Magnetic force

[Don Y]

I have an optically-couple "supervisory port" on my
devices. A design requirement is that the outer surfaces
of the devices must be "wipe clean" -- no ridges or
grooves.

I mechanically attach the mating "cable" to the port
magnetically (an idea I stole from designing electric
power meters -- but, they aren't "wipe clean"!)

As I can't rely on any significant mechanical structures
to help maintain the attachment's position, that must
be guaranteed solely by the strength of the magnetic
bond.

I have a 1/4" dia glass "jewel" that is just barely convex
to protect the optical port and support light passage.
The slight bump helps locate the port as well as some small
assistance in keeping the mated "cable" positioned properly.

In no case can the needs of the port exceed a concentric
diameter of 1/2". I plan for the magnet to only be present
in the mating cable so its adhesion will be determined by
the metallic ring surrounding the jewel.

I figure I need to specify a magnet strong enough to
"support" (against the force of gravity exerted on the
mass of the cable) the cable in a horizontal position
(i.e., "mated to the ceiling"). And, to support the
cantilevered weight of the cable when mounted
vertically.

I may opt to implement the "cable" as a wireless dongle
if the weight of the cable assembly starts to compromise that
magnetic adherence.

I guess I also need to consider the magnetic force exerted
through the friction between the mating surfaces when
mounted vertically (so the cable doesn't "slide down the wall")

Anything else I should consider? I realize that the cable end
now will have a tendency to want to grab onto metallic objects
so have to factor that into my dongle vs. cable decision
(it's a lot easier to control the position of a dongle in
space than the end of a possibly *dangling* cable!)

I suspect the adhering "metal" piece has to be on the skin
of the device as the magnetic field falls off quickly with
distance -- diluting the ability of the cable to remain
EXACTLY where desired. A "decal" over the surface likely
would be tolerable...

[Liz Tuddenham]

Post by Don Y
I have an optically-couple "supervisory port" on my
devices. A design requirement is that the outer surfaces
of the devices must be "wipe clean" -- no ridges or
grooves.
I mechanically attach the mating "cable" to the port
magnetically (an idea I stole from designing electric
power meters -- but, they aren't "wipe clean"!)
As I can't rely on any significant mechanical structures
to help maintain the attachment's position, that must
be guaranteed solely by the strength of the magnetic
bond.
I have a 1/4" dia glass "jewel" that is just barely convex
to protect the optical port and support light passage.
The slight bump helps locate the port as well as some small
assistance in keeping the mated "cable" positioned properly.
In no case can the needs of the port exceed a concentric
diameter of 1/2". I plan for the magnet to only be present
in the mating cable so its adhesion will be determined by
the metallic ring surrounding the jewel.
I figure I need to specify a magnet strong enough to
"support" (against the force of gravity exerted on the
mass of the cable) the cable in a horizontal position
(i.e., "mated to the ceiling"). And, to support the
cantilevered weight of the cable when mounted
vertically.
I may opt to implement the "cable" as a wireless dongle
if the weight of the cable assembly starts to compromise that
magnetic adherence.
I guess I also need to consider the magnetic force exerted
through the friction between the mating surfaces when
mounted vertically (so the cable doesn't "slide down the wall")
Anything else I should consider? I realize that the cable end
now will have a tendency to want to grab onto metallic objects
so have to factor that into my dongle vs. cable decision
(it's a lot easier to control the position of a dongle in
space than the end of a possibly *dangling* cable!)
I suspect the adhering "metal" piece has to be on the skin
of the device as the magnetic field falls off quickly with
distance -- diluting the ability of the cable to remain
EXACTLY where desired. A "decal" over the surface likely
would be tolerable...

Would a rounded bump on the device be acceptable? A matching hollow in
the cable end could then locate over it.

Something like this:
Loading Image...

[Liz Tuddenham]

Liz Tuddenham <***@poppyrecords.invalid.invalid> wrote:

[...]

Post by Liz Tuddenham
http://www.poppyrecords.co.uk/other/Connector.gif

or this, for a stronger retaining force?

Loading Image...

[Don Y]

Post by Liz Tuddenham

Post by Don Y
I suspect the adhering "metal" piece has to be on the skin
of the device as the magnetic field falls off quickly with
distance -- diluting the ability of the cable to remain
EXACTLY where desired. A "decal" over the surface likely
would be tolerable...

