Poly keyboard circuits

[gstopp at fibermux.com]

     Do you mean multiple CV outputs, rather than MIDI out?
     
     If so, and you want to copy a commercial circuit, you should probably 
     ask Juergen Haible about his Oberhiem interface circuit clone. It's 
     quite a lot of work, as I understand it. However Juergen is well known 
     for his ambitious (and very impressive) projects!
     
     A poly CV interface is the kind of thing that is almost too complex to 
     do without a microprocessor. It's nice to have several voice 
     assignment algorithms to choose from and this is where software 
     becomes very desireable as the way to implement it. (MIDI-CV 
     conversion is another example of this kind of complexity.) Dedicated 
     microprocessors with code in EPROM are almost always used for these 
     devices.
     
     Here's another possibility - if you have access to cheap (or free) old 
     PC motherboards then you can do this with a minimum of expense and 
     electronics. Find a nice working motherboard, build a multi-channel 
     DAC that fits on the parallel port as output, and build a keyboard 
     scanner that fits on the parallel port as input (it's helpful if you 
     can find a diode-matrix keyboard). Add enough PC hardware to get the 
     system running and write the software in some easy language like 
     QuickBasic or C. You can boot the whole thing off of a floppy if you 
     want. Try to find a machine that has BIOS options so that it will boot 
     without a PC keyboard attached.
     
     What with the advances in PC technology, it's not difficult to find a 
     486/33 motherboard for real cheap, or maybe even *free*. Same with the 
     floppy drives and other pieces. The disadvantages compared with a 
     dedicated microprocessor design are size and power requirements, but 
     the advantages are ease of design, and the fact that you can develop 
     the code on the machine that runs it!
     
     Just some ideas....
     
     - Gene
     gstopp at fibermux.com


______________________________ Reply Separator _________________________________
Subject: Poly keyboard circuits
Author:  "Steve Jones" <sj2393 at ansys.com> at ccrelayout
Date:    4/24/97 5:15 AM


All of the keyboard schematics I've seen at the various 
sites have so far been mono (admittedly, I have probably 
not been thorough enough).  Can anyone recommend a poly 
keyboard circuit?
     
steve