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PICList Thread
'[PICLIST] Need some switch ideas'
2001\04\03@123133 by Steve Nordhauser

picon face
I am developing an underwater digital camcorder and need some suggestions
on pushbutton switches for the body.  The requirements are that they are fairly
small (1/4" to 1/2"), sealed to 200ft, can handle harsh environments (sand and
sea water) and provide contact as long as depressed (unlike piezos which put
out a single pulse).  They should not draw much current when open and can be
read by a PIC.  One of the hangups is that at 200ft, the pressure on a 1/4"
button is 4.4lbs.  At sealevel, the switch would need at least 5lbs of force on
the button to remain useful at 200ft.

We are considering resistive ink technologies and looking for the pressure
differential of someone adding 1 lb of force.  Any other creative ideas would be
greatly appreciated.  Sorry if this is somewhat off topic.  This is a great assembly
of creative people (and I am using a PIC to read them.....)

--
Steve Nordhauser
Director of New Product Development
Imaging Systems
IEM Corp.
60 Fourth Ave.
Albany, NY 12202-1924
spam_OUTdigitalTakeThisOuTspamnycap.rr.com  http://www.iem.net
Phone: (518) 449-5504x21  Fax: (518) 449-5567

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2001\04\03@124756 by Alan B. Pearce

face picon face
use a hall effect device inside the pressure chamber which is sensitive enough
to detect a suitable magnet on a button. If the button/magnet assembly is
outside the pressure chamber then the activation force need not change between
surface and required depth.

Thinking about it while reviewing what I have written, it may also be possible
to do something similar optically - I do not know how thick the container needs
to be for 200 ft, but if it had suitable material then reflective opto sensors
where the led and optodiode are in a V looking for a reflective piece on the
underneath of the button may also work. The led could be pulsed on while sensing
the button. If more than one button is required this could also act as the
button select, with all the photo transistors wired in parallel onto a single
pin. :)

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2001\04\03@125256 by rottosen

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face
How about a momentary toggle switch instead of a push button switch?

-- Rich



Steve Nordhauser wrote:
{Quote hidden}

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2001\04\03@133301 by Chris Carr

flavicon
face
Steve Nordhauser wrote

> I am developing an underwater digital camcorder and need some suggestions
> on pushbutton switches for the body.  The requirements are that they are
fairly
> small (1/4" to 1/2"), sealed to 200ft, can handle harsh environments (sand
and
> sea water) and provide contact as long as depressed (unlike piezos which
put
> out a single pulse).  They should not draw much current when open and can
be
> read by a PIC.  One of the hangups is that at 200ft, the pressure on a
1/4"
> button is 4.4lbs.  At sealevel, the switch would need at least 5lbs of
force on
> the button to remain useful at 200ft.
>
> We are considering resistive ink technologies and looking for the pressure
> differential of someone adding 1 lb of force.  Any other creative ideas
would be
> greatly appreciated.  Sorry if this is somewhat off topic.  This is a
great assembly
> of creative people (and I am using a PIC to read them.....)
>
> --
Use a Reed Switch (or even a reed relay) on the inside of the pressure
casing with a bar magnet on the outside. When the bar magnet is in line with
the reed, the circuit will be closed. If the centre of the bar magnet and
the centre of the reed are aligned then when you pivot the bar magnet
through 90 degrees the magnetic field across the reed will drop to zero and
the reed contacts will open circuit. Simple, Cheap, no seals or pressure
differentials to worry about and it draws no power.

Regards
Chris

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2001\04\03@135552 by Raymond Choat

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face
try hall effect device such as AlegroMicro's A3144EUA. Magnet could be on
outside of case and hall effect switch inside. Only 3 leads on this package
(2 for power) (1 for signal on/off) output is digital compatible. This way
you need no holes in your case making it less likely to leak.
Wrong Way Ray

{Original Message removed}

2001\04\03@142756 by Barry Gershenfeld

picon face
Though it would involve the invention of a mechanical device, this
might give you an idea.

Make an optically operated device.  A plastic rod or some such that
interrupts a light beam.  The optics are inside the camera but the
button/slide part is outside.  The trick then is that you can let
water pressure on both sides of the button and don't have to
worry about the effects of pressure changes.

