[sdiy] Simple MIDI-syncable LFO...?

[Roy J. Tellason]

On Wednesday 13 October 2004 05:50 pm, Tim Parkhurst wrote:

> This link shows a guitar effects page that describes a similar 'digital
> LFO' made from ring counters. This makes getting a triangle wave very
> simple, although the saw wave goes away. Still, this might be the way to
> go, or at least some good inspiration.
>
> http://www.geofex.com/Article_Folders/LFOs/psuedorandom.htm
>
> Any comments?

That page is silly.  "No permission for local copies"?  How the heck does he 
think a browser renders something,   from _his_ copy over the 'net?  I guess 
I better flush my cache to be sure...

> Anyone out there built something like this? I think this might be a neat way
> to do a quadrature LFO too (one clock, four counters & four D/As, pretty
> cheap and easy).

You're missing it.  You don't need D/As,  that's what those resistor networks 
are for.  You also don't need four counters,  just four resistor networks.  
Keep the impedance high enough and they won't interact with each other.  Or 
use some gates/buffers to isolate them,  lots simpler than duplicating all 
that other stuff.  Don Lancaster touched on some of this in his CMOS 
Cookbook,  and appears to have a bunch of related material on his web site as 
well.

> With a little fiddling, you could make the phase between the outputs
> adjustable (albeit in resolution-limited steps, but still might be fun).
>
> Whadaya all think?

I think you can do quite a lot with a mess of resistors...		:-)