[sdiy] Endless pots?

[karl dalen]

--- Den sön 2010-12-05 skrev Mike Pepper <profpep at hotmail.com>:

> Från: Mike Pepper <profpep at hotmail.com>
> Ämne: Re: [sdiy] Endless pots?
> Till: synth-diy at dropmix.xs4all.nl
> Datum: söndag 5 december 2010 18:39
> I can see a couple of snags in the
> endless pot idea; when the slider hits
> the deadband the output voltage is indeterminate, and as
> the slider crosses
> the deadband, the output jumps from one end of the scale to
> the other,
> depending upon the direction of rotation.

> Basically it's this: you have a knob with a disc of
> polariser film on it's
> shaft. The disc endlessly rotates, when the knob is turned.
> Above the disc,
> set at 90 degree angles, you have two Light Dependent
> Resistors, (LDRs),
> each which has another piece of polariser film over it, the
> films aligning
> to 90 degrees also. Under the disc are two LED's pointing
> at the LDRs. When
> the disc rotates, the effect of the crossing and uncrossing
> of the polariser
> films is to vary the light falling on the cells, in a
> roughly sine/cosine
> fashion. This means the voltages derived from the cells go
> smoothly from min
> to max and down again as the disc rotates, and there is no
> sudden jump at
> the dead-band as there would be with an endless pot.

I had the idea of 360 deg pot cabon/plastic just the regular
P160 model design where at 90deg one had a tap/leg out of 0 ohm
and at 270deg a tap/leg of e.g 10Kohm, and the regular circular
center tap. E.g apply AG at 90deg and +5V DC at 270deg and 
variable DC at center tap. So one gets two sides with equal
value and no jumping and no dead zone but only a variable
range of 180deg. Full rectified sinus pot!

Reg
KD