New question: apparently the iTrack Dock does not recognize the Teensy Midi of Justin Thursday's USB-Boy. It is supposed to accept all class compliant devices and my midi keyboard works fine, but nothing happens with the USB-Boy. The USB-Boy also works fine with my computer, so I know it is fine. Any advice on how I might either fix this or some other workaround?

I also have problems with junk notes and program changes from my arduinoboy (junk note happens once every few minutes and program change more seldom, so this is not a big problem - but still frustrating).
I get these problems on both my Access Virus C and SammichSID synths.
On my Virus C I can work around it by disabling program changes and setting key range (the junk notes are usually very high).
Maybe this is also possible on the Slim Phatty?

Good tip with the Y-command and using a powered MIDI device. I will try with a MIDI merger and see if it works better.

That Y command tip was a good one, Alex, thanks again! It not only keeps the Slim Phatty on the setting it should be but also allows me to switch settings without touching it, which means one less thing I have to keep track of during my live performance. Eventually I'll try a midi Thru to see if it helps with the errant notes, but the result is much more tolerable right now.

Another interesting point, tho, is that the Slim Phatty is the only device affected by the junk Program Changes. The Animoog and Drum Machine never seem to have any troubles.

I mean, my actual solution recently has been just recording the midi into reaper,deleting the program changes, and moving/removing ghost notes by hand.  It's not ideal, but it works.

It depends on your definition of what constitutes a fix. Anyways here is my setup chain

Gameboy _> Midi Solutions Merge -> *Midipal -> Midi Thru x4 -> Gear

* Device is powered and maybe is boosting the midi signal?

Have no idea if this helps the problem or not, but I havent seen the random program change problems.

Ha I see, right.
But it does not really fixes the problem, neither the problem with random notes.
And you have to change every table as well...

The issue is the arduinoboy spitting junk program change events, which cause the settings on the synth to change, it's really frustrating when it happens.

What happened a lot?
I don t understand what problem you are working around...

Thanks guys, I'll give these ideas a try.

This was something that happened a lot when I was doing more gameboy midi stuff, the way that I worked around it was to have the instrument also send a program change command in a table on the instrument. like this :

but replace the Y00 with the relevant program number (in hex).

I guess some arduinoboys are not up to midi spec, so running it though a thru makes the receiving device get a better electrical connection.

Just to be clear, if I run the Midi out to a Thru box before sending it to the devices, it should help keep the signal clean?

Yeah, I've been having a lot of fun with my arduino setup but getting everything to work properly has been a little frustrating. I have DMG > arduino > Slim Phatty > Animoog > Drum Machine via midi thru. The occasional random note is unwelcome but tolerable. The Slim Phatty suddenly changing settings and presets is a bit more of a hindrance.

Some people say the problem is the circuit doesnt have something or other on the arduinoboy output, so you can try connecting through a thru or merge box like I do, but I dont see the dropouts.

Thanks herr_prof. I had a feeling you'd be the one with the answer