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

[Theo]

Your talking LFO so why R2R when you can PWM.
A 8 pin tinyAVR or PIC can do it, a RC filter on the pins used for the PWM
is enough.
Frequency is low, so no need to use the mode PWM of a timer, software will
do.

HTH
Theo


----- Original Message -----
From: Roy J. Tellason <rtellason at blazenet.net>
To: Synth-DIY List <synth-diy at dropmix.xs4all.nl>
Sent: Thursday, October 14, 2004 2:45 AM
Subject: Re: [sdiy] Simple MIDI-syncable LFO...?


On Wednesday 13 October 2004 08:26 pm, Tim Parkhurst wrote:
> > > 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.

> Right, I see what you mean. Well, actually by "four D/As" I meant four R2R
> networks.

For ring counters you don't use R2R networks,  see Lancaster's book for the
details on this.  They're weighted,  yeah,  but not binary weighted.
Another
ring counter,  that happens to have a 2-input gate providing each output,
is
our friend the 4017.  Only one output is active at a time there.

> You could very easily use one counter and then wire up the R2R
> networks so that your outputs were 90° out of phase, but I was thinking of
> using four counters so that you could preset/reset them at different times
> so that you could change the phase 'on the fly.'

Just take your resitor weights from different outputs.  Still only need one
counter.  :-)

> > > 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... :-)

Still!  :-)