Polysix - Mounting the Arduino

While I was pretty excited to jump straight to the end of my story to show a working demo of my aftertouch and portamento, there was actually quite a lot of work that had to get done to get to that demo.  That's why I'm now going back and hitting some of the details, like my last post on how I re-purposed the Arp controls for controlling the aftertouch vibrato.  In this new post, I'm going to talk about how I went about physically mounting my Arduino -- the brain for the aftertouch and portamento -- into my Polysix.  So that you can see where I'm headed, below is the final picture of it mounted inside my Polysix.

My Arduino Mega (in Blue) Mounted Next to the Power Supply

Compared to my Mono/Poly, the Polysix has far less space inside for adding stuff, and the Arduino Mega is not a small board to try to squeeze in.  Luckily, there is a nice open space on the sheet metal control panel, on the vertical part right next to the power supply PCB (see pic below).  It seems just right for the shape of the Arduino Mega.  But how will I actually attach it?

Well, because the Arduino Mega already has some mounting holes in it, I could just use screws.  But, to prevent pressing the backside of the Arduino against the electrically-conductive sheet metal, I need some standoffs.  Since most standoffs are threaded on both ends, the plan is to drill some small holes in the Polysix's sheet metal, mount the standoffs via screws through those holes, and then to use more screws to attach the Arduino to the standoffs.  Even for me -- the mechanically dis-inclined -- this seems feasible.

That Empty Spot is Where I'll Put the Arduino.  One Standoff is Already Mounted.

The first step was for me to find some standoffs.  For no particular reason (other than that they were easy for me to get), I got some #4-40 threaded aluminum standoffs (see below).  Plastic ones would probably work fine, too.  I think that I got standoffs that are 1/2" long, but they might have been a little shorter.  I also got a bunch of really short #4-40 screws and a few washers.  My screws were regular silver/gray color, which means that you can easily see the screw heads on the outside of the synth.  If I did it again, I'd try to find black screws so that they'd blend in better.

Threaded Aluminum Standoffs For Mounting the Arduino to the Inside of the Polysix.

With the standoffs in-hand, I then proceeded to drill the holes in the Polysix's sheet metal enclosure.  Drilling into sheet metal is not something that I wasn't familiar with, so I asked around at my work place.  Apparently, my regular (ie, cheap) drill bits can cut into sheet metal just fine.  Cool!  The only trick is that the drill bits have a hard time getting started on sheet metal.  Until they can bite in, they tend to wander around the surface of the metal, which makes it hard to get the hole where you want it.  So, according to one of helpful co-workers, I should use a punch-thingy to put a small indentation in the surface of the metal, which allows the drill bit to bite more easily.  The punch that I borrowed is shown below.

Spring-Loaded Punch for Making it Easier to Drill into Metal

Once I decided where I wanted a hole (by holding the Arduino up to the metal panel and using a thin pencil stuck through the Arduino's mounting holes to mark the spot on the sheet metal), I grabbed hold of the Polysix's panel, pressed in the punch, and waited for it to "pop!".  When it finally popped, it really startled my wife in the next room.  It's not particularly loud, but it is a bit sharp sounding and totally unlike any other sound that I usually make when futzing with my instruments.  It's good to keep things interesting around here.

Pressing in the Spring-Loaded Punch.

I'd like to now show a picture of the tiny dimple that was made by the punch, but it's really too small for me to take a good picture.  So, you'll just have to imagine a very very small dimple in the surface of the sheet metal.  I couldn't really believe that it was big enough to help the drill bit seat, but it was.  It worked marvelously.

With the dimple to get me started, I used a small drill bit to get my initial hole through the sheel metal.  Since I have old bits that aren't very good, it took me a while to get through.  Once I was through, I stepped up to a bigger bit to enlarge the hole so that my #4 screws would pass through.  

To then mount the standoff, you use one screw (and washer) from the outside of the back of the synth, you pass it through the hole that you just made, and you screw into the female threads in the standoff.  After tightening, the standoff is nicely attached to the synth.  In the picture above, you can see that two standoffs are already in place.

Once all the standoffs are in place (I used three), you can place the Arduino over the standoffs and use more screws to attach the Arduino to the standoffs.  If you're really lucky, you located your standoffs correctly and they line up with the holes in the Arduino.  I was mostly lucky...two holes lined up well and one was a smidgen off.  It was close enough, though, that I could angle the screw a bit and get it to seat sorta good enough.  As usual for me, it's ugly but it works.

Below is another picture of the Arduino fully-mounted inside my Polysix.  Not bad!

The Arduino is Fully-Mounted Inside my Korg Polysix

Now that I'm looking at this picture with fresh eyes, I sure do see a lot of loose wires running round.  In particular, lots of wires are needed in order to connect the Adruino, which is replacing the Key Assigner 8049 microprocessor, to the socket that used to hold the 8049 microprocessor.  The 8049 was located just underneath the keybed, so that's why you see the rainbow of wires passing from the Arduino on the right to the underside of the keybed on the left.  I'd definitely like a better way of handling all this wiring.  As usual, there's always more "cleaning up" that could be done!

Thanks for reading!