Related to MAKE 04, Circuit Bending

Circuit-Bending: External Controllers

by Sabastian Boaz, Cristiana Yambo
October 24, 2005

This article continues the Circuit Bending project from Make 04. You can enhance your bent Casio SK5 Keyboard with external controllers based on Ethernet cables that let you plug in, turn on, and rock out!

1. Add external controller port.

The external controller is one of the more innovative features of this project. It's an ordinary Ethernet jack that's wired to a set of notes (or drum sounds) on the keyboard, rather than to a network. With the jack in place, you can plug in and trigger notes from your own controller devices.

1a. Locate keyboard and drum pad connections. The keys are attached to an auxiliary PC board, which feeds the main board via a ribbon cable. Lift the membranes that the keys press against. For each key, you'll see a round contact area with two connections. Follow one of these traces out to the ribbon. Each key completes a connection between a different pair of wires in the ribbon.

Find the contact area.

Follow the trace out to the ribbon.

1b. Test connections. To test what notes can be triggered by the external controller, switch the keyboard on and then manually jump pairs of contact points on the traces that lead to the ribbon cable. If you hear a sound, then you have triggered a key. Write down that connection and test another pair. The connections follow a pattern, so after a few tests you can try to guess what all the connections will be.

Test pairs of contact points.

1c. Solder connections to port. Once you've found enough connections, decide which eight contacts you want to connect to the port. Solder eight wires from these contacts to each of the pins on the Ethernet port.

External controller port with connections.

1d. Secure port to case. Cut a hole in the keyboard case and mount the Ethernet port in the hole.

Port glued into place on side of case.

2. Build external controllers.

Now that the port is wired up, what can you do with it? Here are two external controllers you can build for your Ultimate SK, a Snake Controller and a Key Box Controller.

2a. Snake Controller. This one's very simple to make and fun to use. Cut one end off of an Ethernet cable and strip about ten inches off the outer insulation. Then spread out the wires and strip the insulation off parts of each of them. There's no specific way to do this, so when you're done, it won't look very pretty. Now connect the cable to the port, bend and crush the stripped wire ends together, and you'll generate a steady stream of semi-random sounds.

Separate and strip the wires in the cable.

Finished snake controller.

6b. Key Box Controller. To build this controller, drill a grid of holes in a box. Next, hot glue momentary switches into the holes, with the keys exposed and pressable; we used old keyboard keys and another plastic bead box. Then take half of an Ethernet cable, spread and strip the wires inside, and connect them to the keys in a matrix pattern, so that each key connects a different pair of wires. That way, each key will play a different note or sound. If you're using more than 16 keys, you can splice some of the Ethernet cable wires into two wire connections. Finally, drill a hole in the side, hot glue the Ethernet cable through the hole, and you've got an alternate keyboard.

Finished Key Box Controller.