*Update 29/09/13. I’m back from honeymoon and have fixed the file downloads, sorry about that, the cause was a conflict between some apps*
*Update 17/09/13. I have been informed that some people have been having trouble downloading the source code, as I’m on honeymoon at the moment I only have an iPhone so I can’t even check the link. Rest assured I will sort it when I’m back in the UK*
*Update 16/09/13. These have now been featured on hackaday. How awesome is that?!*
So the big day has finally arrived and Charlie and I are getting married! Don’t worry I’m not actually blogging from our wedding, this post has been written in advance.
I can now tell you about a little project (actually it was not-so little) we have undertaken, Charlie and I have designed and created some rather unique gifts for our bridesmaids, best man and page boy. Electron trees with their own colour cycling illuminated stands.
What is an electron tree? Also known as Lichtenberg Figures or Captured Lightning, they are what can be created by firing a beam of high energy electrons at a piece of acrylic and then striking the acrylic with a grounded stud.
The high energy electrons come to rest within the acrylic and form a plane of charge, once the grounding stud strikes the acrylic, a discharge path is created and all the electrons shoot to ground like a lightning strike, burning a path as they go.
What remains after the discharge is a block with a preserved representation of the path the charge travelled to get to ground, which as well as being an example of a fractal is a beautiful and interesting thing to behold, especially when lit up from below.
Every electron tree is completely unique and, as a linear accelerator is required to create one; they are extremely rare. As one of the clinical linear accelerators where I work was soon to be decommissioned, I had an opportunity to create some.
Most electron trees are square or rectangular, as creating other acrylic shapes is labour intensive and time consuming. But, after finding some acrylic contact juggling balls on eBay; we decided spherical electron trees would be the way to go. We couldn’t think of anything better to give to the people taking part in our special day!
Making the Stand
To best present our gifts we knew we would need a light up stand on which to mount them, and so we headed to Southerndown Beach, near Cardiff; a location Doctor Who fans will know as Bad Wolf Bay. Our objective: hunt down a piece of driftwood that could be crafted into stands for our unique gifts.
After spending a few hours hunting for a decent piece, and watching people walk past in the other direction having found some great lumps of wood themselves, we started to think we would never find anything usable, then we found a piece of tree that wasn’t quite what we were after, but it might do the job.
However, once I started to chop up this log into smaller, usable chunks, I couldn’t believe our luck! The wood had some lovely, colourful spalting running through it, and would make a very attractive set of stands.
The Technical Bit
For the lighting, I decided to use three colours of ultra-bright LED’s, each fading in and out in sequence to create a host of different colours as they mix in different ratios. In order to achieve the fading effect I decided to use Pulse Width Modulation (PWM).
For this application I found the PIC12F1501 Microcontroller; a small 8 pin, relatively new addition to Microchip’s collection with 4 PWM outputs, as well as an amazing amount of further features for such a small chip.
I also decided to add a push-button to allow the user to pause the cycling colours on their favourite, and resume the cycle at any time.
I programmed the microcontroller in assembler using Microchip MPLAB and designed the circuit board using Designspark PCB, in order to save space and make a board small enough to fit in the stand I mounted the LED’s on the solder side. I used a mini USB socket as a power input.
If any of you would like to replicate these electronics, or create your own take on them, please find the associated files available for download below.
Here are some video’s of the making of the electron trees, stand and electronics, for those of you who aren’t bored out of their skulls yet.