[sdiy] uPs kicking my tush

[Tim Ressel]

Yo,

You ever have one of those projects that makes you
think about joining a monastary? Well, I have two of
them. 

First, my Midi-2-CV is STILL giving me headaches. I
finally got the note-ons and offs to work correctly,
but I still have a delay problem where the notes are
sometimes still slewing when the trigger happens.

Second, I slapped together this little USB-CV module
using a DLP Designs board for the USB side of things.
That board came together real easy. Perhaps too easy.
After a day of software sync problems it was playing
notes from a VB program. About 100 or so notes. Then
it would freeze up. A week of ignoring it (except for
the occasional dirty look as I passed by) didn't fix
it. But then I noticed it would lock up when I turned
off the window fan. Eureka! EMI problems! I also
noticed it would lock up when I touched the front
panel. So I grounded the front panel (I thought it was
grounded through the USB board ... wrong), and put a
small cap across the read line to ground. That made it
work on the bench. Ran all night. Yay. So I put it in
the cabinet. It died again. Sigh.

So here's the plan: The Midi2CV is more important, so
I'll tackle it first. I am going to rip out the
single-DAC-8-channel-muliplexed hardware. It gets
buried at midnight in an unmarked grave. I used a
TLV5614 quad serial DAC in the USB2CV project. It was
very easy to hook up to the SPI of the HC11. In fact,
that part worked the first time! So I'll put two of
those in the Midi2CV. No more S/H settling times, no
more scanning interrupts, no more high aspirin bills.

As far as the USB-CV module goes, I'll see if another
week of dirty looks will fix it. If not, I'll put it
back on the bench and test it some more. It will be
cool when its working. There were some issues with it
not being fast enough, but I suspect its my computer
and not the USB causing it. I have a slow machine with
too little memory and windoz '98. USB was an
afterthought on '98. 

Remember those 'March of Time' newsreels?

--tr

PS: Come to think of it, does anybody want the old
analog board?  


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