Barry


At 12:27 PM 4/3/01 -0400, you wrote:
{Quote hidden}

would be
>greatly appreciated.  Sorry if this is somewhat off topic.  This is a great
assembly
{Quote hidden}

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'[PICLIST] [EE}: Re: Need some switch ideas'
2001\04\03@150549 by Lawrence Glaister

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face
Hi Barry,
I made a small underwater flash unit and did not want to have the hassle of
finding a waterproof switch for the on/off switch. Since the enclosure was
plastic, I used a reed switch on the inside and a magnet on the outside
which when placed next to the reed switch turned the flash on. You could
expand this concept to a small keypad if needed. Ceramic magnets dont seem
to have a rusting problem.
=======================================================
Lawrence Glaister VE7IT             email: .....lgKILLspamspam.....jfm.bc.ca
1462 Madrona Drive                    http://jfm.bc.ca/
Nanoose Bay BC Canada      http://gspy.sourceforge.net/
V9P 9C9               http://members.home.net/cncstuff/
=======================================================
{Original Message removed}

'[PICLIST] Need some switch ideas'
2001\04\03@152643 by Gareth Bennett

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face
Why not Reed switches, which would be independent of altitude/pressure?
The operator just needs to wear a "magnetic ring" or the likes.
Just my 10c input!
Cheers

____________________________________________________________________________
________________________________________________________
         Gareth Bennett      EraseMEgarethbspam_OUTspamTakeThisOuTes.co.nz
         Systems LMR
         Otago/Southland Region
         New Zealand
{Original Message removed}

2001\04\03@181944 by Bob Ammerman

picon face
A variation on the optical theme....

Bounce a modulated LED at an angle from the interior thru the (Lexan?)
plastic enclosure to reflect at the plastic/water interface back thru the
wall of the enclosure to a phototransistor.

Placing your finger on the surface of the camera at the point where the beam
reflects might strongly affect the reflected signal.

Or, using the same technique by with a reflector on the back of a spring
mounted button. When the button is pressed in the reflector will bounce the
LED beam to the detector. When the button isn't pressed the beam won't be
reflected, or will miss the detector.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2001\04\04@024236 by Vasile Surducan

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face
On Tue, 3 Apr 2001, Alan B. Pearce wrote:

> use a hall effect device inside the pressure chamber which is sensitive enough
> to detect a suitable magnet on a button. If the button/magnet assembly is
> outside the pressure chamber then the activation force need not change between
> surface and required depth.

 Excellent idea with minor changes: use instead of hall, small reed
cheaper contacts. No magnet on the button. Sell with your device a pair of
gloves which have in two right hand fingers same material like electret
have.
( magnetic powder included in rubber )
Anyway the diver needs gloves...

I want 1 USD for any selled device... [hmmmmmm]

Vasile

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'[PICLIST] [OT] Re: Need some switch ideas'
2001\04\04@105648 by Steve Nordhauser

picon face
This is interesting.  I would have to be sure that there isn't any radiated light....
and I always need the LED lit.  We have talked about the reed/hall effect
ideas with magnets - they are very good for this application.  The problem
seems to be that they all still require a movable actuator.  As someone suggested,
if the back of the actuator isn't sealed, there is no pressure differential.  Unfortunately,
that means that sand could get under the button head and jam the switch.  So, they
solve most of the power issues, but not the pressure issue unless I am missing
something.
Steve

Subject:
       Re: Need some switch ideas
  Date:
       Tue, 3 Apr 2001 14:46:54 -0400
  From:
       Bob Ammerman <RAMMERMANspamspam_OUTPRODIGY.NET>

A variation on the optical theme....

Bounce a modulated LED at an angle from the interior thru the (Lexan?)
plastic enclosure to reflect at the plastic/water interface back thru the
wall of the enclosure to a phototransistor.

Placing your finger on the surface of the camera at the point where the beam
reflects might strongly affect the reflected signal.

Or, using the same technique by with a reflector on the back of a spring
mounted button. When the button is pressed in the reflector will bounce the
LED beam to the detector. When the button isn't pressed the beam won't be
reflected, or will miss the detector.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2001\04\04@120542 by Bob Ammerman

picon face
----- Original Message -----
From: Steve Nordhauser <@spam@digitalKILLspamspamNYCAP.RR.COM>
To: <KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU>
Sent: Wednesday, April 04, 2001 10:56 AM
Subject: [OT] Re: Need some switch ideas


> This is interesting.  I would have to be sure that there isn't any
radiated light....

There would have to be  something radiated, I'm afraid.

> and I always need the LED lit.

Naw, just pulse it when you want to check.

> We have talked about the reed/hall effect
> ideas with magnets - they are very good for this application.  The problem
> seems to be that they all still require a movable actuator.  As someone
suggested,
> if the back of the actuator isn't sealed, there is no pressure
differential.  Unfortunately,
> that means that sand could get under the button head and jam the switch.
So, they
> solve most of the power issues, but not the pressure issue unless I am
missing
> something.

