Nuts and Volts - January 2016

In addition, there is a small 1/8” ( 3. 2 mm) TRS (tip, ring, and sleeve; sometimes called a ‘stereo jack’) jack next to the MIDI out connector that was intended for future controller expansion. The planned accessory was a dual foot controller that would add a sustain pedal and a volume/foot controller potentiometer pedal. The function of the volume/foot controller is selected from the ‘D-pad’ gaming control on the front panel. The D-pad is the four-position flat joystick control on the front panel which offers switch closures for up, down, left, and right movements.

In summary, Table 1 is a list of the front panel MIDI functions (note some buttons are labeled differently between the Xbox, Sony PlayStation, and Wii versions).

You may want to label these MIDI functions like I did as shown in Figure 2. Since I painted the body of mine, relabeling was needed anyway. If you do plan to paint the body on yours, remove everything from the case. That will make painting much easier, and prevent potential issues with the electronics.

Let’s Add a MIDI Sustain Switch

Now comes the fun part: Tapping those features in the 1/8” pedal jack. I think most will agree that a sustain pedal on a two octave keyboard is not very useful. However, when used on a stage as a keytar, a neck-mounted sustain switch is quite useful for theatrics, and a look at most higher-end keytars reveals this is a fairly common feature. We could add another switch to the neck for this purpose, but there is already a nice momentary switch mounted on the neck in an ideal position. The function of the current switch is not very useful, however. When held down, it causes the ribbon controller — usually controlling modulation — to instead control pitch bending. It’s quite awkward to do pitch bending this way, so I came up with another method.

I added a small SPST toggle switch to an unused area on the front of the body. I then desoldered the wire from the current neck switch (labeled ‘overdrive’ on the neck printed circuit board [PCB]) and soldered it to the toggle switch. I then ran ground to the other terminal of the switch. The ground is conveniently located next to where the overdrive wire was on the neck PCB. Details are shown in Figure 3. When the switch is closed, pitch bend mode is activated on the ribbon controller. An open switch defaults the ribbon to modulation mode.

To convert the existing neck switch into a momentary sustain switch, I ran a wire from the 1/8” TRS pedal jack’s

Post comments on this article and find any associated files and/or downloads at www.nutsvolts.com / index.php?/magazine/article/january2016_KeytarMIDIController.

■ FIGURE 1. Stock Rock Band 3 keyboard.

■ FIGURE 2. Repainted keyboard with MIDI functions labeled.

■ FIGURE 3. Neck PCB. To start the MIDI sustain switch function and move the pitch bend/modulation selection switch, desolder and remove the top wire in the ribbon cable. It's labeled "over_d" on the PCB.

Next, solder a wire on the underside of the "gnd" wire solder connection next to the "overdrive" hole.

Table 1.

MIDI Command PlayStation Wii Xbox MIDI Sequencer Start Start + (plus) Start MIDI Panic (all notes off/reset) All 3 buttons above All 3 buttons above All 3 buttons above Keyboard octave decrease by one (square) 1 X MIDI Program increase by one (triangle) 2 Y