[sdiy] Polyphonic keyboard scanner

[Bruce Duncan]

I bought that book and found it less than helpful.
It assumes a far greater understanding of the topic than you will 
have as a beginner.
Books never seem to be much good for this kind of thing as they 
always seem to be focused on quantity of information over clarity.
Also they are out of date by the time they are published.

There are simple examples available from Microchips web site and all 
you really need to get going
is a template for your chosen processor and the family reference manual.
Download the latest MPLAB software and purchase an ICD2 clone from 
Sparkfun or similar.
Or better yet get the real thing from MCHP. You won't regret it later on.
Then just start working through basic pin toggling and simple logic 
experiments till you get the hang
of Assembly and instruction set. The Piclist 
http://www.piclist.com/techref/piclist/index.htm
has tons of examples for earlier 16 and 18 series devices and is a 
treasure trove of clever
methods to debounce switches and perform math without hardware multipliers.
Take a look at some of Tom Wiltshires PIC projects. First rate synth 
related stuff for 8 bit PICs.
You will get a good feel for setting configuration bits and assembly 
program flow from looking at these examples.

Once you feel comfortable with the basics get some 16bit dsPIC30F 
samples and then you will be cooking
as they have better facility for math, better ADCs, more RAM and 
faster clock speeds. Also the instruction set
is far more efficient IMHO and easier to use. The 33F series are 
super cool but a major step up
in complexity and non-C language examples are hard to find. Most of 
what applies on the 30F series does apply to the 33F though.
The 32bit PICs are a totally different beast and so far seem 
unsuitable for synth use. Too early to say.
It is a terrific learning experience once you get going although it 
can be a bit of a struggle at first.
You will be amazed at what is possible though and it will consume you 
entirely for weeks at a time if you let it.
I don't consider myself to be a programming expert by any stretch but 
I know a hell of a lot more than I did when I started
and with the continued improvements in microcontrollers and 
availability it is difficult to ignore the benefits they offer
in synth related design. Analogue or otherwise..

Bruce


>Thanks to all for the replies.  I am very interested in looking at the
>Oberheim OB-Xa schematic.  Any hints where I might find it?
>
>Also, I bit the bullet and bought a book on microcontrollers today (at the
>brilliant Powell's Technical Bookstore in downtown Portland, OR -- if you've
>never been, and you find yourself in the area, you really must check it
>out!).  The book is "Programming and Customizing PICmicro Microcontrollers"
>by Myke Predko.  It's nearly 1200 pages, and it came with a PCB in an
>envelope behind the front cover for building a PIC programmer (how cool is
>that?!? -- I've never bought a book with a PCB in it before!).  Get this: it
>was only $22!  And, the project on page 922 is a switch matrix key
>interface!
>
> > I cloned and upgraded the Tim Orr ETI Polysynth's polyphonic controller.
> >
> >  > http://rubidium.dyndns.org/cag/pdf/etipoly.pdf
> >
> > There are some mistakes in the poly assigner schematic. I have all the
> > errors noted down somewhere - as well as a detailed section by section
> > break down of what is actually going on. I may try and dig it out if I
> > can find it.
> >
> > Other things to note: Cyclic assignment, like the OB-Xa, with optional
> > note stealing and switchable total voice number, 1, 2, 4 or 8. Unusual
> > +/-5V buss bar on the keyboard. Linear glide with OTA control.
>
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