[sdiy] digital control of CV [rotary encoders]

[Seb Francis]

Tom Wiltshire wrote:
>
> So then I started experimenting with measuring the time between 
> detents, the rotational velocity, and incrementing the count 
> proportionally (as suggested above). This was a disaster. Whilst the 
> count goes up a lot if you turn fast, and slowly if you turn slowly, 
> getting to any particular value is more or less impossible. I found I 
> couldn't control or judge accurately how fast I had to turn to get a 
> given increment. For example, if I want a value of 500, and the 
> current value is 400, I need to turn at a speed that gives me an 
> increment in the tens, say. How fast is that? I had no idea.

Mackie use rotary encoders on their digital mixing desks that implement 
a speed-up algorithm when turned fast.  This actually works very well - 
it's easy to get precise values when turning slowly, and when spun fast 
you can jump through the range very quickly.  It helps a lot that they 
use very easy to spin encoders (i.e. they are optical not mechanical).  
They also have a ring of LEDs around each encoder so you can see the 
approximate position at a glance (and also a software GUI where you can 
see the precise value).

It really is much more satisfactory to use this kind of system compared 
to a sampled pot where you have to move to the right position to pick up 
control, or worse where the control just jumps when you move the pot.

I suspect the main reason why there are not more (good quality) rotary 
encoder implementations is simply cost - they are relatively expensive, 
especially with a ring of LEDs round the outside.

But of course nothing beats a REAL pot directly adjusting a REAL analog 
circuit (IMO!)

Seb