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| Top view of the UM44 MIDI Channel Changer |
Like most of my projects, this has been made to solve a problem. My studio's MIDI instruments are on one MIDI buss which is made possible by my UM43 8 channel MIDI merger (Link to come). This makes it possible for me to control any synthesizer from any keyboard as long as I can change the MIDI transmit channel separately from that synthesizers MIDI receive channel. This is often not the case or not easy to do.
The UM44 MIDI Channel Changer came from an earlier and more complex design, the MIDI Warper. This unit took MIDI input data and allowed the user to change the destination MIDI channel for note data, modulation wheel, pitch bender, Sustain pedal and expression pedal. This was connected to the Solaris as changing these parameters on the Solaris was not easy to access.
Although the design of the MIDI Warper allowed for several MIDI controllers channel to be changed, it became over complex for its use. I never changed any of those controllers and only changed the channel.
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| Rear view |
The UM44 is much simpler. It only changes the MIDI channel of all incoming MIDI data. Instead of having a complex rotary encoder and LCD, it has 16 buttons with associated LED. Quick and easy to use.
The hardware of the MIDI Changer is simple from my perspective. It has a Arduino Pro Mini as the MCU connected to a MIDI interface. Unlike the MIDI Warper which has a LiPo battery and all associated charging and step converters, this is powered externally via a USB-B connector. There are two PCBs in this design. One contains most of the electronics and the other the buttons and LEDs.
A slightly more complex part is the reading of the buttons which is done with a slightly dodgy approach of a large resistor ladder read in via an analogue input. When you press a button it picks off the voltage across the large arrange of resistors across the buttons. If you press more than one button at a time you get a false reading. This seemed a reasonable approach given any other approach using a analogue or digital multiplexor would have made it overly complicated.
The LEDs are controlled in a matrix fashion with a 74HC595 8 bit shift register. 4 bits of the 595 control the cathodes of the 4 columns and the other 4 bits control the anodes on the rows.
The case is made from offcuts of stuff I had laying around. I used two pieces of jarrah hardwood to make the majority of the case. The lid and base are 3mm acrylic along with the rear piece. Yet again playing with design to make the case easier to cut and piece together. All routed with my CNC router.
I have made two of these so far. One for the Solaris and the other for my new Tau Hydrae mono synth.