Sunday, March 17, 2013

Polysix - Cabling for the New Keybed

Continuing from this post where I began preparing my new Fatar keybed for installation in my Korg Polysix, I've now begun to prepare the cabling from the keybed to the keyscanning electronics.  I got both the keybed and the electronics from and they designed their electronics to utilize a cheap and widely-available cabling systems, which is cool.  The connection for the keyboard, for example, is setup so that one can use that big, wide, flat, ribbon cable that used in older computers to connect a hard drive to the mother board.  The picture below shows what I'm talking about.  What I need to do is modify the cable to connect between the Keyparts electronics and the Fatar keybed.

Raw Piece of Ribbon Cable That Will Be Modified for Use with my Fatar Keybed
One end of this cable (the one shown) can be used without modification to mate to the Keyparts electronics.  Fantastic.  The other end of this cable  needs to be modified.  I need to remove the existing connector (another one of the black things) and add the connectors that'll mate to to the sockets on the bottom of the Fatar keybed.  What do those Fatar connectors look like?  See below.  I'd never seen this kind of connector before.

The Orange Things Are the Connectors on the Bottom of the Fatar Keybed
Luckily, the folks at Keyparts UK have the mating connectors.  When they send you the connectors (two are needed for a 61-key keybed), they also include some guidance on how to put the connector onto the ribbon cable.  That's nice of them.  Unfortunately, their guidance assumes some basic knowledge about this style of connector and I lacked that knowledge.  For anyone experienced with putting connectors on this kind of ribbon cable, you wouldn't have had any problem.  For me, though, I'm only familiar with connectors where the wire must be stripped and soldered and that's clearly NOT how these work.

So, after talking with some of my electronics-knowledgeable co-workers, here's the key bit of information...there is NO stripping and NO just crimp it onto the ribbon cable!

For these Fatar-compatible connectors, here's what you do:

1) Cut the black connector off the 40-conductor ribbon cable
2) Split off a group of 16 wires from the ribbon cable
3) Stick the whole group of 16 into your connector (no stripping!)
4) Squeeze together the connector to crimp it onto your cable

That's it.  You're done.  How easy is that!?!

To flesh this out a bit, here are some know, for the I was a couple days ago...

First, cut off the black connector shown in the first picture above.  Second, split off a group of 16 wires from the 40-conductor flat cable.  Check out the picture below.  You can see that I've broken out one group of 16 wires (top) and already attached the orange connector.  Then, I broke out the second group of 16 wires (middle), which left a group of 8 wires with nothing to do there on the bottom.

Splitting Off Groups of Wires for Attaching the Connectors
Now for the third step...just stick the end of the ribbon cable into the connector (see below).

Just Stick the Unstripped Group of Wires into the Connector
Fourth, get some sort of flat-faced tool and press firmly to crimp the connector closed.  You do have to be a little careful here.  The trick is to find the right tool that'll apply a relatively even force across the width of these're trying to avoid bending or breaking the pins.  My approach was to use a couple of pieces of scrap aluminum to sandwich the connector and spread out the force.  Then, I used a small table-top arbor press (see picture below) to do the squeezing.  This worked like a champ, but is probably overkill.  If I didn't have the arbor press, I think that a set of pliers (plus think strips of plastic or metal to spread the force) would probably work fine, too.

Using an Arbor Press to Apply Even Force to Crimp My Connector

By applying the crimping force, the internal features of the connector bite through the wire's insulation to make the connection.  The internal features permanently deform during the process, which causes the connector to be firmly attached to the end of the flat cable (see below).  It's an absolutely brilliant system.   I can't believe that I'd never seen it before (yeah, I know, welcome to 1981, right?).

Finished Cable with Both Connectors Attached.
So, with the cable finished, it can be mated to the underside of the keybed.  I tested it out by connecting the other end to the Keyparts UK keyboard scanning electronics.  It works!  I can't believe how much easier this ways than stripping and soldering each of these wires.  Wow.  What a great system

The Modified Ribbon Cable Shown Attached to the Bottom of the 61-key Fatar  Keybed

Edit: Here's the next step...all the parts working together

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