Monday, August 10, 2009

"Kill bar" guitar finished- Real guitar with Guitar Hero strum bar for killswitch

I had this idea a really long time ago and when we suddenly found out we had the extra parts lying around we decided to build it. This is for people like me who enjoy playing guitar and enjoy playing Guitar Hero. Its functions just like a normal guitar, but a strum bar from a Guitar Hero controller was wired into it and it serves as a killswitch.
For those of you who don't know, a killswitch is a function of a guitar that lets you rapidly turn the signal on and off, making a choppy sound. You can do this either by turning one pickup on and one off and rapidly switching between them with the pickup selector, or by wiring in your own button that shorts out the signal to "kill" it.
Usually a killswitch is just a button; pressing it kills the signal. To play rapidly you have to be able to press and depress the button really fast, and I had the idea of using a strum bar from a Guitar Hero controller as a sweet joke and a really useful killswitch. Unlike normal killswitches that you can only press in over and over, you can strum up and down with the strum bar which allows whoever's playing the guitar to killswitch incomprehensably faster than anyone else, to the point that you can't even discern pitch. Of course, you can also just strum down with your thumb on the bar for the classic killswitch sound.
And now... MAKING OF!
DISCLAIMER: These pictures are click-for-huge, but they all look pretty awful when magnified that much. That's what you get when you're trying to archive stuff and all you've got is an iPhone.

This is the strum bar from a wireless RedOctane Guitar Hero controller for Playstation 2. I had since moved on to 360 and this controller was pretty much useless since I had the infinietly superior SG style lying around, so I did what any nerd worth is own soldering iron would do and tore it apart.
The design of the strum bar is exceedingly simple: the bar is a plastic thing that sits on a couple pillars and as you push it up or down a pair of feet hit one of the switches seen in the above photo, detecting whether an up-strum or a down-strum (how else do you think it could tell to let you navigate menus, magic?) The electronic part of this project would be super easy because a killswitch is only a switch that shorts out the signal in a guitar. All I have to do is solder the switches on the little circuit board like I would any other switch and viola, easy killswitch. For simplicity's sake we're keeping the entire board in one piece for the project, since it's full of convinient mounting holes for the bar support and screw wells and, well, it's got switches lined up and soldered to it already! The only challenge will be cutting up the guitar to mount the board inside.
Lucky for us, the guitar, a 1983-86 Peavy Patriot, had a giant cavity already routed into it, even though the only component was a volume knob. We did some simple measurements (CRAM BOARD INSIDE, FIT GOOD) and set about making ultra-sure we'd cut the right size hole for the strum bar to poke through.
First we cut into the nearest heavy paper we could find (the box from an Adams Family VHS, classy) and slowly adjusted until the size was just right. We kept the piece as a template for our other cuts.
That tiny hammer is useless. Seriously, there isn't a single task on this earth it would be suitable for, except for posing for strange building pictures for the point of misleading people who don't read these explanatory paragraphs.
Using our paper template, we cut a slot into some real wood estimated to be the same thickness of the part of the guitar we're cutting up. We ran into our first problems here. On an Guitar Hero controller, the strum bar comes up a little out of the case and remains in place because the plastic case bumps up to allow room for the plastic "wings" that stick out to either side and rest on the support columns, allowing the waggling motion. Without it the strum bar doesn't stick out as far, but that isn't the problem. The problem was in the width of the slot. We cut it to just the right size for the strum bar, but since it doesn't stick out as far as far in our design there's a small width gain as it moves in either direction, causing it to stick because the plastic piece continues to get wider after going under the surface. If we cut the hole wide enough to avoid this there would be an awkward empty space on either side that only disappeared when the strum bar was all the way in one direction. We fixed this problem by filing the walls of the cut at an angle to allow some wiggle room and avoid sticking.
This is the board connected to our practice-wood photographed for maximum disorienting value. We drilled screw holes without measuring and as a result it was a terrible fit. That was to be expected though, we were just making sure the board would connect in the way we wanted.

Here's our cut into the guitar finally. We cut holes in the corners and then squared it out with a coping saw and finally getting it nice and smooth with files. We superglued our Adams Family-based template to the guitar as a guide.

Here's the first try at inserting the strum bar through the slot we cut. It works! But we still need to get a way to make it stick in the guitar instead of just floating there. We decided to use the screw wells that were cut into the strum bar's support columns. They connected everything together, so it would make a pretty easy connection to the guitar as well. We went out and got some much longer screws so they would reach as far as we needed and got to drilling. As we held the board in place, we found there was no good way to mark the spots where we needed to drill, as the surface was too rough to make scratches recognizeable and pencils were too wide. We solved this by burning a pencil away and sticking the graphite rods through the screw well.

Useful science: if you set a pencil on fire you will be left with an intact graphite rod.
With our drilling locations properly marked, we got to drilling and it was a perfect fit. We had to adjust the height a little to keep the strum bar from sticking, and the end result feels just like a Guitar Hero controller. On to wiring.
Here's the board connected to the guitar looking way more complex that it actually is. All those components are from its past life and we'll just be soldering to the two switches in the middle, leaving the other parts in place to make it look more impressive.
A close-up. As you can see, we drilled through the front of the guitar and all the way through the other side of the board, holding things in place with nuts.
Here's the board soldered to the volume knob. Again it looks way more complicated than it is. You can see in the bottom right that we found out the board gets in the way of the output jack a little bit, so we cut a notch into the board. The signal goes from the pickups (out the little hole in the upper-left of the board) and connects directly to the switches that are activated by the strum bar, then to the volume potentiometer and finally to the output jack. The killswitch works by connecting the positive and negative signal when a switch is pressed, causing them to cancel each other out and resulting in silence as long as the switch is pressed.
And here is a demo video:

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