[sdiy] midi clock

[Tim Stinchcombe]

Hi All,

>     This is something I just drew up.  I would want to run it 
> through a logic simulator (Logic simulators are for Wimps and 
> Bedwetters, but it does save time) before I would call it 
> complete.  It turned out a lot more complicated than it 
> sounded.  A Pic or AVR solution would probably be better.
> 
> http://www.silcom.com/~patchell/synthmodulesII/200-1028.pdf
> 
>     Anyway, the clock goes into the phone jack.  A toggle 
> switch selects the edge polarity.  The midi event will be 
> transmitted either on the positive or negative edge....a PLD 
> solution would be a little tidier as well probably...

	Shudder! Because of all this talk of PICs and PLDs and things I
had only been following this thread somewhat half-heartedly, but then I
remembered I had a small book entitled 'Practical Electronic Music
Projects' by R.A.Penfold (Babani, 1994). In it there are several simple
MIDI circuits, one of which is for a control pedal, and another for
detecting any given MIDI byte. Both use a UART chip (6402) which seems
to simplify things considerably. In the pedal circuit the appropriate
bytes are generated using '245 octal transceiver chips, tri-stating 3
bytes in turn to the 6402 - re-jigging the whole thing to output the
appropriate clock byte values, and adding in some sort of variable speed
clock looks more than do-able (and even start/stop messages doesn't look
so bad either). Outputting a pulse to drive an analogue sequencer should
be no big deal, and then adding in a modified version of the
byte-detecting circuit should give a means of syncing in the other
direction too. Just a thought that, to me at least, there does appear to
be an alternative to the PIC/PLD route (in fact I think I might just add
it to my list of projects!). But then of course I might be completely
missing the point somewhere, so somebody please put me right if I am!

Tim
__________________________________________________________
Tim Stinchcombe 

Cheltenham, Glos, UK
email: tim101 at tstinchcombe.freeserve.co.uk