Designing a special knob
BACKGROUND:
For a Christmas gift I'm making an electronics project in a neat
enclosure. It includes the facility for choosing one of 24 options. That
currently uses a 12 way rotary switch, requiring wires to 12 inputs of a
micro controller unit (MCU). That works. But I want to reduce the size
of the MCU, the wiring, and the case. I've therefore redesigned it so
that the initial choice is instead made by turning the knob of a
potentiometer to one of 24 angles. That works too. But I'm seeking help
on (at least!) labelling the knob positions please.
I could relearn some Inkscape or perhaps use my familiar PaintShop Pro.
And stick the paper or card result around the knob. But Im considering
OpenSCAD, partly because that will let me play with my Ender 3 Pro 3D
printer. But it would also deliver a finished and labelled knob as the
end result. And the basis for other future projects (my hobby).
DETAILS:
The dial needs 24 small labels marked 01 ,02... 24. Accurately
positioned around the circumference of a circle of about 30 mm diameter.
A pointed knob on a potentiometers spindle swings through about
315/320°. Hard to measure precisely; my best guess is 360-45 = 315°.
Here's a sketch to make it clearer.
https://www.dropbox.com/scl/fi/pcaiwwi397fbs59f4ouc8/dials.JPG?rlkey=7rv7035pezttuen6govbkstx7&raw=1
The 3D printed version would clearly need tiny labels, within an arc of
about 315/24 = 13°; so I might compromise with 1, 2, 4, 6, etc. (The
first user choice is '1', not '0'.)
Im struggling in particular with placing the numbers radially and
vertically at those positions. Any help would be appreciated please.
Terry, UK
Note that "tiny" and "3d printed" do not go well together. 3DP text
needs to be fairly big, relative to normal printed text.
Also: potentiometers don't click. That might be a UI problem depending
on your application.
Here's something to get you started.
n = 24;
gap = 40;
r = 30;
fontsize = 3;
// Note that angles naturally have zero being along the positive X axis,
// with positive angles counterclockwise from there. This leads to a couple
// of offsets in the functions, and negating the angle in one of them.
// Note that (i-1)/(n-1)*(arc size) maps i=1 to the start of the arc
// and i=n to the end of the arc.
// Sketch 1: numbers around the outside of a knob
// Given a number, return its angle.
function angle1(i) = 270 - gap/2 - (i-1)/(n-1)*(360-gap);
for (i=[1:n]) {
angle = angle1(i);
// Note that the two rotations cancel each other out, leaving the text upright.
rotate(angle) translate([r,0])
rotate(-angle) text(str(i), size=fontsize, halign="center", valign="center");
}
// Sketch 2: numbers around the top of a knob
// Given a number, return its angle.
function angle2(i) = 90 + (i-1)/(n-1)*(360-gap);
translate([100,0]) for (i=[1:n]) {
rotate(angle2(i)) translate([r,0]) rotate(-90) text(str(i), size=fontsize, halign="center", valign="center");
}
You could make a potentiometer click by printing a wheel with 24 detents
and pushing a small ball against it with a spring. You could have that
mounted behind the panel as most pots have long shafts that you cut to
length.
On Thu, 12 Dec 2024 at 19:45, Jordan Brown via Discuss <
discuss@lists.openscad.org> wrote:
Note that "tiny" and "3d printed" do not go well together. 3DP text needs
to be fairly big, relative to normal printed text.
Also: potentiometers don't click. That might be a UI problem depending
on your application.
Here's something to get you started.
n = 24;
gap = 40;
r = 30;
fontsize = 3;
// Note that angles naturally have zero being along the positive X axis,
// with positive angles counterclockwise from there. This leads to a couple
// of offsets in the functions, and negating the angle in one of them.
// Note that (i-1)/(n-1)*(arc size) maps i=1 to the start of the arc
// and i=n to the end of the arc.
