Is there any Multi Turn LOG/AUDIO pots?? If not, how can I m

M

Mike Beauchamp

Guest
Hey all..
I'm working on something where I need a highly precise Potentiometer but it
has to be LOG. I want to use a multiple turn pot (for the resolution), but I
can't find any that are listed as LOG, only LINEAR? Does such a thing
exist?

I want the Potentimeter to be 100K.. and according to a few sites I can make
it close to LOG by adding a 35K resistor.

But, on the "beginners guide to pots", it shows a graph:
http://sound.westhost.com/pots.htm

and it ends up being more S shaped than log, but lower down, it shows a dual
ganged volume balance control using a linear pot and the resistor, and the
curve definately looks more log to me.

Mike
http://mikebeauchamp.com
 
Just to clarify more, because I seemed to have confused myself looking at
thsoe diagrams since they were in a Voltage Divider situation..

My situation is this.. between two contacts, I need to vary the resistance
in in a Log function, compared to the Linear turning of the potentiometer.
Just hooking one edge of the pot up to one contact and the other contact to
the wiper of a LOG pot would be absolutely perfect for me. BUT, regular log
potentiometers don't seem to offere the resolution and precision that I
need..

Mike
http://mikebeauchamp.com



"Mike Beauchamp" <newsgroups@mikebeauchamp.com> wrote in message
news:btct450tik@enews2.newsguy.com...
Hey all..
I'm working on something where I need a highly precise Potentiometer but
it
has to be LOG. I want to use a multiple turn pot (for the resolution), but
I
can't find any that are listed as LOG, only LINEAR? Does such a thing
exist?

I want the Potentimeter to be 100K.. and according to a few sites I can
make
it close to LOG by adding a 35K resistor.

But, on the "beginners guide to pots", it shows a graph:
http://sound.westhost.com/pots.htm

and it ends up being more S shaped than log, but lower down, it shows a
dual
ganged volume balance control using a linear pot and the resistor, and the
curve definately looks more log to me.

Mike
http://mikebeauchamp.com
Click to expand...
 
On Mon, 5 Jan 2004 18:48:19 -0500, "Mike Beauchamp"
<newsgroups@mikebeauchamp.com> wrote:

Hey all..
I'm working on something where I need a highly precise Potentiometer but it
has to be LOG. I want to use a multiple turn pot (for the resolution), but I
can't find any that are listed as LOG, only LINEAR? Does such a thing
exist?
Click to expand...
---
I don't know, but if you can't find one you could always use a
multi-turn precision linear pot, an ADC, a lookup table, and a DAC to
get whatever transfer function you wanted out of the pot.

--
John Fields
 
Mike Beauchamp wrote:
Just to clarify more, because I seemed to have confused myself looking at
thsoe diagrams since they were in a Voltage Divider situation..

My situation is this.. between two contacts, I need to vary the resistance
in in a Log function, compared to the Linear turning of the potentiometer.
Just hooking one edge of the pot up to one contact and the other contact to
the wiper of a LOG pot would be absolutely perfect for me. BUT, regular log
potentiometers don't seem to offere the resolution and precision that I
need..

Mike
http://mikebeauchamp.com
Click to expand...
How about using a gear reduction drive with a standard 270° log pot?

--
We now return you to our normally scheduled programming.

Take a look at this! ;-)
http://home.earthlink.net/~mike.terrell/photos.html

Michael A. Terrell
Central Florida
 
"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
news:3FFA4E3D.43B7BCA2@earthlink.net...
Mike Beauchamp wrote:

Just to clarify more, because I seemed to have confused myself looking
at
thsoe diagrams since they were in a Voltage Divider situation..

My situation is this.. between two contacts, I need to vary the
resistance
in in a Log function, compared to the Linear turning of the
potentiometer.
Just hooking one edge of the pot up to one contact and the other contact
to
the wiper of a LOG pot would be absolutely perfect for me. BUT, regular
log
potentiometers don't seem to offere the resolution and precision that I
need..

Mike
http://mikebeauchamp.com

How about using a gear reduction drive with a standard 270° log pot?

Michael A. Terrell
Central Florida
Click to expand...
It would still be linear, but with a different slope.

Possibly a large off center pulley where the rate would change depending on
the position of rotation similar to some of the exercise machines
(nautilus)?

Louis--
*********************************************
Remove the two fish in address to respond
 
"John Fields" <jfields@austininstruments.com> wrote in message
news:cfdkvvkeq0jkk96lige879ocfn713trvq7@4ax.com...
On Mon, 5 Jan 2004 18:48:19 -0500, "Mike Beauchamp"
newsgroups@mikebeauchamp.com> wrote:

Hey all..
I'm working on something where I need a highly precise Potentiometer but
it
has to be LOG. I want to use a multiple turn pot (for the resolution),
but I
can't find any that are listed as LOG, only LINEAR? Does such a thing
exist?

---
I don't know, but if you can't find one you could always use a
multi-turn precision linear pot, an ADC, a lookup table, and a DAC to
get whatever transfer function you wanted out of the pot.

--
John Fields
Click to expand...
This solution would take a higher degree of ability to implement, but is
spot on, and could result in a very precise result depending on the care in
its implementation. Another positive aspect of this method would be the
ability to tune the output for any anomalies in the surrounding process.

Louis--
*********************************************
Remove the two fish in address to respond
 
On Tue, 06 Jan 2004 21:24:35 GMT, "Louis Bybee"
<louistroutbybee@comcasttrout.net> wrote:

"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
news:3FFA4E3D.43B7BCA2@earthlink.net...
Mike Beauchamp wrote:

Just to clarify more, because I seemed to have confused myself looking
at
thsoe diagrams since they were in a Voltage Divider situation..

