[sdiy] 3 bit A to D with hysteresis?

[ChristianH]

Couldn't resist, and did some more thinking...

The difference between input voltage and DAC'd 3 bit output should give
a feedback voltage as well (probably a primitive R network DAC will
suffice). Put that difference into a comparator with 1/2 digit voltage,
and there you have a polarity change right in between the switching
thresholds.
Well, a 1/2 digit voltage comparator isn't that far apart from one more
bit of resolution. But if you want do build a flash ADC this means 7+1
comparators instead of 15.

Christian


On Tue, 24 Oct 2006 17:23:43 +0200 ChristianH <chris at chrismusic.de>
wrote:

> I think you'd need one more bit for that.
> ADC with 4 bits, and positive feedback the inverted LSB,
> use the 3 other bits for output.
> 
> You have 7 switching thresholds for the intended 3 bit data word.
> It will be necessary to increase the ADC input slightly when it's just
> above a threshold (i.e. LSB=0), and decrease it when it's just below, in
> order to prevent stuttering (just likje a normal Schmitt trigger does).
> 
> That's just a rough thought about it. 
> Anyway, gotta get back to my day job now...
> 
> Christian
> 
> 
> On Tue, 24 Oct 2006 16:32:51 +0200 "JH." <jhaible at debitel.net> wrote:
> 
> > Use a 3 Bit DAC and feed back a portion of
> > the encoded + decoded signal to the analog path ?
> > 
> > JH.
> > 
> > 
> > ----- Original Message ----- 
> > From: "Paul Perry" <pfperry at melbpc.org.au>
> > To: <synth-diy at dropmix.xs4all.nl>
> > Sent: Monday, October 23, 2006 4:20 PM
> > Subject: [sdiy] 3 bit A to D with hysteresis?
> > 
> > 
> > Is there an elegant way to make a simple & cheap
> > 3 bit A to D  with hysteresis?
> > I'm hoping to have a footpedal give a control voltage
> > that drives a 3 bit output counter, but wiht hysteresis so 
> > there is no problem of being stuck on the edge &
> > stuttering.
> > Maybe there is an 'obvious' solution applicable to all
> > A to D converters?
> > (yeah, I know...... use a micro...... but before I do....)
> > 
> > paul perry melbourne australia