Here's what we'll need:
- (Real) Bass drum pedal
- an audio cord with a mono 1/8" plug
- a reed switch/relay
- small magnet(s)
There are quite a few projects like this around the web, but I wanted to capture what worked well for me.
Step 1: Buying a Decent Pedal
I stalked the auctions for a couple weeks and got this barely used Mapex pedal for about $35 (it retails for over twice that).
I definitely recommend a pedal that has floor spurs (if you play Rock Band on carpet), since this pedal won't connect to your plastic set like the original.
Step 2: Planning the Trigger
I decided it was much simpler all around to mount the trigger under the pedal (similar to the Rock Band design).
Step 3: Preparing the Trigger
A (normally open) reed switch is a component which completes a circuit when a magnetic field is applied. These are extremely simple components to wire up and long lasting since a significant physical force is not applied to operate the switch.
To make the trigger for Rock Band I made a run to Radio Shack (choosing convenience over price) and got a 6 foot audio cord with a mono 1/8" plug on one end, a reed relay (the 5V type), and a couple packs of their 3/16" rare earth magnets. The cable was prefect for the job since the other end is already stripped and the wires are tinned and ready for soldering. it would only take a few minutes to prep a cord with plugs on both ends in case you don't find this exact one. Just make sure you have a cord with a MONO plug (with one black line).
Solder the cord to the two leads at the ends of the reed switch. If you get a reed relay, like what they have at Radio Shack, there will be two extra leads you can ignore. After soldering, I encased the whole switch in some heat shrink tubing.
Step 4: Mounting the Trigger
With my particular pedal, placing the switch on the drum clamp worked out best. I just used some electrical tape to hold the switch and a couple zip ties to secure the cable. The magnets sit right on the underside of the pedal on a bracket that holds the chain and they are strong enough that they don't move around without gluing them down.
One thing nice about these small magnets is that you can stack 2, 3, or 4 of them to tweak their distance from the switch and the strength of their field. I got good results with a stack of 3 magnets - with the pedal fully depressed they are about 4-5 mm away from the switch. As far as the alignment of the magnets, you'll probably find you get the best results when they line up with either end of the switch's tube. As I was experimenting with alignment and number of magnets, I made a little LED circuit using the pedal as a switch. You could just probably use the freestyle mode of the game to do the same.
One last step was applying a small felt pad to the top of the drum clamp key. Since I don't have a surface for the beater to hit, the pedal would crash all the way down to the clamp. I also removed the beater since it was causing some extra bouncing (again since there was no hard surface to stop it).
The finished product works great and was much cheaper than converted pedals you can buy online.