I’m contemplating building a line of reusable “Lego brick”-like circuits such as analogue signal attenuators and amplifiers, to be used during prototyping. The biggest concern with this is that, as they’ll likely get a lot of rough handling, they’ll need a robust protective case. See here for more context.
I’m investigating the use of small ABS cases, which seem to be economical in the size I’m looking at. For £6 I’ve ordered a set of five two-part snap fit cases measuring 60mm x 37mm x 17mm (roughly 2⅓in x 1½in x ⅔in for those still using old money.) But I’d also like to look at another possibility: potting, which is a broad name for any process that encases an entire circuit in a protective layer. Typically this is done to protect the circuit from a hostile environment such as an aquarium.
I’ve looked at a number of different methods, but I’m still a little confused. Does anybody have any experience with potting? I’m particularly interested in making my small circuits robust enough to withstand being handled a lot, but I’m also receptive to any insights on this topic.
I think that Mehdi did that in one of his ElectroBOOM videos but it wasn’t the one I thought (channel link only) but if I recall correctly he simply put a bed of hot glue in the base of a cardboard box, let it dry, then put the circuit on that and drenched it in more hot glue that he melted in a pot. I don’t know that I’d recommend this if you’re generating something that puts off a lot of heat, but then if that’s what you’re doing you probably shouldn’t pot the circuit in anything, else it will probably burn itself up pretty quickly, won’t it?
I “potted” some wireless circuitry for a submersible robot about 10 years ago. Started with the same wax I used for guitar pickups and had a frame I could wrap with tape and sheet plastic afterwards. It works well structurally but the interface is always tricky.
Resin is a nightmare with guitar electronics as just one bubble can give you freaky results.
I like the Lego idea. I use pill boxes for some swap out functions on fx. I like that they click together. All dead bug freeform inside with smd glued around the ic and thin glazed hookup wire.
Personally I’d go for a flat wide board at the back of your case with all your small circuits and headers so any module can patch them in.
I’ll keep an eye out for Lego like boxes… there are a lot of things like this in robotics. (Another hobby)
Thanks everybody. I had a Phillips electronics kit as a child, and remember how cruel those spring connections could be to small fingers. The transistors and other delicate components were mounted on small circuit boards, though, and in part that’s what inspired my idea here.
I love the idea of using pill boxes. I have a seven day pill sorter I got from a pound shop a few years ago, and I’m always surprised at the number and variety of different containers they sell in those places.
Heat dissipation steers me in the direction of plastic boxes, but I haven’t given up on the idea of potting in resin or something. I would have to install heat sinks and even then the lack of air flow would make them far less efficient than they would normally be. I guess the secret would be to not pot anything I wasn’t confident could endure for a few months.
Finally, the notion of having a backboard with semi-permanent wiring has some merit for prototyping. With the board providing rigidity I wouldn’t have to worry about rough handling. One of my current ideas is to use velcro on the back panels to hold my “bricks”, but that implies reserving blank space on the panels. A separate board would be just fine. A couple of A4 greyboard lain sideways, perhaps. 2mm or even 1mm thickness would do because we’re not plugging and unplugging patches all the time. This would have implications for signal path length so I’ll have to see how it works out.
epoxy isn’t to hard to use . just like any mold making , make box to contain material , place your electronics , pour the epoxy , wait awhile than you have an indestructible block with wires hanging out .that is a bit over simplified and there is draw backs like no repairs .
You can encapsulate with epoxy putty (milliput).
Just fold polythene from a plastic bag over the circuit then shape the putty on either side. When dry the blocks can separate and reconnect with a tie, band or Velcro. Hard as nails.
These reusable circuits sound like a sub-modular to me. So, in stead of making whole modules, like an ADSR, you want to have 4 timer circuits that can be triggered and manipulate some amplitude to e.g. build an ADSR? Sounds like functional decomposition (used in software engineering) gone hardware.
It would be an interesting exercise to break down modules into functional blocks to understand core functions. Different modules constructed with different blocks. Sounds like something Pure Data should be able to model.
You will not be shocked to be reminded that I’m a software engineer of some four decades standing.
I don’t envisage exactly the kind of decomposition you describe, though. My needs are limited to gluing together digital and analogue components so that they work together seamlessly at the patch cord level. As I remark on the fast prototyping thread, the function of these “Lego brick” circuits is broadly limited to signal conditioning.
In modern software engineering parlance, the analogue modular is a façade erected to ease interfacing with the wetware. Sometimes the modules themselves are implemented in software. It’s not exactly a new idea, but my decompositional approach doesn’t seem to have been tried at this level, reusable circuitry included.
Hot glue is removable with either heat, right, or with cold spray. Epoxy not so much. Oh, there is also that hot water meltable plastic craft stuff. I use it to repair furniture and make handles for tools. It is super tough. And it is reworkable and nontoxic. I think you can heat it in a double boiler so it does not get wet.
I’m talking about very small assemblies costing pennies. A tl07x and a few resistors. The likelihood of needing to remove the protective medium is very low, and there would be little to be gained from a successful attempt.