Would a rounded bump on the device be acceptable? A matching hollow in
the cable end could then locate over it.

It would depend on how "rounded" the bump was. And, how
tightly the "insert" matched the "equipment" plane.

When not "mated", the "bumps" are most often touched
(think of them as buttons and indicators when not acting
as communication ports). E.g., the emitter normally
visibly indicates "status"; "touching" it acts to
invoke IDENTIFY/TRAP/RESET/POWER/SHUTDOWN functions.
So, the bump makes it easier to find with a fingertip
(otherwise, you have to be able to perceive the
difference between the glass of the jewel and the material
of the case)

Oils (and dirt) from hands will want to accumulate on those
surfaces. Easily wiping them clean has to remove ALL traces
of that crud (because the person cleaning them may not be
able to SEE them -- blind/visually impaired -- but, others
*will* and would notice how grimey it appears)

[Imagine being blind and someone asks to use your toilet...
are you ever *sure* that they don't come out totally
disgusted by what THEY saw that you *haven't*? <ick>]

Post by Liz Tuddenham
http://www.poppyrecords.co.uk/other/Connector.gif

That's sort of what I was thinking though I was imagining the
magnet on the cable end (because there can be many such
ports in close proximity to each other -- 5/8" apart, hence
the limit of 1/2" -- but only one cable end).

I imagined the bump as being the glass piece with the
*detector and emitter* behind it (internal to the
"equipment") and an annular ring surrounding/framing
the glass jewel. The ring magnet would be on the
cable end with an inner diameter just larger than
the glass jewel.

In the case of an attached *dongle*, there would be a
corresponding detector and emitter in the dongle.
For a cable, fiber could suffice over short distances
(else put the electronics on the end of the cable).

[Joe Gwinn]

On Fri, 20 Sep 2024 00:11:05 -0700, Don Y

Post by Don Y
I have an optically-couple "supervisory port" on my
devices. A design requirement is that the outer surfaces
of the devices must be "wipe clean" -- no ridges or
grooves.
I mechanically attach the mating "cable" to the port
magnetically (an idea I stole from designing electric
power meters -- but, they aren't "wipe clean"!)
As I can't rely on any significant mechanical structures
to help maintain the attachment's position, that must
be guaranteed solely by the strength of the magnetic
bond.

This approach will attract and hold magnetic debris, like rust and
iron filings. Is that a problem, or is wiping enough? If the magnets
are strong enough, debris removal may be difficult to do in practice.

Joe Gwinn

Post by Don Y
I have a 1/4" dia glass "jewel" that is just barely convex
to protect the optical port and support light passage.
The slight bump helps locate the port as well as some small
assistance in keeping the mated "cable" positioned properly.
In no case can the needs of the port exceed a concentric
diameter of 1/2". I plan for the magnet to only be present
in the mating cable so its adhesion will be determined by
the metallic ring surrounding the jewel.
I figure I need to specify a magnet strong enough to
"support" (against the force of gravity exerted on the
mass of the cable) the cable in a horizontal position
(i.e., "mated to the ceiling"). And, to support the
cantilevered weight of the cable when mounted
vertically.
I may opt to implement the "cable" as a wireless dongle
if the weight of the cable assembly starts to compromise that
magnetic adherence.
I guess I also need to consider the magnetic force exerted
through the friction between the mating surfaces when
mounted vertically (so the cable doesn't "slide down the wall")
Anything else I should consider? I realize that the cable end
now will have a tendency to want to grab onto metallic objects
so have to factor that into my dongle vs. cable decision
(it's a lot easier to control the position of a dongle in
space than the end of a possibly *dangling* cable!)
I suspect the adhering "metal" piece has to be on the skin
of the device as the magnetic field falls off quickly with
distance -- diluting the ability of the cable to remain
EXACTLY where desired. A "decal" over the surface likely
would be tolerable...

[Don Y]

Post by Joe Gwinn
On Fri, 20 Sep 2024 00:11:05 -0700, Don Y

Post by Don Y
I have an optically-couple "supervisory port" on my
devices. A design requirement is that the outer surfaces
of the devices must be "wipe clean" -- no ridges or
grooves.
I mechanically attach the mating "cable" to the port
magnetically (an idea I stole from designing electric
power meters -- but, they aren't "wipe clean"!)
As I can't rely on any significant mechanical structures
to help maintain the attachment's position, that must
be guaranteed solely by the strength of the magnetic
bond.