How about having the actuator move horizontally along the outside surface
instead of in-and-out. Now no sand can get behind it.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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'[PIC]: Need some switch ideas'
2001\04\04@153010 by John

flavicon
face
Hello Steve & PIC.ers,

Have a look at  http://www.qprox.com
They offer capacitive proximity switch ICs, specially for
reading fingers through barriers.

or,

Go optical.  I diddled with an IR switch some time ago
for sensing finger presence through perspex.
It worked _quite_ well, but I lost interest before putting it
into any product.
I could make this up into a commercial unit for you if
you wanted (punt.. punt..) but I think you could just as well
do it yourselves.
See the genesis of this device at:-
PIC12cxxx Design Challenge - Apps. Handbook.
Microchip pub. DS40160A/3_017 pp 3-29
`Pulsed Optical Proximity Detector'
( Larry Nelson's design )



>Date:    Tue, 3 Apr 2001 12:27:48 -0400
>From:    Steve Nordhauser <RemoveMEdigitalTakeThisOuTspamNYCAP.RR.COM>
>Subject: Need some switch ideas
>
>I am developing an underwater digital camcorder and need some suggestions
>on pushbutton switches for the body.  The requirements are that they are
fairly
>small (1/4" to 1/2"), sealed to 200ft, can handle harsh environments (sand
and
>sea water) and provide contact as long as depressed (unlike piezos which
put

   best regards,   John

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Tel/fax:            Johannesburg  893 4154
Cellphone no:   082 741 6275
email:                spamBeGonejsandspamBeGonespampixie.co.za
Manufacturer & purveyor of laboratory force testing apparatus, and related
products and services.

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'[PICLIST] [OT] Re: Need some switch ideas'
2001\04\04@175343 by steve

flavicon
face
> As someone suggested, if the back of the actuator
> isn't sealed, there is no pressure differential.  Unfortunately, that
> means that sand could get under the button head and jam the switch.
> So, they solve most of the power issues, but not the pressure issue
> unless I am missing something. Steve

Here's another approach.
If you take the constant pressure inside the enclosure out of the
equation, the problem goes away. What you have at the moment is
a rod with 1 atmosphere on one end and a varying pressure (1-6
atm) on the other. If you can apply the external pressure to the
other end of the rod, the two will cancel each other out so the key
pressure will remain constant, regardless of depth.

My ascii art sucks so I'll try a description to illustrate.

Take one waterproof box and drill a largish hole that goes right
through both sides. Stick a rubber patch over both holes. Measure
between the inside faces of the rubber sheet an cut a piece of solid
rod to match. When assembled, pressing one rubber patch will
make the other deflect outwards. When submerged, the pressure
deflection on both ends is the same so the rod doesn't move and
the box is still sealed.
Now put a cross piece on the bar so that it looks like a letter "t"
and position the cross piece above the switch on the circuit board.
Make one of the outside rubber patches inaccessable to fingers
with a (unsealed) cover of some sort and you have a push button
that has the same actuation pressure at any depth.

Obviously as described there are some practical limitations. You
can apply the same basic concept using pivots, etc to make it fit
within your mechanical constraints. Assuming you are moulding
your own case, the extra plastic costs almost nothing and you get
the constant switch pressure you require.

PS. I've been looking for a business related reason to travel to
North America/Canada and try some ice diving. You obviously need
to hire a consultant on this one. :-)

Steve.



======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: TakeThisOuTstevebEraseMEspamspam_OUTtla.co.nz      fax +64 9 820-1929
======================================================

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2001\04\05@112749 by Steve Nordhauser

picon face
Steve,
I've got the image.  It would certainly work for equalizing the pressure.
I think it would even be feasible for the shutter button.  It would be
a problem for all the menu switches that would need to penetrate the
body (the internal boards would need to look like swiss cheese).

