This afternoon I was without anything to do when I remembered my DK421 project, which had been shoved off into a dusty corner of my hard drive. I didn’t feel like programming any, and wouldn’t know what to do or add anyway, so I got into the hardware side of it.

The Sheets

I dug into Stephanies old room and found the keyboard from the green dinosaur, an Acer computer from the early-90’s. Anyway, I found it, took it to my room and cracked it open. Very simple device really. The keypresses are captured by switches composed of two sheets of plastic, very similar to slide-projector transparency sheets, with tracing on them. When you press the key it compresses a rubber bubble in a sheet and smashes the air, and thus the switch, down and completes the circuit. These connections go to a board with some leds and a chip for translating them into whatever goes down that PS2 cable.

I imagine that a newer keyboard might be more complicated, at least if it’s usb. Maybe not though. I only have so many keyboards to rip open.

Following the tearing apart of the keyboard I hooked it up to my old gateway laptop (it’s the computer I care the least about) and fired it up. No lights, no response. I shut it back down and figured out that I hadn’t reconnected a little black ground that had been hooked onto the metal mounting board as well as one of the pins. If you look at the picture of the transparency-stuff circuit you can see that one pin is connected only to a big spot for the ground.

The Pins

I taped it up and got it working right off the bat. Shiny. I then taped it onto the laptop in the lovely testing position illustrated here. I got a piece of thick copper wire, off of an old power supply, and generously stripped the ends (okay, my father did for me), 1.5″ at least, then coiled each end around a long finishing nail (that’s what it said on the box) and taped it up. This made for a nice, easy to control point-to-point connector for me.

With my newly created tool I fired up VIM and started shorting the pins together to see what they wrote. Okay, thats not true. First I tried tracing individual keys on the transparent stuff, but that got old real fast. It is, however, necessary for finding keys like shift. Regardless, I tried out the good old hunt and peck method, and soon had a list with more than enough keys for the drum triggers. I then tried out the shift key with a piece of spare wire, it works great. Thats an important one, because it is needed for the high-hat pedal.

The Shift Key

Well, thats enough for now. Hopefully the pictures shed some light on the matter if it’s still fuzzy. I haven’t made up my mind on what to build the triggers out of. I almost want to go the air pressure route so the switches won’t wear out to fast. I’ll also have to consider how to build and mount all this, I’m thinking PVC at this point. Off to a good start though :)

I’ve been working on my DrumKit again, since I don’t get to play with my Nokia 770. I came up with a better name for this revision, DK421. It doesn’t mean anything. Well, it kinda does. It came from a Stormtrooper in ANH (”TK421, Why aren’t you at your post? TK421, respond.”)

There isn’t a lot of change in this version. I re-read the API for javax.sound.sampled and re-wrote the SoundClip class (formerly KitClip) from scratch. It think it’s cleaner and more usefull for other projects now.

I also added in a file chooser class, DrumChooser so there aren’t any absolute paths in the source anymore. I also added to that class a minor key-fetching function. I hope to make the kit’s expandable, as many drums as you can until you hit a LineUnavailableException.

The GUI hasn’t changed a lick, and I need to clean it up and develop a new layout for it and for the “multiple-drum” expandable version. It’s surprising what you can learn from an API.

I finally started work on my DrumKit project today. Essentially this is an attempt to create a electronic drum set from some pads, an old keyboard and a computer. I got down to buisness and wrote up a Java app that plays back the drum sounds on key press events. It filters them and even handles shift for the hi-hat open/close, which I’ll use to make the hi-hat pedal work.

The source is messy, and still has relative path’s for the sound files. Essentially it’s a frame, a keylistener and some clips. Not too rough, though patching this together from the Java API and sparse information on javax.sound.sampled was tougher than I guessed it would be. Anyway, it’s got some bugs and features not implemented, but I can play drums with my keyboard now, which is a good start.

The Cutting Edge DrumKit GUI

I suppose I should upload the code just in case, and to keep track of my versions. You can get the source and the sounds for Version 0.01 below. As a heads up, all the kit samples are absolute path’d for my machine, so you’ll need to adjust them if you intend to compile it.
» DrumKit001.tar.gz - Everything
» DrumKit.java - Main class
» KeyHandler.java - Event listener
» KitClip.java - Kit sample class