Author Topic: Very small and thin transparent enclosure  (Read 4927 times)

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Offline jmajaTopic starter

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Very small and thin transparent enclosure
« on: February 05, 2019, 06:21:35 pm »
Where can I find an enclosure for a prototype/small number product with the following specifications?
-Needs to be transparent or at least have windows for several LEDs and sensors (IR and visible).
-Needs to be very thin. The PCB+components will be 4 mm. Thickness is critical, thus hoping to find 6 mm etc. outside height.
-Size could be 30x40, 40x50, 30x80, 20x80 mm or something similar.

It would also help, if the case is water tight and can be opened for battery replacement.
 

Offline ebastler

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Re: Very small and thin transparent enclosure
« Reply #1 on: February 05, 2019, 06:33:58 pm »
Something like this, maybe?
https://ace-cases.com/product/compactflash-cf-case-for-single-cf-cardsmart-memory-media/

Similar cases for SD-Cards are also available, but may be too small.
None of them are water-tight, I'm afraid.
 

Online Ian.M

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Re: Very small and thin transparent enclosure
« Reply #2 on: February 05, 2019, 06:49:38 pm »
Short of milling a case out of aluminum bar stock with a raised rim to protect the edges of a clear acrylic or polycarbonate sheet lid, with an O ring groove for a seal and a line of tapped holes outside the O ring groove to screw down the lid, I think that's going to be very difficult in small quantities.    Even so, 6mm thick is unrealistic - you might manage 7mm - as IMHO 1mm is too thin for a plastic lid that needs to be both removable and make a watertight seal, especially if its got to have countersunk screws through it.   
 

Online Nusa

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Re: Very small and thin transparent enclosure
« Reply #3 on: February 05, 2019, 07:12:34 pm »
Clear shrink-wrap tubing. Cut long and seal ends with glue if you want water protection.

For battery replacement, cut it off and use a new piece of tube.
 

Offline jmajaTopic starter

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Re: Very small and thin transparent enclosure
« Reply #4 on: February 05, 2019, 07:43:00 pm »
One thing I forgot to mention was that there must be a way to fix this enclosure to a surface. E.g. a two holes for webbing etc.

Could heat shrink tube really work for this? I could put the fixing wholes to the PCB. Or use the extra heat shrink tube for fixing. Would it seal well enough against the PCB or itself. I haven't used that big heat shrink tubes before.

Would the glue still be transparent?

Battery replacement is not a must and could be done with a heat shrink. The battery should last several years, which may be as long as the useful life anyway.

The product will not be submerged, but will be outdoors in a rain.

One idea I just got from polycarbonate. Maybe it could be feasible to to use 1 mm and 4 mm polycarboate? Cut a rim out of 4 mm and the glue or fuse the 1 mm top and bottom to it. https://www.cutplasticsheeting.co.uk/blog/uncategorized/how-to-glue-polycarbonate/

Can't be opened and closed, but would be rather strong and easy to mill.
 

Offline ebastler

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Re: Very small and thin transparent enclosure
« Reply #5 on: February 05, 2019, 08:04:59 pm »
I think it's time for you to tell us about your actual use case. It's a bit frustrating to make a proposal and then just hear back "Ah, and it needs to do this too"...

If it attaches to a table larger object, why does it have to be so thin? And attaching with webbing??  :-//
« Last Edit: February 05, 2019, 08:14:58 pm by ebastler »
 

Offline jmajaTopic starter

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Re: Very small and thin transparent enclosure
« Reply #6 on: February 05, 2019, 08:13:53 pm »
It will be attached to a canvas outdoors. It can't stick out much from the canvas.
 

Offline ebastler

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Re: Very small and thin transparent enclosure
« Reply #7 on: February 05, 2019, 08:16:33 pm »
It will be attached to a canvas outdoors. It can't stick out much from the canvas.

So the actual use is a trade secret, since it will make you rich.  ::)
Fine, but I am no longer interested in guessing games. Maybe others are.
 

Offline jmajaTopic starter

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Re: Very small and thin transparent enclosure
« Reply #8 on: February 05, 2019, 08:29:07 pm »
So the actual use is a trade secret, since it will make you rich.  ::)

Certainly will not make me rich. If I thought it would, I would order a custom enclosure from some manufacturer. Since I don't see making many of these, I don't want to spend a lot of money on the enclosure.

But sorry I don't feel comfortable revealing the application.
 

