Progress has been made during the weekend
Here we are, an introduction to the disassembled Behringer UMX Keyboard Controller:
At first glance, one can say that the PCB is of very good quality (impressed!)
It has 9VDC Input but it can also be powered from 3x AA batteries (4.5V) as well as USB (5V). I saw a 7805 regulator on it, so I guess if it handles 9V without a heatsing, the 7.5V my PSU pushes out will be just fine.
I’m not going to rewire the footswitch jack to the back panel, since I think a sustain pedal is overkill for a monosynth (and I wouldn’t use a footswitch for anything else).
The power switch is going to be always to the “ON” position (I’ll just switch the AC input and the PSU will power both the controller and the Shruthi at the same time).
I’m going to solder 3 wires from the MIDI OUT to the white connector from the PCB in the picture in my previous post (above) which is going to be the MIDI OUT of the keyboard, which eventually is routed to the Shruthi MIDI IN.
All these white headers are connections for the keyboard and some other peripheral PCBs which have sliders, pots, switches etc. These HAVE to be connected, otherwise the unconnected/floating shift register pins are going to pick up noise and we’ll have lots of random values transmitted over the CC# they control, which may or may not mess with the patches, but are going to create a lot of excess MIDI data traffic, anyway, which is never a good thing. I could try disabling them by the controller settings, I guess, but I’m afraid of a random memory loss/factory reset. I could also make a small pcb which shorts the inputs to the ground, but that would be time-consuming for no particular reason. I think just connecting them and let the rest on the bottom of the case is the easiest/best solution. Moving on…
2) Pitch and Mod Wheels (unpainted yet):
Not much to say here, just two pieces of plastic, pitch has a spring for resetting to the center position. They are connected to two pots, which are on tiny PCBs with 3 pin connectors on them. The cables are removable/replaceable! Behringer has gone out of their way to build an easy-to-service product! They could just solder the wires, but NO! They used connectors instead! Way to go, Behringer!
3) “Pots and switches” board (that’s how I named it, anyway!)
A typical “pots and switches” PCB which is just going to be connected and put under the keyboard (for reasons I have already explained).
4) Control board (again, loosely named)
This is the board that has a slider which by default sends CC#07 messages and controls MIDI volume, it has a set of octave /- buttons along with their LED indications and two other buttons for configuring the controller and assigning controls to various pots and switches for the previously presented PCB. I only want to use the octave/- buttons with their respective LEDs, so what I did is I desoldered the two switches and two LEDs and I made a small veroboard where I put them and soldered a 7-wire ribbon cable to the original board. This way I can save space on the panel surface where the Pitch/Mod Wheels reside and only have the veroboard above with the octave up/dn buttons and the LEDs. The rest of the board is going to be inaccessible at the bottom (volume slider maxed, of course :P)
5) The Keyboard
This thing is of the highest quality! I can’t believe they actually have a small weight inside each key, spring action, and a full metal underside! I always thought the feeling is nice on these keyboards (for their money), but seeing how they achieved it is a whole other matter! I had a small adventure, too when cutting the keyboard down to 3 octaves:
The first part of the adventure is that the last C note (C6) would have to move from the end of the keyboard and replace the C4 (i used the first 3 octaves because the connectors to the motherboard are near the first key).
This is not easily done because all white keys are different! the C4 has a small reccess for the C#4 to snug in. It would look ugly if the keyboard ended that way, so I needed to mod/cut stuff on the underside of the keyboard (where the keys mount) to make the C6 fit in there.
The second part (far worse, btw) is that the controller reads keys in groups of 8 (they are multiplexed). When I cut the board, I was forced to scrape it to reveal the copper tracks and solder a wire on it to close the circuit (otherwise the last 5 keys wouldn’t work because they belong in the next group of 8, for which the circuit closes and backtracks after the place where the PCB had to be cut). This took a good 2 hours to figure out and achieve, but it is done now! Pretty happy with the result!
I think that’s it for now!