A magic wand.
On September 9-10, 2006, the Hogwarts and the Draconian Prohecy game was run by Snout. One aspect of the game was casting spells on a magic wand which each team received. This page describes the magic wand and how it was created.
Be sure to check out the Wand FAQ too for interesting wand facts.
Note: if you are looking for the page that used to be here, it has been split into the following pages:
The wand is a magical device for casting spells. Spells are cast by either waving the wand around or tapping the wand on a hard surface.
Waving spells use motions called Mwanemes. Mwanemes and spellcasting are described in the textbook and also on the Spell Casting Page. There is a complete list of spells in the wand here.
Tapping spells are rythm spells (aka song spells). The spell is cast by tapping a song out using the wand as a drumstick. To get a complete list of songs that the wand recognizes cast the "hello" spell (you can also check the wand sourcecode).
When a spell is successfully cast on the wand, the wand replies with a message. Messages are viewed by waving the wand quickly back and forth in front of you. Glowing gems display the message in red letters in midair.
After Snout decided to run the Hogwarts and the Draconian Prophecy game Acorn came up with the idea for the wand. For a previous game, Justice Unlimited, Acorn and Cary created the DRUID and the Bat Blinker. The wand is inspired by these two devices.
In January, 2006, Acorn built a prototype for the wand and began working on software. Team Snout had the goal to have some sort of spell casting as part of the game, so when Acorn presented the early wand prototype to the group in February it was well received.
The text display is similar to the display on the Bat Blinker. One of the problems with the Bat Blinker is that the text does not always show up in the same place. The Bat Blinker uses a "gravity switch" made out of a spring and a ball of solder which contacts a plate of copper at the bottom of the loop. One way to make this more reliable is to incorportate an accelerometer to measure the force on the spinning or waving object. That way the text can be made to start accurately in the same location at the start of each wave of the wand. Accelerometers are expensive and seemed tricky to work with, so using one to control the text seemed like overkill. However, if the accelerometer could also be used to recognize spell-casting gestures then the accelerometer would be well worth it!
Since Acorn had no idea how to do gesture recognition he had a lot of experimenting to do. Lots of time was spent waving the wand prototype around and looking at the data from the accelermeter. Acorn's wg (wand graphing) program was used to visually examine the data.
In the late spring it became apparent that the waving spells might not ever work. Snout decided that we better come up with an easier way to cast spells if we were to rely on being able to use the wand in the game. Acorn came up with the "song spell" idea which leveraged the electronics and software already working in the wand. When the wand is tapped against a hard surface the output of the accelerometer is very distinctive. Therefore taps are easy to detect. The program which takes the tap timing and decides which song has been tapped out was written in a week or two. At that point the rest of Snout could relax, knowing that the wand was working well enough that it could be used in the game. Then Acorn went back to work on the waving spells.
The waving spell recognizer was written in C. It went through many iterations of tuning, but finally was working well enough that it could distinguish one spell from another. Acorn is too cheap to buy a C compiler for the Microchip PIC18lf2620 microcontroller that was used in the wand (e.g. $175 for the one from CCS Inc) so the next step was to re-code the algorithm in assembly and get it working on the wand itself. This was finally completed about 3 weeks before the game (4 days before the dry run).
The first 5 wands, which were used in the dry run, were built by Acorn. The case design was not yet complete so these wands were simply wrapped in electrical tape.
The wands used in the actual game weekend were built by a group of people over several nights at the Treehouse (Acorn's place). Special thanks to Cary and the two mystery solderers (whose names I am trying to remeber) who showed up and assembled much of the wand electronics for many of the wands. The plan was to build around 25-30 wands so that there would be extras. By the time the game started we had only 17 working wands - not quite the surplus we were hoping for! In the last Defense against the Dark Arts class the TA (professor Oaknut) actually helped teach the class using a non working dummy wand!
The case for the wand was created using "Sculpey" clay over a non-working wand skelaton. Curtis created the final shape. A silicon rubber mold was made and the final wands were cast in plastic with the electronics embedded right in the plastic as it hardened. As the wands came out of the mold on Friday, Sept 8, they were painted by Crissy Gugler and Lisa Long.
The wand is an electronic gadget which contains (among other things) an accelerometer, a microcontroller, and 5 red LEDs.
The design and construction can be broken down into the following steps:
Follow the links above to learn how each part of the wand works. I have tried to include enough information so that it is possible for the reader to build their own wand. I am placing the sourcecode and design under GPL so you are free to use it under those terms. You can download the sourcecode for the wand (including the printed circuit board design) here:
Check out the Wand FAQ which has many questions and answers about the wand.
You can also ask me, Acorn, on the feedback page. Feel free to ask about how the wand works, how you can build your own, about the Hogwarts game, or anything else for that matter!
One way to get a wand is to build it yourself. All the information you need is contained in the "How does the wand work?" section. Also the following files contain all the information needed to build the circuit board and compile the software:
I am also considering offering a kit. The cost and availability will be based on how much interest there is. If you are interested in buying a kit please fill out the feedback form and be sure to mention that you are interested in a kit. It will probably be in the $30-$50 range, also depending on level of interest (parts are cheaper in bulk).
This file Copyright (C) 2006 by Nathan (Acorn) Pooley
Go to TOP Wand page
Go to Acorn's personal webpage
Go to Hogwarts website: www.gotohogwarts.com
Snout: www.snout.org/game
WarTron B.I.T.E. website
Gadgets of Justice Unlimited website
File created by Acorn on Sat Sep 16, 2006