[sdiy] MIDI input-selector

[Hallvard Tangeraas]

If my existing projects weren't enough I have plans for yet another one ;-)

It's a combined MIDI input-selector and two separate MIDI THRU devices 
in a single 19" 1U rack enclosure.
Here's an illustration I've made:
http://img179.imageshack.us/img179/88/midiinputselectorx16gp9.png

The MIDI THRU circuits speak for themselves. They allow for two separate 
MIDI INs to be split into 8 connectors each. Useful when I'm running out 
of MIDI OUTs from my Roland A-880 MIDI patchbay and I don't want delays 
and other problems caused by daisy-chaining (IN/THRU-IN/THRU etc.) via 
other modules.
I've already built those boards, having bought the PCBs through Maplin 
and instructions in one of their magazines. I uploaded all of that 
several years ago to here:
http://www.wiseguysynth.com/larry/schematics/thru.htm)

The MIDI input-selector circuit is a completely separate device.
I often find myself having to dump sysex data between a certain synth 
and my computer, and I don't have enough connections available from the 
Roland A-880 MIDI patchbay for that.
So instead of having to disconnect MIDI wires each time I thought an 
input selector might come in handy. I've actually built a smaller one 
using a 4 way rotary switch. Very handy!
This time I want to make it a little more advanced and I was wondering 
if someone has a schematic for this:

- I'm aiming for 16 inputs as the width of the 19" rack enclosure should 
allow for that
- Each input will have its own push-button switch
- I'd prefer that the device "remembers" which input was last selected, 
so that when I turn off its power, then on again the next day it'll stay 
at that same input
- Each input will have an LED which indicates that it's input is selected
- Indication of MIDI activity would also be very handy, so I could see 
that MIDI data is actually flowing through the input. I'm not sure what 
would be most useful here:
      -A) a single LED for each input (as in my illustration) which 
lights up constantly when selected, but flashes when MIDI data passes 
through its input (when selected)
      -B) a single two-coloured LED for each input which lights up 
constantly in one colour when selected, but flashes in the other colour 
when MIDI data passes through its input (when selected)
      -C) Two LEDs. One LED which lights up constantly when selected, 
the other LED flashes when MIDI data passes through its input, 
regardless of being selected or not. This method would be useful if 
you're not entirely sure which input a said synth is connected to, so 
instead of trial and error you'll see where data flows through when 
sysex data is sent from it, which tells you which input to select.


Hallvard Tangeraas