Online Nusa

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Re: Very small and thin transparent enclosure
« Reply #9 on: February 05, 2019, 08:53:14 pm »
You'll have to do some experimenting to determine what's suitable, especially if you need abrasion resistance as well, which being attached to canvas implies. Direct sunlight will degrade most unpainted plastics in a couple years...I know generic tie-wraps used outdoors don't last much longer than that.

My only other thought is embedding your device in epoxy resin. The learning curve on that will be higher, unless you find someone who already knows how it's done. Here's a page that might get you started: https://hackaday.io/project/21914-resin-in-resin
 

Offline coppercone2

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Re: Very small and thin transparent enclosure
« Reply #10 on: February 05, 2019, 11:40:51 pm »
I think it's time for you to tell us about your actual use case. It's a bit frustrating to make a proposal and then just hear back "Ah, and it needs to do this too"...

If it attaches to a table larger object, why does it have to be so thin? And attaching with webbing??  :-//
sometime sthis forum makes you feel like a unpaid kinda voluntary product designer huh :-DD
 
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Online SiliconWizard

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Re: Very small and thin transparent enclosure
« Reply #11 on: February 05, 2019, 11:58:39 pm »
Thin, transparent, water-tight, can be opened (I guess "easily")... yeah. Almost Santa's list. ;D

Maybe recycle old (or not) watch housings? You can find them water tight, with a nice transparent window, and they can be opened. A typical watch may not be large enough I guess..., but that's worth a look?
 

Offline AlcidePiR2

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Re: Very small and thin transparent enclosure
« Reply #12 on: February 06, 2019, 02:20:26 am »
You could do it easily with a 3D printer.

1mm thickness is fine. Using flexible material, you probably can have a water tight lid. No problem to add some pads with hole to screw it to something.
 

Online Ian.M

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Re: Very small and thin transparent enclosure
« Reply #13 on: February 06, 2019, 02:49:53 am »
3D print something or laser cut polycarbonate and glue it up like a layer cake, and you'll be replacing the enclosures annually due to UV degradation.   Painting them opaque black and you'll cure that but then the optical and IR sensors wont work.

Since its a prototype, why not solder them up out of  brass shim stock, with epoxied in mica windows for the sensors? Tin the whole exterior for better corrosion resistance.  You wont be able to make the battery easily replaceable without desoldering the cover.


It will be attached to a canvas outdoors. It can't stick out much from the canvas.
But sorry I don't feel comfortable revealing the application.
So, you want to cam bug the toilet tent at a festival?  :popcorn:  >:D
« Last Edit: February 06, 2019, 02:55:17 am by Ian.M »
 

Offline daniel444

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Re: Very small and thin transparent enclosure
« Reply #14 on: February 06, 2019, 03:54:13 am »
just buy an off the shelf  aluminum box and cut your own perspex  lid for it
 

Online Kasper

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Re: Very small and thin transparent enclosure
« Reply #15 on: February 06, 2019, 06:55:46 am »
Be careful what material you put infront of the IR sensor. Transparent to visible light does not mean transparent to IR. You also want immunity to sunlight if it's outside.

I'm guessing by IR sensor, you mean PIR motion sensor?  If thats true, safest bet is get a PIR with window (fresnel lens) with zones and detection distance that meets your specs. And don't put any other material infront of it.
 

Offline jmajaTopic starter

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Re: Very small and thin transparent enclosure
« Reply #16 on: February 06, 2019, 07:52:19 am »
The IR is a a set of proximity sensors using a set of IR LED's. They work at 850 nm so very close to visible light. Seems to work OK through some clear plastics I have tested, but naturally the actual material to be used has to be tested as well.

The goal is to measure visible light lx as well and the proximity sensor has a sunlight canceling system, which seems to allow measuring in direct sunlight.

Then there are visible LED's to inform the user + BLE to send data to a mobile phone.

Sensors and LED's are on both sides of the PCB thus the enclosure needs to be transparent or have windows on both sides.
 

Offline mikeselectricstuff

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Re: Very small and thin transparent enclosure
« Reply #17 on: February 06, 2019, 07:59:35 am »
For prototype qtys :
a)  two lids from Hammond clear plastic boxes, back-to-back.
b) a sandwich of 2 sheets of acrylic, with a spacer frame +PCB in the middle

For production, the tooling cost for an injection mould for a simple shape like this wouldn't be very expensive
 
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Offline jmajaTopic starter

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Re: Very small and thin transparent enclosure
« Reply #18 on: February 10, 2019, 09:52:32 am »
I ordered some clear heat shrink tubing and did some testing. https://www.digikey.fi/product-detail/en/3m/FP301-1-48--CLEAR-24-PCS/3M161366-ND/3864906 This one has no adhesive.

