Rich's Edrum Page
An electronic drum generally consists of a drum head or pad thats fitted with a triggering device that senses when the drum is hit. The trigger signal is processed by electronics which causes a drum sound to be played in response to the trigger. Commercial edrum kits and processors are made by Roland, Yamaha etc. If you are mechanically and electronically handy you can make a good set of electronic drums for a fraction of the cost of the commercial units.
My approach was to design a simple edrum pad first. I then designed a trigger to MIDI interface to which I could hook up my pads as inputs and use the MIDI output to talk to a computer. I use a Sound Blaster Live card which has a MIDI interface and provides high quality sound with relatively low latency. There are loads of sounds available for it in the soundfont format and I've found some really excellent drum soundfonts. You can customize the soundfonts using Creative's Vienna soundfont editor which is free.
My Pad Design
Most drum trigger pads use a piezo sensor which outputs a voltage pulse when the pad is struck. Piezos are cheap, you can find them in Radio Shack Piezo buzzers or buy them from Digikey (www.digikey.com) for a couple of bucks. I found some in old scrap electronic devices (like smoke alarms) where they are used as speakers or buzzers. I've found the best ones are fairly large - 35mm. They are more sensitive and have higher output.
I experimented with a few ideas and finally settled on using a cake pan as the basis of the pad. The ones I use are 8 inch "Bakers Secret" brand and they cost about $5 for two. They are fairly heavy steel with a teflon coating.
Solder some fine wires to the piezo - one to the brass or metal outside part and one (carefully !) to the thin metallized layer over the piezo crystal. Hot glue the assembly metal side down into the bottom of the pan. You'll have to scrape away any teflon coating in the pan or it won't stick. Tip - put a dab of glue in the pan, and then set it on a hot clothes iron held upside down in a vice. This will keep the glue melted so you can shove the piezo down into it. Work it around (wear a glove so you don't burn your finger) until it is in very close contact with the pan. This is important to getting a good signal whan the pad is struck. Don't overheat the piezo or you may damage it. And don't gob hot glue over the top side of the piezo or it will screw up it's response.
Drill a hole in the side of the pan and mount an RCA jack in it. Solder the piezo wires to the jack with the piezo metal side to ground. The piezo pulse is A.C. but the initial pad hit has positive polarity if you wire it like this. This polarity works best with my trigger to midi unit.
Cut a piece of rubber mouse pad and glue it on top. You will have to experiment to find a mouse pad that has a good "feel" to it when you play it. The ones I used are about 1/4 inch thick. Again, scrape any teflon coating off or the mousepad won't stick. Mine worked best by gluing it around the edge and leaving the center free - probably because it lets the pan bottom vibrate more easily.
Thats about it ! You just have to come up with a way to mount your pads now. Take a look at my cheapo PVC rack to see how I did it.
You will probably want bass drum and hi hat pedals. You can modify real drum hardware or make your own. My pedals are based on a design I saw at Edrum For Free.