[LAU] Open Source MIDI control surface

Folderol folderol at ukfsn.org
Mon Dec 1 19:10:21 EST 2008

On Tue, 2 Dec 2008 00:38:14 +0100
Nick Copeland <nickycopeland at hotmail.com> wrote:

> > For regular 7-bit stuff, I'll be using a 16-input, 8-bit ADC.  However, 
> > in order to get higher resolutions for the 2 x 7-bit messages, I am 
> > dropping analogue input in favour of rotary encoders.
> Nice. Are they optical? Suppose they must be. The Moog Source used optical rotary pots yonks ago to overcome numerous issues. What is their resolution? I always thought they were quite coarse since the optics has a limit on the width of the shadow being cast but that depends on how the comb wheel is etched and how the leds are aligned, admittedly you do have the benefit that you can just spin the dial to get higher resolution since they don't have a start or end point. You may still get noise depending on the scanning rate and line width - if the scanning rate is too slow you can get spurious direction changes since you only have a 2 bit grey coding. I would be very interested to hear your results, they are cool pieces of hardware.
> Regards, nick.

Grey code encoders are expensive for what they are. If you use an
incremental encoder, resolutions go up to 5000 pulses per revolution.

If you only want relative change and direction just use A & B

In one direction A comes before B, and vice-versa.

If you need absolute position, you get the index reference (designated N
or Z) once every revolution. If you intend to use less than one
revolution just make sure the index pulse is right in the middle of
the most used range and have your software reset the value each time
it's seen.

Will J Godfrey

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