On the other hand, I would like to visit a consultant in New Zealand.....
Steve
--
Steve Nordhauser
Director of New Product Development
Imaging Systems
IEM Corp.
60 Fourth Ave.
Albany, NY 12202-1924
RemoveMEdigitalspamTakeThisOuTnycap.rr.com  http://www.iem.net
Phone: (518) 449-5504x21  Fax: (518) 449-5567

Subject:
       Re: [OT] Re: Need some switch ideas
  Date:
       Thu, 5 Apr 2001 09:50:50 +1200
  From:
       Steve Baldwin <steveEraseMEspam.....TLA.CO.NZ>



> As someone suggested, if the back of the actuator
> isn't sealed, there is no pressure differential.  Unfortunately, that
> means that sand could get under the button head and jam the switch.
> So, they solve most of the power issues, but not the pressure issue
> unless I am missing something. Steve

Here's another approach.
If you take the constant pressure inside the enclosure out of the
equation, the problem goes away. What you have at the moment is
a rod with 1 atmosphere on one end and a varying pressure (1-6
atm) on the other. If you can apply the external pressure to the
other end of the rod, the two will cancel each other out so the key
pressure will remain constant, regardless of depth.

My ascii art sucks so I'll try a description to illustrate.

Take one waterproof box and drill a largish hole that goes right
through both sides. Stick a rubber patch over both holes. Measure
between the inside faces of the rubber sheet an cut a piece of solid
rod to match. When assembled, pressing one rubber patch will
make the other deflect outwards. When submerged, the pressure
deflection on both ends is the same so the rod doesn't move and
the box is still sealed.
Now put a cross piece on the bar so that it looks like a letter "t"
and position the cross piece above the switch on the circuit board.
Make one of the outside rubber patches inaccessable to fingers
with a (unsealed) cover of some sort and you have a push button
that has the same actuation pressure at any depth.

Obviously as described there are some practical limitations. You
can apply the same basic concept using pivots, etc to make it fit
within your mechanical constraints. Assuming you are moulding
your own case, the extra plastic costs almost nothing and you get
the constant switch pressure you require.

PS. I've been looking for a business related reason to travel to
North America/Canada and try some ice diving. You obviously need
to hire a consultant on this one. :-)

Steve.



======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: EraseMEstevebspamtla.co.nz      fax +64 9 820-1929
======================================================

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2001\04\05@114150 by Alan B. Pearce

face picon face
>On the other hand, I would like to visit a consultant in New Zealand.....

There is some good diving in NZ, especially around the North of the North
Island, but then I guess you already knew that :)

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2001\04\05@172155 by steve

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face
Steve,

> I've got the image.  It would certainly work for equalizing the
> pressure. I think it would even be feasible for the shutter button.
> It would be a problem for all the menu switches that would need to
> penetrate the body (the internal boards would need to look like swiss
> cheese).

That was more for illustrating the concept. Picture a "V" shaped
piece of plastic behind a rubber keypad. The "V" pivots on the apex
and one end is below the button and the other is in the gap
between the buttons, the "V" only needs to be a few mm high.

> On the other hand, I would like to visit a consultant in New
> Zealand.....

I had two US customers "visit" last month. I guess you guys can't
be good at navigation. It always seems to take them a couple of
weeks and a lot of miles to find their way back to the airport.
And I have had business meetings at the Poor Knights Islands with
the dress standard being a wetsuit.

Steve.


======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: RemoveMEstevebTakeThisOuTspamspamtla.co.nz      fax +64 9 820-1929
======================================================

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2001\04\05@181312 by rottosen

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Here in Denver, at the foot of the Rocky Mountains, the standard visit
is timed to end early on Friday. This leaves time to get to the ski
slopes for weekend skiing.


-- Rich


Steve Baldwin wrote:
{Quote hidden}

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'[PICLIST] Need some switch ideas'
2001\04\06@052702 by P.J. McCauley

picon face
A good way to do this might be to use a magnetic reed switch inside the
housing activated by a small moving magnet on the outside of the housing.
The mechanism for moving the magnet  may be exposed to the same pressure as
the outside enviroment. You can either let this mechanism be exposed to the
water or if you need it sealed, fill it with a liquid which has the same
compressability as water. The resulting switch may be a little bulky, but is
absolutely flood proof. At 200 ft any hole which has to be made in the
housing is another potential way to flood the camera.
If the switch needs to be made smaller then you can get away with a smaller
magnet and shorter actuation stroke by using an electronic sensor like Hall
effect or magneto resistance. Of course you need some extra electronics in
the housing to drive/read these sensors, but the size savings on the
actuator itself might be worth it.
It is also possible to do much the same thing using an opto reflector sensor
inside and a reflector on the end of the external actuator.
In either case a spring loaded rotary or sliding actuator may save some
space rather than a pushbutton.

Please let me/ the list know how you get on with this project if you can.
I've thought about this a bit with regard to housing my own camera and have
some other (untested) ideas. I really must get around to doing something
about it before I'm too old to dive.................

Joe

{Original Message removed}

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