The IR proximity sensor seems to work just fine through it. It increases the base level, but SNR is about the same.

The PCB+battery is now about 24x61x4 mm. If I use the heat shrink tube, how could I seal the ends?

I'm starting to like the idea of "plastic wrapping". What other ways are there to achieve this? Vacuum bagging? Laminating?
 

Online Kasper

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Re: Very small and thin transparent enclosure
« Reply #19 on: February 10, 2019, 05:08:16 pm »
I like using hot glue to seal the ends of heat shrink tubing but thats usually with much smaller tubing and I've never tested its waterproofing quality.

You could try hot glue then pinch with needle nose pliers to crimp it shut.
 

Online Nusa

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Re: Very small and thin transparent enclosure
« Reply #20 on: February 10, 2019, 07:51:06 pm »
I've used hot glue with personal one-off projects. Should be fine for a prototype...you'll  have to evaluate it for production. Can be smoothed when hot and trimmed with a knife when cold.

For cold glues, I suspect super glue would work. Never tried myself.

My other idea would be using the right size end plug for the tube to shrink around. In your case, perhaps a 4-5 mm thick sheet of plastic or wood cut to the width of the pcb. Butt pieces up to the pcb ends, shrink the tube, then cut both ends off to get nice edges. If you make the plugged ends long enough, you can drill them for mounting holes.
 

Offline reboots

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Re: Very small and thin transparent enclosure
« Reply #21 on: February 10, 2019, 08:46:29 pm »
This is a little more than 6mm thick, but it might fit your other requirements:

http://www.witzsportcases.com/id-badge-holders/see-it-safe-new.html

Waterproof PVC badge holders are a common product. This listing ships from USA, but something similar may be available within your locale:

https://www.ebay.com/itm/183568594557

You will definitely want to test the waterproof claim. As other commenters have mentioned, clear plastics (especially PVC) won't last forever outside.
« Last Edit: February 10, 2019, 08:48:11 pm by reboots »
 

Offline jmajaTopic starter

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Re: Very small and thin transparent enclosure
« Reply #22 on: April 12, 2019, 06:51:05 am »
Clear polyolefin heatsink from 3M worked OK and it was possible to seal the ends by melting. I could not find one with glue.

However, I'm trying to go forward with a custom enclosure made from polycarbonate. I have designed it to be openable and sealed with an O-ring. The O-ring is set up as piston cylinder style.

The PCB became even thinner (3.1 mm) allowing the enclosure to be only 4.7 mm. Now my problem is to find suitable screws for such a small and thin enclosure. The screws need to be recessed into the enclosure. The total lenght of the screw (including the head) must be less than 4.5 mm, preferably 4 mm to allow some tolerance. The thickness of the enclosure halfs at the screws is 2.2 mm, since there will be 0.3 mm thick fabric in between. Due to O-ring configuration no compression from screws is needed, it's enough to just keep the halfs together.

The first installation and possible battery change after a few years is done by the user. The screws must work at least 3 times.

What kind of screws would fit this application? Thread forming screws or machine screws? What kind of nut arrangement for the latter?

The suitable size would be M2 (or #2). Thread forming at only 4 mm length are very hard to find and surpricingly expencive. Will they hold with such a short thread? Only 1.5-2 mm.

Also M2 thread incerts for only 2.2 mm thickness are hard to find. I found one, but it seems not designed for recessed installation. Square or hexagonal nuts can be found at 1.2 mm thickness. Would making a recession for it work?

The screws need to tolarate weather. Maybe A2 or brass is OK?

At least the first enclosures will be CNC machined, since the mold cost approximations I have got have been 5 000-10 000 €. Is that expected?
 

Offline jmajaTopic starter

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Re: Very small and thin transparent enclosure
« Reply #23 on: April 12, 2019, 08:01:19 am »
Would even tapping M2 threads to this 2.2 mm thick half work? Obviously not anymore, if the enclosure will be molded.
 

Offline Skashkash

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Re: Very small and thin transparent enclosure
« Reply #24 on: April 12, 2019, 09:05:01 am »
Since we are throwing ideas out there.

Impulse seal it in pouch?

Like these marker lights (as an example)
https://countycomm.com/collections/all/products/maratac-mas-micro-adhesive-strobe-3-pack-u-s-a-nsn?variant=20534147317830

May want a top stiffener piece of pcb or plastic on top of circuitry. Extend ends and punch mounting holes like a luggage tag.
« Last Edit: April 12, 2019, 09:06:48 am by Skashkash »
 


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