How make a jammer... (an old posting)

Just fold it over

How to make a “ZipEx” style jammer*

Riddle: How do you make a 4-row hexagonal-key instrument from a 2-row piano-key one? 
Answer: you fold it over and replace the keys!

Background:

Update: I've since made a second generation version, the ZipEx Mark II, the basics are still the same. This rebuild-from-the-PC-board-up way was much harder but resulted in a smaller, wearable version. The Mark II is heavier, but much easier to build. Ken.

A typical electronic keyboard has 2 parts, one is the music control thingy, I’ll call it the controller, and the second the key holder assembly itself.

I have examined just 2 keyboards, A Yamaha DjX, and a Technics P50, but I suspect most are pretty similar.

The key board electronics is on two loooong printed

DjX keyboard PC boards extracted

circuit boards (PCB) clamped into the key assembly. The two boards are connected to each other by a single 6-inch, 12-lead wire, and one of the boards in turn connected by a 10 inch or so, 6-lead connector to the controller.

Each long PCB has clamped onto it a bunch of rubber buttons which make a little dome about 2-3 mm over the PCB. These buttons are depressed when the plastic keys of the keyboard assembly are depressed (I'm not sure what makes them happy).

The underside of the little dome buttons, the part clamped to the PCB, has a little bit of conductive black graphite paint on it, and when it hits the PCB, it closes a circuit, and the circuit generates a signal that the controller interprets.

DjX Keyboard PC board

On the Technics keyboard, each key has two buttons it depresses, presumably at slightly different times to denote a key's velocity.  The Yamaha has a double contact set within each button and the contacts are of slightly different length, thus also hinting at the key's velocity. The important thing here is that you don't need to know further detail on how it works, or electronics.

In my design, I used just the pc boards and the rubber buttons, and rebuilt the key holder assembly.

List of materials

• A keyboard to cannibalize - I used a second-hand Yamaha DjX,  $60
  
• Clear plastic about 3 mm thick for the base – I used a piece from a vinyl window. One should be able to get this from a glass window shop.
• 70 plastic or metal posts – allow extra 10 for wastage - a set of 19 mm nylon spacers for PCB boards worked well here. 
• Material to make 70 plastic or wooden keys. I used Douglas fir for Practice, and settled on Maple rather than Oak
• 35 springs – I cut them in half, as they were expensive, @ 80 cents each. Drop a comment if you need a supplier.  
• 70 key caps.  – made from thick plastic sheets – I have some extras I can send to you. 
• The keys caps were attached to the key-tops with double–sided tape.
• Lots of bolts to attach the posts to the base and to cap the posts
• A tap to thread the posts so the bolts could screw onto them.

Tools

• Drill press with depth control
• 

  ZipEx Half Built
  Drill bits in 1/64" gradations
• Sander is handy
• A protractor, ruler and a compass.
• Several colors of fine-tipped Felt pens to mark up the plastic
• Table Saw to make the keys
  

Software

• Needed is some way to remap the keys to different notes. I used MAX/MAP, an expensive program @ $500 (I have other uses in mind for it, so felt it's price justified). One might be able to use Java, or in a pinch, I can compile my Max version and send you a runtime.  

Layout – the pattern is drawn on the [plastic with fine-tipped felt marker pens.
The spacing between key is determined by the average inter-key spacing of the switches on the PCB, and simple geometry.

The key spacing on the PCB is slightly irregular, due to the irregular placement of black keys. This made things a bit complicated, as the buttons didn't line up with the jammer keys.

ZipEx key

.

There are two ways discovered thus far to mount the circular or hexagonal keys for the jammer:

• mount them on posts - this is fairly fiddly, as 60 sets of holes have to be drilled, and each set is of 8 or so individual holes in addition to making the keys themselves. There were also problems removing friction.
  
• Mount them on little arms - I have not tried this way, but will use this for my mark II version. 
  

Update: Johannes Drinda asked how I made the keys.

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ZipEx Finished

Here's the end product. In addition, the pitch-bend wheel was mounted in the corner and a brass rod attached. 

The black keys at the sides (one PCB was 6 notes longer than the other, so there was overhang) are octave-shifting function keys, used to make it pretend to have more rows and keys. In effect I have a 96-key keyboard that pretends, when needed, to be two keyboards, one for each hand. The blue-black keys in the center divide the two sides of the instrument, and are dynamically assigned to whichever hand is playing near them.

With the special function keys, it's surprisingly easy to play in pretty much any key.

The case was easily made out of brass angle-iron and the leather strap bought at a guitar shop.