I've got my Max7221 matrix sketched out and working in principal but now I want to scale it up (covering an area of some square feet). At some stage in the future I'm probably going to want to re-use the LED's and change the layout and it stated me thinking about robustness and reusability.
Jumper wire and breadboards are fine, but for outside use, or where there might be numerous insertions over time it's hardly ideal. In my mind I'd thought that a small vero board square with LED mounted, plus a small ribbon cable assembly for the signals but I'm a) not sure that's not over engineering the solution or b) just a dumb/expensive idea.
How do people make the jump from breadboard to semi-permanent? And on a related note, any thoughts on waterproofing (rain rather than submersion)
I like the idea of sharing ideas on enclosures and cabling, in order to get to a complete thingie. I have made a compass, cooling water temperature, RPM monitor for my boat, and bought a sealed box, some sturdy plugs and added gun glue to seal all the openings.
How do people make the jump from breadboard to semi-permanent?
I don't use breadboard as I find it can cause more trouble than it is worth. I solder stuff onto veroboard. This is more permanent than semi permanent but you could add headers like on the aruino board to make it more reusable.
If I want to try something I just solder the components together like you would see them on a schematic, using the leads and tinned copper wire. This works better when using discrete components rather than ICs.
I mostly don't do breadboarding, unless there are some component values I think I'll need to tinker with to get the circuit right.
I go straight to solder, using a prototyping board like this or this. Futurlec has some nice ones, too, but you need to plan ahead because they often take a month or so to deliver.
One important lesson that's better to learn from someone else's experience: if you do breadboard first, keep the breadboarded version assembled until you've confirmed that the soldered version is working. Sooner or later, you will make a mistake doing the transition, and having the original for comparison will save a part of your anatomy that you'd rather not lose.
For weatherproofing, you can get mil-spec connectors on the surplus market, but even then they're pretty expensive. One thing that can help is to minimize the number of wires you run out in the elements: put an Arduino (or some other CPU) in the box, and send commands to it via serial, instead of running lots of signals to the box via ribbon cable. Then you can do the interconnects with something like DIN connectors, and use electrical tape to get a "usually-good-enough" seal. Instead of putting a bulkhead connector on the box, bring out a "pigtail" with a DIN on the end so you can tape the two connectors together.
Straight to solder... I can barely tell my butt (the a word gets translated to Tushy of all things!) from my elbow so breadboarding is an essential stage right now.
But even then, say I've an 8x8 grid. If at some stage I want to increase the distance between nodes, or re-config it to 16x2 or some such, what I'm looking for is idea on how to futureproof those kind of changes.
I don't enjoy soldering enough that I wish to spend hours each time redoing hundreds of joints so I'm searching for pin/plug/socket/cable combos that will make this a bit earier down the line.
So even if I went straight to solder, the question still remains. If I'm looking for a semi-permanent cable connection with headers, cables etc, but that is more resillient to movement/fiddling/squirrels than jumper wire straight into a .100 socket, what works well at a reasonable price?
Doing a bit more thinking, I wondered about Cat5 cable and RJ45 sockets. The downside is that the sockets are > GBP 1 each, so sixty quid for connectors before you get started is a little steep.
But, Cat5 with pins crimped on the end would do nicely (I think)? Any thoughts? Could do strain relief easily enough with a cable tie.
IMO, the individual wires in a CAT5 cable are too thin and would give you grief over time. I would use a D-sub connector. They are relatively cheap, easy to quickly solder/desolder wires if you need to change something, easy to put together and pull apart, can be mounted to a case, and readily available in 9, 15, and 25 pin w/ strain relief.
If you really need waterproof, and the device is largely static once installed, consider using liquid-tight conduit and boxes. At each device, use PC-mount screw terminals, and fish whatever number of whatever gauge wires you need to and from each location. If you don't truly need it to be waterproof, you can substitute EMT or ENT for the liquid-tight for lower cost. As far as rugged interconnects, consider XLR. They're widely used in entertainment with good reason, and are available in up to 7 pins per connector (although the higher pin counts are less common and therefore more expensive). But they're quick to make/break, have a positive lock, and e.g. Neutrik make very nice tool-less assembly models. You can also get RJ-45 (and some other) connectors with an XLR-type shell that provides XLR robustness to those interconnects.
Also, I'll ++ to the idea of distributing your processing throughout the system. 4-6 conductors for power+serial is a much more robust proposition than 80 conductors feeding directly to your LEDs for reasons of cost, voltage drop, fragility, cable size weight and cost, interconnect size and cost, labor to install all of the conductors, etc etc.
