Sunday, November 22, 2015

Boss DR-110 MIDI Sync Project

**EDIT 01/20/2016 - Well. While it works there is an issue that shows up after 5 minutes. The timing goes crazy. When I turn it off a while, it works again. But after 5 minues problems show up again. I wonder if my shrink tubing insulation on the Arduino is causing heat build-up inside there. I am tempted to re-locate the added circuits to the battery compartment and remove the insulation.**

These past two weeks I have been developing and building a MIDI sync input for the Boss DR-110 drum machine.  This allows my DAW to control pattern Start/Stop and to synchronize the clock timing during recording and playback.

I selected the Arduino Micro to process the MIDI data for its tiny size.  It is relatively affordable and can handle incoming MIDI serial data.
While the Micro was on Order from Mouser, I did initial testing with the Arduino Mega.
I accidentally burned the START/STOP traces, so I had to jumper them.  The wires carry the signal pulse to Start and Stop the drum machine.
I removed the clock wire between the CPU board and the Voice board so that I could add a switch.
The switch can choose internal normal clock, or to use the MIDI sync.
MIDI isolation is critical as host/slave devices can have floating grounds at different potentials.
Close up of the MIDI isolation circuit.
My MIDI isolation circuit comes from a design I did on another project.  This is a MIDI shield I made for Arduino Mega, and proved useful for initial testing on this project.
Close up of the MIDI isolation circuit.
The new MIDI isolation circuit.  It would be powered by the Arduino Micro.
I performed testing at every stage, to ensure I was moving forward and solving problems one at a time.
One of the problems was the Micro needed 9v power, and the DR-110 uses 6v by floating the ground to a different potential.  My solution was to DC bias the 3 control signals CLOCK, START, and STOP using a simple voltage divider and tantalum coupling capacitors.  This way the control signals stay above 0v with relation to the ground that the DR-110 uses.
Final assembly.  The added circuits would be tightly squeezed in together with components and needed insulation.
One final test before everything goes together.  The blue light is the Arduino Micro.
Very careful alterations were made for the switch and MIDI jack.
Finished product.

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