This approach will attract and hold magnetic debris, like rust and
iron filings. Is that a problem, or is wiping enough? If the magnets
are strong enough, debris removal may be difficult to do in practice.

Are you expecting the non-magnet surface to assume a
magnetic state, over time?

The actual magnet will be on the cable end so the
"wipe clean" surface will not inherently be magnetized.
And, the cable end should be easier to manipulate, "scrub",
etc (even REPLACE) as it is "portable".

[Joe Gwinn]

On Fri, 20 Sep 2024 12:26:44 -0700, Don Y

Post by Don Y

Post by Joe Gwinn
On Fri, 20 Sep 2024 00:11:05 -0700, Don Y

Post by Don Y
I have an optically-couple "supervisory port" on my
devices. A design requirement is that the outer surfaces
of the devices must be "wipe clean" -- no ridges or
grooves.
I mechanically attach the mating "cable" to the port
magnetically (an idea I stole from designing electric
power meters -- but, they aren't "wipe clean"!)
As I can't rely on any significant mechanical structures
to help maintain the attachment's position, that must
be guaranteed solely by the strength of the magnetic
bond.

This approach will attract and hold magnetic debris, like rust and
iron filings. Is that a problem, or is wiping enough? If the magnets
are strong enough, debris removal may be difficult to do in practice.

Are you expecting the non-magnet surface to assume a
magnetic state, over time?

Not if the non-magnet side is soft enough magnetically.

Post by Don Y
The actual magnet will be on the cable end so the
"wipe clean" surface will not inherently be magnetized.
And, the cable end should be easier to manipulate, "scrub",
etc (even REPLACE) as it is "portable".

That'll work so long as the magnet isn't too strong.

A good way to clean stuff off a magnet pole is adhesive tape.

I'd take a rare earth magnet and roll it around on the floor of the
garage, and see what you catch.

Joe Gwinn

[Don Y]

Post by Joe Gwinn

Post by Don Y
The actual magnet will be on the cable end so the
"wipe clean" surface will not inherently be magnetized.
And, the cable end should be easier to manipulate, "scrub",
etc (even REPLACE) as it is "portable".

That'll work so long as the magnet isn't too strong.

This argues AGAINST the use of a "dongle" as that would likely
find itself stored in pockets and other places where detritus
could accumulate.

Post by Joe Gwinn
A good way to clean stuff off a magnet pole is adhesive tape.

I usually use duct tape to pick up steel filings/shavings.
The cloth backing seems to "absorb" the bits better.

Post by Joe Gwinn
I'd take a rare earth magnet and roll it around on the floor of the
garage, and see what you catch.

The environment tends not to include metal bits -- unless
devices are installed in *metal* Jboxes that may have been
drilled for mounting.

Dirt (from hands) is more likely to be the contaminant.
And, will find its way into the smallest of cracks/seams.
(consider how tedious it is to clean a mouse, keyboard,
etc. so that it truly looks "clean enough to seem new")

I'd thought about disposable/replaceable "double-sticky"
pads that could be used to adhere the cable end to the
"equipment". But, that would be tedious when you want
to connect to multiple devices and have to keep peeling
old pads off. And, would likely leave adhesive residue
that would attract MORE than just dirt/oils from hands.

I'd also thought about semi-adhesive strips to deploy to PULL
the crud off of these surfaces but that assumes folks are aware
of how dirty the "look" AND how willing they are to maintain a
supply of "cleaning strips".

[Liz Tuddenham]

Joe Gwinn <***@comcast.net> wrote:

[...]

Post by Joe Gwinn
A good way to clean stuff off a magnet pole is adhesive tape.

If the surface is too convoluted for the tape to work, there is a
product in the UK called "Copydex", which is sold as a carpet glue but
can be used to remove debris from a magnet. It is an emulsified latex
solution which doesn't stick well to metal surfaces and can be peeled
off easily.

You apply the Copydex thickly over the surface to be cleaned - and then
wait. Eventually the milky white liquid dries to complete transparency,
then it is strong enough to be peeled off, bringing the debris with it.