// Sketch 1: numbers around the outside of a knob
// Given a number, return its angle.
function angle1(i) = 270 - gap/2 - (i-1)/(n-1)*(360-gap);
for (i=[1:n]) {
angle = angle1(i);
// Note that the two rotations cancel each other out, leaving the text upright.
rotate(angle) translate([r,0])
rotate(-angle) text(str(i), size=fontsize, halign="center", valign="center");
}
// Sketch 2: numbers around the top of a knob
// Given a number, return its angle.
function angle2(i) = 90 + (i-1)/(n-1)*(360-gap);
translate([100,0]) for (i=[1:n]) {
rotate(angle2(i)) translate([r,0]) rotate(-90) text(str(i), size=fontsize, halign="center", valign="center");
}
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On 12/12/24 13:55, Terry via Discuss wrote:
BACKGROUND:
For a Christmas gift I'm making an electronics project in a neat
enclosure. It includes the facility for choosing one of 24 options. That
currently uses a 12 way rotary switch, requiring wires to 12 inputs of a
micro controller unit (MCU). That works. But I want to reduce the size
of the MCU, the wiring, and the case. I've therefore redesigned it so
that the initial choice is instead made by turning the knob of a
potentiometer to one of 24 angles. That works too. But I'm seeking help
on (at least!) labelling the knob positions please.
I could relearn some Inkscape or perhaps use my familiar PaintShop Pro.
And stick the paper or card result around the knob. But I’m considering
OpenSCAD, partly because that will let me play with my Ender 3 Pro 3D
printer. But it would also deliver a finished and labelled knob as the
end result. And the basis for other future projects (my hobby).
DETAILS:
The dial needs 24 small labels marked ‘01’ ,’02’... ’24’. Accurately
positioned around the circumference of a circle of about 30 mm diameter.
A pointed knob on a potentiometer’s spindle swings through about
315/320°. Hard to measure precisely; my best guess is 360-45 = 315°.
Here's a sketch to make it clearer.
https://www.dropbox.com/scl/fi/pcaiwwi397fbs59f4ouc8/dials.JPG?rlkey=7rv7035pezttuen6govbkstx7&raw=1
The 3D printed version would clearly need tiny labels, within an arc of
about 315/24 = 13°; so I might compromise with 1, 2, 4, 6, etc. (The
first user choice is '1', not '0'.)
I’m struggling in particular with placing the numbers radially and
vertically at those positions. Any help would be appreciated please.
Terry, UK
1: You would be asking that 3d printer for about 5 times the resolution
it can do unless you have an engraving laser on it. Text at least 7mm
high is about as small as they can do in FDM mode and remain legible.
An optical that uses photo resins can do smaller but I've zero
experience with those.
2: Most potentiometers have an active range under 300 degrees as the end
of the circular element has little to no change in the resistance for
the 10+% percentage from the end stops. Perhaps a pair of pushbuttons,
controlling a digital up/down counter in the arduino code would be
better as you could then use the counter reading for direct control. A
2 digit lcd display could serve as the display, probably for less than a
decent pot costs.
Cheers, Gene Heskett, CET.
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
On Thu, Dec 12, 2024 at 10:55 AM Terry via Discuss <
discuss@lists.openscad.org> wrote:
BACKGROUND:
For a Christmas gift I'm making an electronics project in a neat
enclosure. It includes the facility for choosing one of 24 options. That
currently uses a 12 way rotary switch, requiring wires to 12 inputs of a
micro controller unit (MCU). That works. But I want to reduce the size
of the MCU, the wiring, and the case. I've therefore redesigned it so
that the initial choice is instead made by turning the knob of a
potentiometer to one of 24 angles. That works too. But I'm seeking help
on (at least!) labelling the knob positions please.
I could relearn some Inkscape or perhaps use my familiar PaintShop Pro.
And stick the paper or card result around the knob. But I’m considering
OpenSCAD, partly because that will let me play with my Ender 3 Pro 3D
printer. But it would also deliver a finished and labelled knob as the
end result. And the basis for other future projects (my hobby).
Veering off topic:
I'm surprised you aren't using a rotary encoder if you are worried about
the number of wires
https://www.digikey.com/en/products/detail/bourns-inc/PEC11R-4220F-S0024/4499660
- $2.20 something like this gives you clear clockwise/counter clockwise
signals, so as long as the device has power it can just add or subtract to
get to the desired setting.
A common technique is to print the numbers, mirror image, onto
transparency, so when the transparent plastic is cut to size and attached
it protects the ink on the underside.
On Thu, 12 Dec 2024 19:54:58 +0000, you wrote:
You could make a potentiometer click by printing a wheel with 24 detents
and pushing a small ball against it with a spring. You could have that
mounted behind the panel as most pots have long shafts that you cut to
length.