My situation is this.. between two contacts, I need to vary the
resistance
in in a Log function, compared to the Linear turning of the
potentiometer.
Just hooking one edge of the pot up to one contact and the other contact
to
the wiper of a LOG pot would be absolutely perfect for me. BUT, regular
log
potentiometers don't seem to offere the resolution and precision that I
need..

Mike
http://mikebeauchamp.com

How about using a gear reduction drive with a standard 270° log pot?

Michael A. Terrell
Central Florida

It would still be linear, but with a different slope.
Click to expand...
---
If you start with a log pot how would a linear gear reduction drive make
it be "still" linear?
---

--
John Fields
 
Louis Bybee wrote:
"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
news:3FFA4E3D.43B7BCA2@earthlink.net...

How about using a gear reduction drive with a standard 270° log pot?
Click to expand...
^^^^^^^

^^^^^^^

^^^^^^^
Michael A. Terrell
Central Florida

It would still be linear, but with a different slope.

Possibly a large off center pulley where the rate would change depending on
the position of rotation similar to some of the exercise machines
(nautilus)?

Louis--
Click to expand...
Louis, I stated that you need a log pot, not a linear one. Also, you
should put some mechanical stops like a notched wheel and a heavy steel
pin or block to prevent damaging the pot. The gear reduction drive will
have a lot more toque than a straight shaft.

--
We now return you to our normally scheduled programming.

Take a look at this little cutie! ;-)
http://home.earthlink.net/~mike.terrell/photos.html

Michael A. Terrell
Central Florida
 
"Louis Bybee" <louistroutbybee@comcasttrout.net> wrote in message news:<FNFKb.760312$Tr4.2159351@attbi_s03>...
"John Fields" <jfields@austininstruments.com> wrote in message
news:cfdkvvkeq0jkk96lige879ocfn713trvq7@4ax.com...
On Mon, 5 Jan 2004 18:48:19 -0500, "Mike Beauchamp"
newsgroups@mikebeauchamp.com> wrote:

Hey all..
I'm working on something where I need a highly precise Potentiometer but
it
has to be LOG. I want to use a multiple turn pot (for the resolution),
but I
can't find any that are listed as LOG, only LINEAR? Does such a thing
exist?

---
I don't know, but if you can't find one you could always use a
multi-turn precision linear pot, an ADC, a lookup table, and a DAC to
get whatever transfer function you wanted out of the pot.

--
John Fields

This solution would take a higher degree of ability to implement, but is
spot on, and could result in a very precise result depending on the care in
its implementation. Another positive aspect of this method would be the
ability to tune the output for any anomalies in the surrounding process.

Louis--
*********************************************
Remove the two fish in address to respond
Click to expand...
If I needed that degree of control, I'd skip the pot and ADC and use a
shaft encoder to set the address into the lookup table. Could also
have a digital readout and would not have any discontinuities (pots
get noisy eventually). The stability would be limited to the
performance of the voltage ref into the DAC.
GG
 
On 6 Jan 2004 19:22:52 -0800, stratus46@yahoo.com (Glenn Gundlach)
wrote:


If I needed that degree of control, I'd skip the pot and ADC and use a
shaft encoder to set the address into the lookup table. Could also
have a digital readout and would not have any discontinuities (pots
get noisy eventually). The stability would be limited to the
performance of the voltage ref into the DAC.
Click to expand...
---
Excellent idea!

Plus, if there's no need for an analog output he could make the output
of the lookup table whatever he wants and be done with the DAC and
reference.

--
John Fields
 
"Louis Bybee" <louistroutbybee@comcasttrout.net> wrote in message news:<FNFKb.760312$Tr4.2159351@attbi_s03>...

This solution would take a higher degree of ability to implement, but is
spot on, and could result in a very precise result depending on the care in
its implementation.
Click to expand...

Louis, with a sentence like that you should consider going into politics!

niftydog
 
I need a highly precise Potentiometer but it has to be LOG.
I want to use a multiple turn pot (for the resolution),
but I can't find any that are listed as LOG, only LINEAR?
Does such a thing exist?

I want the Potentimeter to be 100K.. and according to a few sites
I can make it close to LOG by adding a 35K resistor.

But, on the "beginners guide to pots", it shows a graph:
http://sound.westhost.com/pots.htm

and it ends up being more S shaped than log, but lower down, it shows
a dual ganged volume balance control using a linear pot and the resistor,
and the curve definately looks more log to me.

Mike Beauchamp

Yup. I've got one of these DIY-shunts on my Grandpa's old portable radio.
Click to expand...
The results are useable. It has an exponential response.
What the exact curve is isn't critical.

You'll notice that the referenced page is about AUDIO.
What's that they say about good enough for rock'n'roll?
 
On Mon, 5 Jan 2004 18:59:40 -0500, "Mike Beauchamp"
<newsgroups@mikebeauchamp.com> wrote:

Just to clarify more, because I seemed to have confused myself looking at
thsoe diagrams since they were in a Voltage Divider situation..

My situation is this.. between two contacts, I need to vary the resistance
in in a Log function, compared to the Linear turning of the potentiometer.
Just hooking one edge of the pot up to one contact and the other contact to
the wiper of a LOG pot would be absolutely perfect for me. BUT, regular log
potentiometers don't seem to offere the resolution and precision that I
need..
Click to expand...
---
What _exactly_ are you looking for in terms of resolution and precision?

--
John Fields
 
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