[sdiy] 3/4 bit A/D converter (was: Sample&Hold thoughts)

[Grant Richter]

> I have done a module that consists of a string of 17 equal resistors, giving
> 16 voltage levels. Those are fed into the "-" input of 16 comparators, the
> "+" inputs are all together connected to the input signal.
> All comparator outputs are summed with equal resistors.
> 
> That gives effectively a 4-bit A-->D and then back D-->A conversion. I have
> made the top end and the bottom end of the resistor string CV controllable.
> *very* interesting effects when you put LFO´s in there !
> 
> This makes very strange sounds; depending on which signals you feed
> into it. When putting CV´s through it, it behaves lika sort of a quantizer.
> 
> The 3-bit version does use only 9 resistors(8 levels); here the effect is even
> more pronounced.
> 

If you use LM319 comparators and put RGB video through it, it produces an
effect called "posturization" or fixing of the color levels. This was used
in the Sandin Image Processor. The output summing resistors can be replaced
with pots for variable levels.