[Don Y]

Post by Liz Tuddenham
[...]

Post by Joe Gwinn
A good way to clean stuff off a magnet pole is adhesive tape.

If the surface is too convoluted for the tape to work, there is a
product in the UK called "Copydex", which is sold as a carpet glue but
can be used to remove debris from a magnet. It is an emulsified latex
solution which doesn't stick well to metal surfaces and can be peeled
off easily.
You apply the Copydex thickly over the surface to be cleaned - and then
wait. Eventually the milky white liquid dries to complete transparency,
then it is strong enough to be peeled off, bringing the debris with it.

I would imagine any of the "silicone caulks" would work
equally well.

The downside with any of these is that there is a
"drying time". I don't imagine the folks using
this bit of kit would sit around waiting before
reusing (or retiring) it. <frown> Imagine having
to similarly clean a 'scope probe between uses...

[Liz Tuddenham]

Post by Don Y

Post by Liz Tuddenham
[...]

Post by Joe Gwinn
A good way to clean stuff off a magnet pole is adhesive tape.

If the surface is too convoluted for the tape to work, there is a
product in the UK called "Copydex", which is sold as a carpet glue but
can be used to remove debris from a magnet. It is an emulsified latex
solution which doesn't stick well to metal surfaces and can be peeled
off easily.
You apply the Copydex thickly over the surface to be cleaned - and then
wait. Eventually the milky white liquid dries to complete transparency,
then it is strong enough to be peeled off, bringing the debris with it.

I would imagine any of the "silicone caulks" would work
equally well.

It needs to peel off easily. The silicone caulk I have used has always
stuck very firmly to metal.

Post by Don Y
The downside with any of these is that there is a
"drying time". I don't imagine the folks using
this bit of kit would sit around waiting before
reusing (or retiring) it. <frown> Imagine having
to similarly clean a 'scope probe between uses...

Yes, this is very much a specialist tool for getting metal debris out of
magnet gaps in moving coil meter movements or disc cutterheads, where
time is not a major factor.

[Don Y]

Post by Liz Tuddenham

Post by Don Y
I would imagine any of the "silicone caulks" would work
equally well.

It needs to peel off easily. The silicone caulk I have used has always
stuck very firmly to metal.

I think if you were dealing with something "fine" you
would have a problem. But, if you can firmly grasp the
one piece and peal back the caulk, it doesn't seem to be
a problem.

I often use this to make molds from "positive" articles
instead of a more solid-setting material (e.g., plaster or wax).

Post by Liz Tuddenham

Post by Don Y
The downside with any of these is that there is a
"drying time". I don't imagine the folks using
this bit of kit would sit around waiting before
reusing (or retiring) it. <frown> Imagine having
to similarly clean a 'scope probe between uses...

Yes, this is very much a specialist tool for getting metal debris out of
magnet gaps in moving coil meter movements or disc cutterheads, where
time is not a major factor.

Different use pattern. The communication cable is used
most like a 'scope probe -- attach to one access point,
examine/interact data stream, detach and move to the next.

I use it for diagnostics, debugging and installing "secrets".
As it is not uncommon for folks (nowadays) to exploit
"internal/secret" access ports (e.g., "to start a shell on
tty0..."), having something other than a 4 pin header to which
you can attach a TTL-level serial device raises the bar a bit.
(having all of the comms over that port encrypted makes it
virtually unattainable!) And, of course, not having to
perforate the case to provide access to same is a win as well!

None of these are activities where the user would have an
abundance of patience...

[Joe Gwinn]

Post by Liz Tuddenham
[...]

Post by Joe Gwinn
A good way to clean stuff off a magnet pole is adhesive tape.

If the surface is too convoluted for the tape to work, there is a
product in the UK called "Copydex", which is sold as a carpet glue but
can be used to remove debris from a magnet. It is an emulsified latex
solution which doesn't stick well to metal surfaces and can be peeled
off easily.
You apply the Copydex thickly over the surface to be cleaned - and then
wait. Eventually the milky white liquid dries to complete transparency,
then it is strong enough to be peeled off, bringing the debris with it.

Sounds like a modern equivalent to soft Collodion, which is widely
used to clean optical surfaces.

.<https://en.wikipedia.org/wiki/Collodion>


Joe Gwinn