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Rotary voltage selector

2007-02-17 by Andrew

I would like to have a Rotary knob that would select between eight
specific voltages (to come out of the rotary to a jack). The voltages
would *not* have to be exact, maybe like within 0.5 volts (+ or -) of
the intended voltage.

Could I do this by supplying +10v to eight different resistors, and
connecting the other end of each resistor to the eight inputs of the
rotary knob? (and then the output of the rotary to a jack) Assuming
I get the right resistor for each specific voltage I want, would this
work?

I suppose I could use resistor trimmers or even potentiometers instead
of resistors for a more adjustable setup?

thanks :)
Andrew

Re: Rotary voltage selector

2007-02-17 by Laurie Biddulph

If the resistors are connected in series with each being a calculated value
then you will have a series of voltages as required. You will need to be
wary of what you are connecting to as the impedance of that circuit could
well upset the balance of your series divider network and thus change the
values. Use high tolerance resistors to get accurate and stable voltages.

A better approach would be to use an adjustable voltage regulator with a
series of switched resistors (or trimpots) in the ADJ leg of the circuit.
The output will be far more stable and, if trimmers are used, can be easily
adjusted to any range of voltages desired. Have a look at the datasheet for
the LM317L which shows not only switchable output voltages but also
`digitally selected' switchable outputs.

Best Regards

(Mr) Laurie Biddulph
Phone: +61 (0)2 4340 0938
Mobile: 0400 257 645

Elby Designs
ABN: 70 022 727 605
http://www.elby-designs.com

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----- Original Message -----

Show quoted textHide quoted text

From: "Andrew" <dumpstatic@...>
To: <cgs_synth@yahoogroups.com>
Sent: Sunday, February 18, 2007 8:53 AM
Subject: [cgs_synth] Rotary voltage selector

>I would like to have a Rotary knob that would select between eight
> specific voltages (to come out of the rotary to a jack). The voltages
> would *not* have to be exact, maybe like within 0.5 volts (+ or -) of
> the intended voltage.
>
> Could I do this by supplying +10v to eight different resistors, and
> connecting the other end of each resistor to the eight inputs of the
> rotary knob? (and then the output of the rotary to a jack) Assuming
> I get the right resistor for each specific voltage I want, would this
> work?
>
> I suppose I could use resistor trimmers or even potentiometers instead
> of resistors for a more adjustable setup?
>
> thanks :)
> Andrew
>
>
>
> The CGS Modular Synth home page: http://www.cgs.synth.net/
>
> Yahoo! Groups Links
>
>
>
>

Re: Rotary voltage selector

2007-02-18 by Andre Majorel

On 2007-02-18 09:59 +1100, Laurie Biddulph wrote:

Show quoted textHide quoted text

> From: "Andrew" <dumpstatic@...>
>
> > I would like to have a Rotary knob that would select between
> > eight specific voltages (to come out of the rotary to a jack).
> > The voltages would *not* have to be exact, maybe like within
> > 0.5 volts (+ or -) of the intended voltage.
> >
> > Could I do this by supplying +10v to eight different
> > resistors, and connecting the other end of each resistor to
> > the eight inputs of the rotary knob? (and then the output of
> > the rotary to a jack) Assuming I get the right resistor for
> > each specific voltage I want, would this work?
>
> If the resistors are connected in series with each being a
> calculated value then you will have a series of voltages as
> required. You will need to be wary of what you are connecting to
> as the impedance of that circuit could well upset the balance of
> your series divider network and thus change the values. Use high
> tolerance resistors to get accurate and stable voltages.
>
> A better approach would be to use an adjustable voltage
> regulator with a series of switched resistors (or trimpots) in
> the ADJ leg of the circuit. The output will be far more stable
> and, if trimmers are used, can be easily adjusted to any range
> of voltages desired. Have a look at the datasheet for the LM317L
> which shows not only switchable output voltages but also
> `digitally selected' switchable outputs.

Or perhaps more simply just buffer the output of a voltage divider
with an op amp in voltage follower mode ?

V+ ^
|
|

>

R1 <

>

| ___________
+--o | |
| \ | _ |
< \ | | -_ |
R2 > o--+--|- -_ |
< | _>--+--o OUT
| --|+ _-
+--o | |_-
| |
< ===
R3 >
<
|
|
V- v

> > I suppose I could use resistor trimmers or even potentiometers
> > instead of resistors for a more adjustable setup?

Sure but then you would have to do it with 8 separate voltage
dividers instead of a single 8-tap voltage divider as show above.
Otherwise adjusting one voltage would upset the others.

V+ ^
|
<
VR1 ><--o
< \
| \
V- v \
o-- (To output buffer)
V+ ^
|
<
VR2 ><--o
<
|
V- v

Check this for inspiration :

http://www.wiseguysynth.com/larry/jlh-831/831.htm

--
André Majorel <URL:http://www.teaser.fr/~amajorel/>
Do not use this account for regular correspondence.
See the URL above for contact information.

Cgs synth

Rotary voltage selector

Rotary voltage selector

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Re: Rotary voltage selector

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