Musical equipment can be expensive. I hate to feel guilty about my own hobbies, so I try to save money where I can. With music, that means a lot of time on craigslist and in thrift stores. I found this sustain pedal for piano keyboard at a thrift store for $5. Not bad! Of course I bought it on the spot, not knowing whether it was compatible with my keyboards at home… it wasn’t. Keyboard pedals come in two varieties: normally open (NO), and normally closed(NC). There’s pretty much no circuitry in the pedal itself. It’s one giant switch hooked up to a 1/4" mono cable. At the other end of the cable, in the keyboard, is whatever circuitry, encoding, or processing is needed. What this means in practical terms is that you can’t simply switch some wires around in a pedal to make it compatible.

Here’s what the actual internal switch looks like. The part you step on presses against the white spacer, which causes the copper leaves to separate…

Which looks like this. A pretty simple mechanism. This is what is meant by “normally closed.” The two terminals on the switch are normally connected, and the connection is broken when the player presses on the pedal. In order for a pedal to work with my keyboard, the opposite should be true. The terminals should be disconnected, and pressing the pedal should make a connection.

Ideally, I wanted to keep the original functionality, and add a switch to swap between NC and NO. That meant not destroying the original contacts. I decided to create a third terminal for the switch. I wanted to create another contact that would hover just below the moving component. So, I dug around in my spare parts and found some old printer parts. Just a mounting bracket and a spring.

This is the basic design. Using a spring was not absolutely necessary, but I thought it would add longevity to the part. I didn’t want the original leaf to have added pressure. To make this mechanism more reliable I added a lot of copper tape and unseemly blobs of solder. Testing this by hand with a multimeter, everything seemed to work. The buzzer on my meter went off as expected. I drilled a hole for the toggle between NO/NC in the side of the housing, and hoped it would work assembled. I couldn’t be sure of the amount of travel until putting it all together.

The final product. It might look a little hacked together, but it has turned out to work reliably so far. The pedal kicks in when you expect it to, and there’s no difference in feel from before the modification. This was an interesting project. I wouldn’t really think of an internal switch as something that could be made by hand without machining. But in this case, especially thanks to the generous space in the interior, everything worked out. I do feel that the normal approach to this project would be to replace the internal switch completely. It was nice to come up with a free solution.