I'm working on a modification project for a pet tracker. The current container is a sealed plastic square with a few very small openings (smaller than a poppy seed) for a speaker. For a dog, it would be no problem, but for a cat (or a kitten), the container is just a little too large to be convenient for the animal.
Before I cut into it (the device, not the cat), I have a question I can't answer with enough confidence to start the project.
I have the new case, half a contact lens case. It's watertight with a screw top so I can get back in to change the battery. The current layout has the components laid out like a ranch house. I want to rebuild like a two-story job by stacking so that they'll fit a more efficient volume. (Right now it's about 1.5" x 1.5".)
Is there an adhesive that will allow me to anchor each component securely to the plastic interior? Ideally, I'd like to find something like Elmer's glue. Pour in, stick a component in place. Add more. Place next component, ending up with something like a puck that fills up the entire interior volume, with the speaker portion anchored carefully up against the opening in the case and the battery tabs at the very top so that I can put in a new battery without trouble.
Sorry for the detail, but I thought that if I didn't explain it sufficiently, the advice might not be useful.
I would use epoxy. It has the advantage that it doesn't depend on any solvents evaporating. You just mix two components and they cure, even if you have very thick layers. There are different kinds of epoxy that cure after different times (5 minutes, 60 minutes, etc.). Ebay is usually a good place to find epoxy but you can also get it from any R/C hobby shop.
If there are components that emit lots of heat, it might be better to use Fujik or if you're a millionaire you can use arctic silver thermal epoxy.
I'm pretty sure the components can be fit in to the contact lens case. If not, I can buy a screw-top capsule online. The current case is a square, with at least 1/4 of the footprint taken up solely by the battery (about the same diameter as a dime). In a worst-case scenario, I break it and I'm out $25. Even if I can just shift the battery portion over the components, it'll fit fine on a collar. But I'd like to avoid doing any soldering if possible; I know my limits, and needle-threading soldering is something I face with trepidation.
You might try hot glue. It is fairly strong, and is somewhat removable depending on how it is applied. Put small drops on toothpick for small application.
Right now, the whole thing is still in one connected piece. I managed to extract it from the original case without breaking it. There's three items: the circuit board, the speaker and the battery.
The battery's about the size of a dime. I wasn't sure if there would be enough wire on the original assemblage of bits to relocate the battery to above the circuit board. If I HAVE to, I will replace the current tab holders for the large battery with a smaller housing, which would require a tiny amount of soldering. But, like I said, it looks like a very finicky bit of soldering (to me).
What I hope to finally have is a circuit board/speaker arrangement that has been encased in something (leaving the mouth of the speaker clear) with the wires leading to the battery clip emerging from the block of encapsulant. And that whole thing ends up in a modified contact lens case.
Again, sorry for all the detail. I'm not trying to bore everyone to death. It's just that I see it clearly in my mind, but I don't want to pour in the Fujik (or whatever else is recommended) and have people howling, "Oh God, what were you thinking? Everyone knows you can't encapsulate a circuit board in a polymer. Are you mad?"
I have a caution about encapsulation though. This is an RF transmitter/receiver, right? Sometimes encapsulation will alter the RF components and the frequency will be off.
It should be something flexible, due to the issue of things changing size at different rates for a given change in temperature.
If you decide to use silicone, select carefully. Some kinds cause rapid oxidization of metal. If it smells like vinegar, don't use it on anything metal. Those are usually the caulks that advertise water cleanup of uncured silicone.
A tube from an auto parts store is virtually guaranteed to be safe on metal.
However, I put in my vote for hot glue. You are merely trying to keep the components fastened down, not seal it, and it is a sealed container, anyway. A thin plastic diaphgram could serve to let sound from the speaker out.
Hot melt glue has the advantage it can be removed/reworked somewhat with hot-air gun
should you ever need to do this - messy though.
However it does melt/soften in hot places (and cats are pretty heat tolerant), so I'd ensure
its also capped in the device should the cat befriend a hot radiator!
I discovered it melts in parked car in English summer conditions (airtemp 25C at most!).
Different brands may behave differently of course...
If you don't heat the entire thing, but merely stick things in place, hot glue can often be peeled off.
The craft sticks may soften under conditions that, as MarkT points out, your cat may tolerate. However, the regular hot melt or the yellow sticks often sold as carpenter's hot melt or high temp or tough hot melt would not melt in those conditions.
zoomkat:
Well, if you don't mind having a cotton swab or toothpick also glued to the project.
And maybe on fire
Cyanocrylate applied to cotton swabs or pieces of cotton usually heats up the point where it starts smoking and bursts into a flame :o
Also, hotglue can be removed easily with alcohol, just a few drops on the glued line, and it lets go. Same goes with Cyanocrylate, you just use Acetone in that case.
It's a silicone rubber that can be molded into any shape and cures in 24hrs. I've used it a couple of times and found it to be very good at potting electronics.
Cyanocrylate applied to cotton swabs or pieces of cotton usually heats up the point where it starts smoking and bursts into a flame :o
Also, hotglue can be removed easily with alcohol, just a few drops on the glued line, and it lets go. Same goes with Cyanocrylate, you just use Acetone in that case.
// Per.
Unfortunately acetone is a good solvent for certain plastics too. You'd be OK with
polythene or PTFE, but polycarbonate and acrylic will disolve IIRC.