Thanks, that's a clever idea! I may well try it for a future project
that's dependent on a pot's position. But for this particular one I've
used another novel solution. The position reached within a set time
after power up is accepted, and spoken by an MP3 player. It's working
quite well on test. So I'm now hoping to use Jordan's labels (on either
the case or knob perimeter), PLUS a 1 sec playback of that position.##
I'm not sure mounting the detent inside would be possible. Apart
from space restrictions, how would the pot spindle then be easily
secured to the case with its thread and bolt? On top seems the way to
go.
Which would be way OTT; only possible because the project ('Sleep
Fader') has the main function of playing the choice of 24 MP3s.
P.S: My original 12W rotary switch approach had no labels, relying on
counting from position 1 (plus a supplementary toggle switch to get
choices 13 to 24.)
The pot would be mounted on a bracket behind the panel with just its shaft
poking through. That is often how they are mounted in equipment so you
don't have the nut on the panel and the knob can then be much closer to the
panel.
I have disassembled a couple of Chinese solder stations that had dual
potentiometers to set the temperature of the iron and the hot air gun. One
track of the pots simply drove 3 digit voltmeters to display the target
temperature and the other track was an analogue temperature controller.
Crazy.
I repurposed one as an IOT dummy load with autoranging ammeter and
voltmeters.
[image: IMG_20211005_095515156_HDR.jpg]
I used a rotary encoder to change the current setting or I can set it via a
web page or a Python script.
On Thu, 12 Dec 2024 at 21:45, Terry via Discuss discuss@lists.openscad.org
wrote:
On Thu, 12 Dec 2024 19:54:58 +0000, you wrote:
You could make a potentiometer click by printing a wheel with 24 detents
and pushing a small ball against it with a spring. You could have that
mounted behind the panel as most pots have long shafts that you cut to
length.
Thanks, that's a clever idea! I may well try it for a future project
that's dependent on a pot's position. But for this particular one I've
used another novel solution. The position reached within a set time
after power up is accepted, and spoken by an MP3 player. It's working
quite well on test. So I'm now hoping to use Jordan's labels (on either
the case or knob perimeter), PLUS a 1 sec playback of that position.##
I'm not sure mounting the detent inside would be possible. Apart
from space restrictions, how would the pot spindle then be easily
secured to the case with its thread and bolt? On top seems the way to
go.
Which would be way OTT; only possible because the project ('Sleep
Fader') has the main function of playing the choice of 24 MP3s.
P.S: My original 12W rotary switch approach had no labels, relying on
counting from position 1 (plus a supplementary toggle switch to get
choices 13 to 24.)
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To unsubscribe send an email to discuss-leave@lists.openscad.org
On Thu, 12 Dec 2024 13:18:50 -0800, you wrote:
On Thu, Dec 12, 2024 at 10:55?AM Terry via Discuss <
discuss@lists.openscad.org> wrote:
BACKGROUND:
For a Christmas gift I'm making an electronics project in a neat
enclosure. It includes the facility for choosing one of 24 options. That
currently uses a 12 way rotary switch, requiring wires to 12 inputs of a
micro controller unit (MCU). That works. But I want to reduce the size
of the MCU, the wiring, and the case. I've therefore redesigned it so
that the initial choice is instead made by turning the knob of a
potentiometer to one of 24 angles. That works too. But I'm seeking help
on (at least!) labelling the knob positions please.
I could relearn some Inkscape or perhaps use my familiar PaintShop Pro.
And stick the paper or card result around the knob. But Im considering
OpenSCAD, partly because that will let me play with my Ender 3 Pro 3D
printer. But it would also deliver a finished and labelled knob as the
end result. And the basis for other future projects (my hobby).
Veering off topic:
I'm surprised you aren't using a rotary encoder if you are worried about
the number of wires
https://www.digikey.com/en/products/detail/bourns-inc/PEC11R-4220F-S0024/4499660
- $2.20 something like this gives you clear clockwise/counter clockwise
signals, so as long as the device has power it can just add or subtract to
get to the desired setting.
A common technique is to print the numbers, mirror image, onto
transparency, so when the transparent plastic is cut to size and attached
it protects the ink on the underside.
