboard to speed up the typing.  Total cost, under 100 GBP.

Saturday, 1 December 2012

Pringles Tin Speakers

During the summer, Pringles crisps were giving away free speakers that clip on the top of an empty Pringles tin.  The only drawback was that for a stereo pair I'd have needed to eat my way through 6 boxes of Pringles, and I'm more of a Tayto guy myself.  Anyway, we went to see 'Skyfall' last month and my 13-year-old darling daughter got me to buy her 2 of the small cartons of Pringles for the film (costing about as much as 6 big tins in Asda!).  I hung onto the empty boxes and discovered that a pair of speakers I had reclaimed from some old thing were a perfect fit for the Pringles tins.  I soldered lengths of twin speaker cable to them and glued them onto the top of the tins with epoxy.  To round them off I found some 'funky foam' in my son's craft box (I owe him a sheet now) and covered them with it.  They sound amazingly good considering what they are and they look pretty contemporary too.

So I was good to go and the mini CD player I was going to use them with died.  Typical.

If you've never heard of Tayto, well basically Tayto Cheese and Onion are the best crisps ever made.