Thanks David. Not sure I see the practicality of a rotary encoder. What
would be its trigger? Magnetic? Optical (e.g IR) ? Reflective? And the
mechanics of all that? And how would the position be displayed? Plus
extra code (see my reply to Gene re the aTTiny85.)
But I'm very interested in your other suggestion. Could you say a bit
more about it please? Are you talking about printing (mirrored) onto a
transparent sheet with an inkjet printer? Special non-smudge?
Terry
You can get little rotary encoders that look like a pot but they click and
give quadrature outputs and you can press them as well. So you could use
three inputs to an MCU and a two digit LED to display the position.
Some are very poorly made and give loads of bounce though.
On Thu, 12 Dec 2024 at 22:30, Terry via Discuss discuss@lists.openscad.org
wrote:
On Thu, 12 Dec 2024 13:18:50 -0800, you wrote:
On Thu, Dec 12, 2024 at 10:55?AM Terry via Discuss <
discuss@lists.openscad.org> wrote:
BACKGROUND:
For a Christmas gift I'm making an electronics project in a neat
enclosure. It includes the facility for choosing one of 24 options. That
currently uses a 12 way rotary switch, requiring wires to 12 inputs of a
micro controller unit (MCU). That works. But I want to reduce the size
of the MCU, the wiring, and the case. I've therefore redesigned it so
that the initial choice is instead made by turning the knob of a
potentiometer to one of 24 angles. That works too. But I'm seeking help
on (at least!) labelling the knob positions please.
I could relearn some Inkscape or perhaps use my familiar PaintShop Pro.
And stick the paper or card result around the knob. But I’m considering
OpenSCAD, partly because that will let me play with my Ender 3 Pro 3D
printer. But it would also deliver a finished and labelled knob as the
end result. And the basis for other future projects (my hobby).
Veering off topic:
I'm surprised you aren't using a rotary encoder if you are worried about
the number of wires
- $2.20 something like this gives you clear clockwise/counter clockwise
signals, so as long as the device has power it can just add or subtract to
get to the desired setting.
A common technique is to print the numbers, mirror image, onto
transparency, so when the transparent plastic is cut to size and attached
it protects the ink on the underside.
Thanks David. Not sure I see the practicality of a rotary encoder. What
would be its trigger? Magnetic? Optical (e.g IR) ? Reflective? And the
mechanics of all that? And how would the position be displayed? Plus
extra code (see my reply to Gene re the aTTiny85.)
But I'm very interested in your other suggestion. Could you say a bit
more about it please? Are you talking about printing (mirrored) onto a
transparent sheet with an inkjet printer? Special non-smudge?
Terry
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To unsubscribe send an email to discuss-leave@lists.openscad.org
If you have a surface mounted pot, then mount it on a pcb, and a hole in
the case for the shaft and knob on the outside. You can fit a disc on
the shaft, below the front panel, with the printed numbers showing
through a hole in the panel, you can make the disc large enough to see
the numbers., add detents if you wish. Cover the front panel with a
piece of acrylic sheet.
if you haven't got a surface mounted pot, then print or fabricate a
bracket/whatever, to hold the pot below the front panel.
But you can get for not many pennies, small OLED displays, and software
to run them on arduino/whatever.
On 12/12/2024 21:45, Terry via Discuss wrote:
On Thu, 12 Dec 2024 19:54:58 +0000, you wrote:
You could make a potentiometer click by printing a wheel with 24 detents
and pushing a small ball against it with a spring. You could have that
mounted behind the panel as most pots have long shafts that you cut to
length.
Thanks, that's a clever idea! I may well try it for a future project
that's dependent on a pot's position. But for this particular one I've
used another novel solution. The position reached within a set time
after power up is accepted, and spoken by an MP3 player. It's working
quite well on test. So I'm now hoping to use Jordan's labels (on either
the case or knob perimeter), PLUS a 1 sec playback of that position.##
I'm not sure mounting the detent inside would be possible. Apart
from space restrictions, how would the pot spindle then be easily
secured to the case with its thread and bolt? On top seems the way to
go.
Which would be way OTT; only possible because the project ('Sleep
Fader') has the main function of playing the choice of 24 MP3s.
P.S: My original 12W rotary switch approach had no labels, relying on
counting from position 1 (plus a supplementary toggle switch to get
choices 13 to 24.)
OpenSCAD mailing list
To unsubscribe send an email to discuss-leave@lists.openscad.org